Dominique Osso

Marie-Hélène Laurent

The correct price or the fair price? A quali-quantitative analysis of the formation of price for energy retrofit works in the residential sector in France

This paper tackles the crucial issue of price structure in the energy retrofit market of the private residential sector. It is based on a quantitative study of retrofit prices in France (1,000+ invoices) and a qualitative sociological survey of installers (25 open-ended interviews). We show a strong dispersion of prices within single retrofit-work categories (e.g. boiler, insulation). Half of the dispersion is explained by technical and economic reasons (brand and quality of product, housing size, type of company, discount…). This means that from a technical standpoint, the price is correct. Other components of the price are revealed by the qualitative survey.

On the customer side, the refurbishment market is marked by a strong uncertainty. It is technically complex and there is a concern about poor workmanship, hence the role of reputation and trust. These are factored in the price as a "confidence premium" which makes the price fair from the customers' point of view.

On the installer side, the price is formed at the crossroads of three characteristics: the perception of the household willingness to pay, the management practices of the company (profit margin calculation, load plan) and an adjustment to current local market prices. The fair price from the installer point of view is the price that allows his company to survive or make profit and to win new contracts. However, a determining factor of the price lies in the installer's recommendation of exactly which work to do and with which material or equipment. For a given energy performance, several technical solutions exist that impact the final price.

To conclude, we note that observed prices may differ from the technically "correct" price but this doesn't mean that prices are inaccurate. Prices incorporate qualitative dimensions such as the accessibility of the site or the work quality of the company (being on-schedule, cleanliness of the work, etc.) that make them "fair" in practice. As a policy consequence, rather than a direct intervention on prices which is complex, governmental action might focus on standardizing the presentation of quotation, craftsmen company management and on assisting customers in their choices.

Introduction

France has made a commitment to cut its greenhouse gas emissions by 75% by 2050. In France, buildings are one of the levers identified in government policies to reach this objective, since they are the 2018 International Energy Policy & Programme Evaluation Conference -Vienna, Austria major energy-consuming sector in France and one of the largest emitters of greenhouse gases (ADEME 2013). Renovating existing buildings is a priority for reducing fuel consumption to an acceptable level; but the diffuse nature of the residential sector complicates identifying what mechanisms to implement to promote successful, large-scale renovation.

This fact is well known to the public authorities which have, in recent years, set ambitious targets and implemented measures to refurbish housing. One objective laid out in the Law on Energy Transition for green Growth (2015) is to of renovate 500,000 homes per year from 2017, of which 380,000 are private housing units. In order to achieve these objectives, public authorities have chosen to encourage households to carry out retrofits through subsidies (tax credits, energy efficiency obligation, etc.). More recently, more restrictive standards on energy performance have been passed in the thermal regulation in existing buildings (2017), particularly thresholds for components used in renovation such as windows or insulation materials.

This has been accompanied by inflationary price trends (INSEE 2017) in a sector in which prices and margins are already nebulous and controversial (Baulinet et al. 2014, Chesnay and[START_REF] Chesnais | Rénovation énergétique : les professionnels n'assurent pas[END_REF]. The question of fair pricing for refurbishments is crucial to secure the market's dynamics and consequently to increase the number of successful renovations undertaken. Whereas the profession considers that "there is no standard price... because prices depend not only on the performance and the quality of the products or equipment that are used but also on the actual situation of the dwelling and people's lifestyles" (Batirama 2016a), consumer associations point to a "stagnation of the market [due] to a lack of consumer confidence" (Batirama 2016b).

The price appears as a central but under-researched issue in the energy efficiency retrofit debate of the private residential sector. As mentioned above, the level and breakdown of prices, margins and the distribution of value within the sector are not only notoriously poorly understood but also subject to controversy. It is this lack of knowledge that this article intends to remedy, thus helping to inform the debate. More precisely, this article tackles the issue of price dispersion in energy efficiency retrofits. Indeed, one of the major characteristics of this market is the wide price dispersion, for a given type of work. The aim of this article is not to study the level of renovation prices but to analyse the reasons for their wide dispersion, a phenomenon that is even more nebulous than price levels themselves and more interesting in terms of potential recommendations for widespread expansion of the market.

In fact, from the point of view of economics, the price of renovation work has very distinctive characteristics. Energy efficiency retrofits can be considered as a "belief and trust purchase" whose quality is unknown at the time of purchase and may become apparent only through usage [START_REF] Giraudet | Qualité des travaux de rénovation, asymétries d'information et garanties de performance énergétique[END_REF], which has consequences for the price (in particular, on the willingness of households to pay). Also, to analyse the prices of the renovation, it is advisable to appeal not only to economics as a science but also to economic sociology. The latter considers that markets are not interfaces between supply and demand in which the outcome of the balance of power is the economically rational constitution of a price. If prices are indeed at the heart of markets, they are shaped by social dynamics that go beyond the simple economic balance between supply and demand [START_REF] Beunza | A Price is a Social Thing: Towards a Material Sociology of Arbitrage[END_REF][START_REF] Callon | L'emprise des marchés[END_REF]. From this point of view, therefore, price analysis involves analysing the context of the market in which they are shaped, taking into account dynamics and factors other than those conventionally considered by economic analysis.

That is why this article intends to remedy the lack of knowledge on the dispersion of renovation prices by implementing a dual approach: technical-economic and sociological. The quantified investigation of the price structuring of the renovation market is complemented by a qualitative field survey on the actual practices of the actors in order to be able to understand and interpret the quantified results in a sensible way. The objective of this study is not to give THE PRICE of energy efficiency refurbishment work, which, we will see later, is illusory, but to understand how the prices vary and the reasons for these variations. Our choice of a mixed approach (quantitative and qualitative) to a problem that is notoriously little addressed and controversial is original to this paper.

The first part of the paper is a techno-economic quantitative analysis of the prices of energy retrofit works in the diffuse (owner-occupied) residential sector in France. It focuses on the breakdown and heterogeneities of prices in that market. The second part of the paper proposes a qualitative sociological analysis centered on the role of the intermediaries (installers) in the sector and on the socioeconomic mechanisms of pricing to supplement and clarify the quantitative analysis. Finally, we conclude on the potential implications on energy policies that our results suggest.

Quantitative analysis

Methodology

This section presents the data and methodologies used to analyse the observed price structure of energy efficiency retrofit in the scattered residential sector. Two complementary approaches, both based on invoice analysis, have been implemented to estimate the variations in the price of work because they offer different information. A first approach analyses the invoices for the work carried out in detail1 , the so-called "technical" approach on a hundred of renovation work. The second approach uses a less detailed 2 approach but more consistent in terms of volume, the so-called "main sample" approach on several thousand of invoices. The items of work studied concerned both the insulation of the building shell (roofs, walls, windows) and heating systems (condensing boiler, air/water and air/air heat pump (HP)) for one and the same year. Prices are analysed separately for each type of works, even when several works are jointly done. However no distinction from the two samples ("technical" and "main") are presented because the results are similar or complementary.

The statistic models were based on analysis of covariance (ANCOVA: generalised multiple linear regression for quantitative and qualitative variables). For more details and explanations about these quantitative analyses, see [START_REF] Osso | The structuring of air source heat pumps' prices in a retrofitting residential buildings market: what did I pay for?[END_REF]. This method was selected because it enables to assess the relative effect of each qualitative or quantitative variable tested on the explained variable and to distinguish the effects of variables that can be correlated. The prices of residential retrofits in the residential sector (i.e. for the samples analysed: mostly works in single-family homes decided by owner-occupiers) presented a large price dispersion (see relative interquartile range3 in Table 1) that was difficult to explain at first, even for fairly similar projects (e.g. boiler, insulation of attic spaces). We must noticed that we only studied efficient work (i.e. eligible for the French EEO4 and tax credit schemes) with relatively small performance differences between the different measures of the same type (e.g. small efficiency difference between the condensing boilers installed).

Results

The ANCOVA analyses based on the technical and main samples show that the price dispersion was partly explained by technical reasons (complexity of a renovation project) and/or economic reasons (product quality, organisational structures). Other reasons may also have come, among others, from the brand of products, the local competitive situation and the ability of households to pay.

Effects of technical variables

The statistical analyses showed that extensive technical variables (e.g. surface treated, number of windows) were the main reasons for the price variation in absolute terms (i.e. in € excluding VAT). Since we only studied efficient work (i.e. eligible for the French EEO and tax credit schemes) with relatively small performance differences, the energy performance variables (e.g., heat pumps' coefficient of performance -or thermal resistance) were considered as significantly explanatory of the price variation only for the modelling of external insulation works and the installation of an air/water HP.

Once the extensive technical dimensions5 had been neutralized via the price per unit for surfaces (in € excluding VAT /m²), the main variables that explained the price variations remained technical:

 Installed power (boilers and heat pumps) density, i.e. per heated floor area (kW/m²), surface treated (m²) for insulation (scale effect). The installed surface power density (kW/m²) is usually linked to the design depending on the energy needs of the dwelling. The greater the installed power per unit area, the higher the price. For insulation, as the area increased, the price per square meter decreased non-linearly due to the effect of fixed and variable costs (surface treated).  Individual technical characteristics (e.g. multi-split air/air heat pump, external wall insulation, etc.).

Economic effects

We studied socio-economic components impacting price changes with economic effects. For all the works, the geoclimatic zone 6 (H1, H2 or H3) impacted the price of the works. Energy efficiency retrofit works had a higher price in zone H1 than in zone H3. Zone H2 is between these two extremes or close to zone H1. It was difficult to interpret the origin of this gap easily but we must noticed that the effect of the climatic zone can be distinguished from other correlated variables (e.g. the installed power of heating systems in colder zone is likely higher than in warmer zone -see above). A possible explanation could be the willingness of households to pay that would be greater in areas with a harsher climate (zone H1) because heating costs are a proportionately larger share of the energy bill. Indeed, the potential income effect related to climatic zones should be captured at least partly by the variable "town's household income" but its effect remained small. The problem of competition between professionals and the types of work could not explain the existence of the gaps between climatic zones. Indeed, local wealth (identified through the town's household income (INSEE, 2016) as proxy for the income level of the household financing the works) had a small but positive significant effect on the price of works.

Another notable economic effect concerned the brands of heating systems. Name of brands of the installed equipment were available for thermal systems (HP, boilers) but could not be acquired for insulation work. The effect of brand alone accounted for one-third of the variance in the installation cost of a condensing boiler. As there is significant uncertainty associated with the effects of each brand, we are not really able to differentiate all brands beyond two groups of brands that are more or less expensive than the average. Moreover, some brands present no effect meaning that they are close to the average market price.

The effect of the commercial network7 to which the installer belonged (or did not) was variable and depended on the network itself, some having a positive impact on prices and others a negative effect. Membership in a commercial network therefore did not guarantee a lower price level than with an unaffiliated company; however non-affiliated companies were still the majority in the sample and in the market.

The increasing number of a company's employees is related to a higher price, with the exception of businesses without employees or very large companies (> 100 employees). The impact of the company's workforce seemed to have an upward effect on prices, with businesses with more workers having a higher price. Individual entrepreneurs formed an outlier as their prices were higher than these of slightly larger companies (1 to 6 employees). It was difficult to get comprehensive knowledge of companies without any employees. We should therefore be cautious about the generalization of our observations. Nevertheless, the upward effect of company size on the price could be explained by higher structural and management costs that might not compensate for possible bargaining power for lower equipment prices from wholesalers.

The impact of the business trades (NACE8 segment) was complex to study because companies only report in the INSEE database their main activity (or their historical activity) and it may have had nothing to do with the activity we were studying9 . In addition, because of the diversity of business segments (several dozen) and the sometimes similar effects, it is difficult to draw general conclusions about a particular sector. Nevertheless, certain business segments that seemed to be the least directly connected to renovation activity (services, wholesale trade, holding activities, home sales, etc.) had an upward effects on prices. Similarly, in certain types of work, there may have been be an upward effect on the price when the company was identified as performing work outside of a different category from the one studied (e.g. carpentry work for the installation of a heat pump, electrical installation for the installation of windows, etc.). This can be interpreted as risk hedging (the company adding an extra margin to carry out work it is not used to). There is also a difference between insulation work and thermal system work. These last cases were for the majority carried out in a single activity (NACE 4322B) corresponding closely to the works involved. On the other hand, for insulation work, there was a greater spread in the NACE activities identified, possibly due to the lower technical requirements.

Table 2: direction of effects (increasing: + ; decreasing: -) explanatory variables on the variation of the price of the retrofit in the "main sample" statistical models. In conclusion, it should be emphasized that it is difficult to understand the price changes of the residential renovation. At best, we can explain half of the variations by statistical models (see R² adj. in the Table 2 generally lowest than 0.5). This means that we were not able to capture enough information from those involved in price setting to explain all of it. However, for one of the best case (Figure 1) the coefficient of determination10 (R²adj) shows that half of the prices variation is explained with the available data. According to the statistical procedure11 , the main explaining variables are technical (blue ones) followed by economic variables (yellow and green ones). If we were able to record the technical data of the energy efficiency operation studied or the financial information from the professional performing the work (retrofit supply side), the information concerning the client (demand side) was not accessible. An unexplained part of price changes could therefore be sought from the household demand side or any other information not available in the quantitative study. This is why the qualitative study aimed at explaining in other ways the origins of the price variations that remained inaccessible for the moment.

Qualitative analysis

Methodology

The objective of the qualitative analysis was to understand the mechanisms for setting prices as they are practiced by professionals. In other words, it was about understanding how craftsmen make their estimates. Knowledge of the renovation companies' real-life practitioners made it possible to complement the quantitative technical and economic analyses. The methodology used was based on two field surveys conducted in 2017 through semi-structured interviews (duration: 1 to 2 hours) with professionals of the renovation works. In detail, these surveys consisted of:  16 interviews with retrofit professionals in Brittany and the Pays de la Loire region, North-West of France (plumber-heating specialists, electricians, roofers, insulation specialists, plasterers, carpenters, masons, interior fitters). Ages of the companies: from a few months to 36 years. Size: from a single craftsman working alone up to the commercial enterprise of 21 people with turnovers ranging from €70,000 to €1.8 million/a.  20 interviews with 15 companies in Alsace region (Bas-Rhin, North-East of France) with a focus on two main crafts: façades and space heating/electricity. Ages of the companies: from a few months to more than 100 years (mostly: over 10 years) and sizes: from a single craftsman working alone, to a company of 40 people with turnovers ranging from €150,000 to €3 million/a.

Most of the companies interviewed were involved in several markets: new constructions and renovations (energy-related or not), for individuals, architects, individual house builders, etc. Companies were very diverse with different "business models", stages of development and different outlooks, etc. Given this diversity, it is assumed that the sample is representative of the diversity of the companies active on the renovation markets.

The field survey of 31 building companies helped to understand professional pricing practices. Companies were asked about their search for clients, their site visits, estimate procedures and the prices charged. As a result of this investigation, we identified three additional explanations for the dispersion of renovation prices, thus complementing the quantitative In the next three subsections, we discuss each of these explanations in more detail: singularity of the project, characteristics of the customer as perceived by installers, and economic health of the company. Of course, in practice, these three aspects are much more interrelated than the presentation below might suggest. When preparing a cost estimate, the professional takes into account and constantly cross-references the job's characteristics. We propose this division for analytical purposes.

The singularity of the project

The singularity of the project means that each project has unique characteristics, which differentiated it from other projects and led craftsman to adjusting the price compared to the standard price. A first qualitative reason for price dispersion or variations is thus that renovation projects are not standard. Indeed, one of the major characteristics of private residential renovation is that each house, and therefore each renovation project, is unique: differences in construction methods (type of materials and implementation), size and accessibility, amenities, and work already done. The "technical" characteristics of the house, are complemented by the characteristics of the "buyer": their need, their project, their budget. Renovation remained up to now a "tailor-made" service12 : tailor-made for the house and tailor-made for the client. Finding and visiting the site was therefore crucial: the professionals we met never made a commercial proposal without being on site.

The on-site visit was essential because it allowed: identification of its accessibility, taking measurements, evaluating the complexity of the retrofit project, and identifying specific needs which could be transformed into ancillary services. It was also necessary to "understand" the house: the layout of rooms, where ducts could be laid, how to insulate the roof, how the house could develop (new living spaces in the attic or in the basement). This was reflected in the detail of the cost estimate, which according to the professionals, took on the shape of an actual technical study (energy audit) (particularly true in the case of the complete installation of a heating system, less true in the case of a simple change of boiler). The more complex the project, the more difficult it would be to prepare the cost estimate (it was not uncommon for it to take several hours). The detailed estimate was, beyond the cost justification (quantification), the formalization of the expertise of the craftsman through a technical study: assessing the house to suggesting solutions. In some cases, and especially when the professional feared the customer might share a cost estimate with competitors (see next section), the estimates were deliberately not very detailed.

Appraisal of the client

Appraisal of the client means here the "quality" of the client perceived by the craftsman on the basis of the maturity of its technical and financial project (which influenced the probability and timeliness of contract signature) and the cordial relations between the client and the professional (which may have had an impact on the margin and reputation of the professional).

When meeting customers, professionals seek to understand their personality, their need (that was not necessarily energy-related), the maturity of their project and their budget. An important point concerned the financing of the project (cash or on credit) because its maximum amount impacted the craftsman's future suggestions. The source of the customer contact was also important to determine if the customer was more focused on quality (local network, reputational effect leading to a "confidence premium") or on minimising costs (Internet, advertising). In the latter case, the customer tended to create a lot more competition between competing craftsmen, especially through the existence of digital intermediaries. Finally, the cordiality of the knotted relationship allowed the craftsman to anticipate the conduct of the project. A customer with whom contact is pleasant and who is not suspicious, but understanding, and who is in agreement with the professional's recommendations for the works is a guarantee of good progress on the renovation project. On-site "surprises" would not lead to unpleasant situations: the customer was likely to accept last-minute changes due to the actual conditions of the work or the professional adding materials not planned without recharging the customer. This aspect was doubly important for the work of the professional: not only during the work on site but also for their reputation, which in this market, was the main source of generating sales. Finally, the craftsman could decide to "ranking" their customers, which manifested itself in particular by sending cost estimates that were more or less detailed.

Understanding the singularity of the renovation project and assessing the client's worthiness led the professional to recommend a technical solution which, as we saw in the quantitative analysis, had a significant impact on the final price and not necessarily on energy performance. Indeed, several technical solutions could meet the same requirement: insulation under the roof, outside roof insulation (i.e. sarking), in attic spaces, etc. Or on a heating issue: condensing boiler, heat pump, biomass pellet boiler, etc. The craftsman therefore did not stipulate a single price but recommended or suggested a solution that corresponded to a certain budget for the work. The quote might include options like a type of paint but not two widely different options like natural vs synthetic insulation materials. The price line began to be developed at the time of the on-site visit, with the idea of a service that would allow a greater or smaller margin.

The economic health of the company

The economic health of the firm means here the greater or lesser need of the company to secure the contract, to adjust to market prices and the rigour of its management. This economic health, the dynamics of the market at the time of the site visit, and the local competitive pressure were all reasons which explained price variations. Indeed, even companies with high degrees of professionalism, that is to say, those organised (functional specialization) and using management tools, reported a variation in prices throughout the year. The same company would therefore charge different prices for comparable renovation projects depending on the season. In high season, when renovation projects were plentiful and the company had no trouble completing its workload schedule, prices would be higher (within the limit allowed by competitive pressure: a price that really was too high compared to competitors' offers would not "pass"). On the other hand, in the low season the company was ready to review its prices to ensure it won a job that it needed. The company's economic health played a similar role. A company facing economic challenges, which needed to get contracts to pay its employees, would be ready to reduce its margin to get a job. The quality of the company's management was also important. A company well equipped with management tools, which knew its costs, adjusted its margin but did not work at a loss. Some companies worked at a loss on some sites, and only discovered the problem at the end of the year, when they found themselves in deficit.

All these aspects had repercussions on the prices charged and the level of margins. Craftsmen approached their activity through their workload schedule ("have a good year") either by an empirical estimate of the number of renovation projects to be carried out or items of equipment to sell or on the basis of financial calculation via software tools and dashboards (annual turnover target). Except for some well-equipped and structured companies, two ways of calculating margins on materials and equipment were at work. The first way "started" with the cost of purchasing materials to which was added a margin that was standard for the trade, with "detailed" technical studies during the quoting process for complex services and detailed cost estimates. The second way "started" with the final selling price (selling pricegross margin = margin as a % of the selling price) which was standard for the trade that calculated per square meter with more standard services and simpler cost estimates.

Sometimes the initial quote included a percentage discount in the quotation (about 5%). This was regularly the case for the companies interviewed in the East of France and more rarely the case for the companies interviewed in the West of France (only for very standardised work and companies of a certain size with a dedicated sales department). This illustrated the role of local competitive pressure: prices were adjusted to what was done locally.

However, there was still the problem of including all the on-site risks, making the customers accept them and then charging them. The price did not include all the items to be taken into account: adjustment work that was not re-invoiced, undeclared work, any DIY13 work. Finally, the price and the margin varied depending on the season and the workload schedule, the customer, the supply costs, the site's accessibility. This is illustrated in the figure 2 In conclusion of the qualitative analysis, the sociological study has shown three additional explanations of the price variation of energy retrofit works (Figure 2). First, part of the price variation is due to the singularity of the project that is the unique characteristics of a project, which differentiated it from other projects and led craftsman to adjusting the price compared to the standard price. Second, we have shown that price variation also depended on the characteristics of the customer as perceived by installers: the maturity of the customer's project and the cordial relations between the client and the professional (which may have had an impact on the margin and reputation of the professional). A third explanation of price change is the economic health of the firm and the local competitive pressure, that is to say, the greater or lesser need of the company to secure the contract, to adjust to market prices and the rigour of its management.

Conclusion: the variability of the price reflects the diversity of companies and works

The joint quantitative and qualitative study of renovation bills allowed us to show the reasons for the great variability of the prices observed in the field. The results of the statistical study and the sociological study are complementary.

From a technical point of view, prices were explainable in large part, even if the local competitive dynamics, climatic zone and other conditions impact the price. Thus, 50% at best of the variability could be explained by (Table 4):

 technical reasons: product quality, dwelling size,  economic reasons: type of business,  marketing variables: brand name,  and climatic zone.

The quantitative analysis explained some types of work (heat pump, roof insulation and condensing boilers) properly, but others less well (windows, external insulation) (i.e. a low R²). We could hypothesize that when actions involved equipment that was insensitive to the singularity of the housing, prices were less variable and the model of construction of the price had little influence (margin on the material or project management margin). Products and activities that were not standardised, such as

Outlook: what growth pathways?

What are the implications of the dispersion of renovation prices, observed and explained in this article, with regard to the widespread expansion of energy efficiency retrofit? These implications are twofold.

In the first place, this article has shown that price dispersion is inherent in the current nonstandardization of private housing projects and that price dispersion has some objective reasons (i.e. technical). Other reasons that are not objective (i.e. explained by social factors) but understandable exist also.

This does not mean, however, that the whole price dispersion must be accepted and will lead to a status quo. We have indeed shown that there is room for rationalisation in the price of renovation that would certainly be likely to boost the market. Indeed, part of price dispersion is explained by the professional's perception of the customer's quality and the company's economic health.

These are two potential levers for price rationalization. On the one hand, by introducing systems that accelerate the client's project maturing, and informing and training the client about the energy efficiency retrofit (i.e. helping customers to better express their needs and understand the options recommended by the craftsmen; improving conditions for ensuring confidence between customers and craftsmen). On the other, helping professionals to better manage their businesses. One assumption could be that a customer that is better informed can better negotiate with a craftsman that have a good insight of his business to rationale his quotation.

In addition, to reduce the cost of work, studies on the energy renovation value chain and supply chain are necessary because some of the margins do not depend on the craftsman but to other entities (i.e. wholesaler, distributor and manufacturer).

As a result, price dispersion is not necessarily an absolute obstacle to the expansion of renovation but a currently unavoidable reality. In this case as a first step, it is more a question of working on the financing of the works than on their price. However, through standardization of practices and better business management, prices could be decreased but that is unfortunately not the current situation of the French retrofit market.

Lessons learnt from the study presented in this paper are very informative for the new plan for energy renovation recently released by the French Ministry [START_REF] Mtes | Plan de rénovation énergétique des bâtiments[END_REF]. This plan indeed includes some actions in line with the findings from the study. For example, actions n°4 and 11 of this plan aim at increasing the confidence that owners can have in the offers of renovation works, by promoting a single quality brand and by reinforcing and complementing the existing labelling and training schemes. The plan also announced the establishment of a national observatory of energy renovations. One of its missions will be to improve the knowledge of the renovations markets, and particularly offers of renovation works. One of the specific tasks mentioned in the plan is to build indicators of average prices per type of works. Findings from our study show that this task could be challenging.

In conclusion, it should be noted that the research described in this article did not address the issue from the clients' point of view: how do they choose their professionals? What is their propensity to pay more for a promise of quality? Bridging this knowledge gap would complement our analysis of the factors behind the dispersion of renovation prices and suggest additional ways of optimizing the market.

Disclaimer

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of their affiliations.

Figure 1 :

 1 Figure 1: Change in the coefficient of determination (R²adj = 0.52) according to the variable selected (stepwise procedure) for the air/air HP "technical sample" (price in €/m² excluding VAT). The segments show the coefficient of determination increase by the cumulative addition of a new variable.

Figure 2 :

 2 Figure 2: the difficulty of fixing the price of renovation works.

Table 1 :

 1 target prices (€ excluding VAT) of various types of work (main samples).

	Type of work (unit)	Average price	Median price	Relative interquartile range**	Share of Labour costs*	Share of ancillary costs*
	Air/air HP (€)	4,767	3,733	0.69	20%	9%
	Air/water HP (€)	14,300	13,211	1.11	12%	7%
	Domestic heating boiler (€)	4,400	3,864	0.58	17%	15%
	Attic (€/m²)	55	47	0.61	26%	22%
	Internal wall insulation (€/m²) External wall insulation (€/m²)	80 174	67 159	0.50	30% 30%	58% 35%
	Window (€/unit)	1,343	1,131	0.73	18%	-
	* Data from technical sub-sample: labour cost and ancillary costs are not cumulative.
	**The greater is the relative interquartile range, the greater the dispersion.

  : information not available. m² of insulated area. *Equipment size / extent of the works.

				Technical variables					Economic variables
	Type of work (unit)	adjusted R²	Extensive*	Performance	H1 climatic	zone	H3 climatic	zone	Business	segment	Trade	network	Town's	household	income	number of	employees
	Air/air HP (€)		0.70	+		+		-		+/-	+/-	+		+
	Air/water HP (€)	0.40	+	-	+		-		+/-	+/-				+/-
	Domestic boiler (€)	heating	0.32	+	n/a	+		-		+	-					+/-
	Attic insulation (€/m²)	0.36	-	n/a	+		-		+/-	+/-	+		+
	Internal/external wall insulation (€/m²)	0.51	-	n/a	+		-		+/-	+/-
	Window (€/unit)	0.12	-	n/a	+		-		+/-	+/-	+		+
	n/a

The invoice provides several technical information, beyond the efficiency of the measure, like area (m²), power (kW), the type of equipment installed (e.g. brand). The invoices analysed are from

2 Less detailed means that the technical information available are limited.

The relative interquartile range is equal to the difference between 75 th (Q3) and 25 th (Q1) percentiles divided by the median value.

EEO: Energy Efficiency Obligation.

We must noticed that for some equipment (e.g. boiler) there is no sizing as the power installed is generally in the order of 23 to 25 kW due to sanitary water heating (at the exception of 30 kW for larger houses).

H1: coldest climatic zone in France (mostly North and East of France); H2: West of France, H3: warmest climatic zone (mostly South-East of France).

Franchise network, craftsman affiliated to a brand…

Economic Activities in the European Community(Eurostat, 2008).

For example, a craftsman of which the main activity is windows installer (declared NACE 4332A -Carpentry and PVC work) could also install internal wall insulation (NACE 4329A -Insulation work) which is not his declared activity.

The R² adjusted (goodness of fit) is the proportion of the variance in the dependent variable that is predictable from the independent variables and penalized the statistic as extra variables are included in the model (Wikipedia).

The stepwise procedure is a method of fitting regression models in which the choice of predictive variables is carried out by an automatic procedure. In each step, a variable is considered for addition (forward selection) from the set of explanatory variables, adding the variable (if any) whose inclusion gives the most statistically significant improvement of the fit, and repeating this process until none improves the model to a statistically significant extent (Wikipedia).

Even if there are initiatives such as Energiesprong under development in the Netherlands, UK and France to standardize retrofit measures (http://energiesprong.eu). However, Energiesprong addresses buildings and types of works that are prone to standardization which is not representative of the private residential building stock in France.

Do It Yourself, the part of retrofit supported by the household to reduce the retrofit cost.

The price of trust (via word of mouth) would be a premium of

15% to 20% of the amount of the retrofit(Travauxlib, 2017).

International Energy Policy & Programme Evaluation Conference -Vienna, Austria

Acknowledgements

This project has received funding from ADEME under grant agreement No 1510C0040. We would like to thank the reviewers (moderator and teammates) for their comments which helped us to enhance this paper. We would also like to thank Marie-Laure Nauleau and Albane Gaspard (ADEME) members of the Steering Committee for this study.

windows (often tailor-made) or external insulation (a variable part linked to irregularities in the house and ancillary services) introduced more unexplained variability. Conversely, for more standard products such as boilers and attic insulation, the variability of unexplained ground conditions is smaller.

A determining factor in the price of the work lies in the installer's recommendations: what work should be done and with what material or equipment? With equal energy performance, these recommendations also have an effect on prices.

From the customer's point of view, the renovation market is marked by high uncertainty: technically complex, committing (substantial budget) and worrying (potential design defect or poor execution). Reputation and confidence are key. These points are taken into account in the price as a "confidence premium 14 ". The unexplained part of price setting could also be due to the supply characteristics that are not present in the invoice database, such as the "off invoice" (DIY) part.

On the installers' side, the price is fixed at the intersection of the perception of the appraisal of the customer, the management practices of the company (profit margin, workload schedule), and the adjustment to the local market price (Table 4). A good price from the installer's point of view is therefore the price that allows their company to survive or make profits and win new contracts (reputation effect).

In conclusion, observed prices may differ from the price that is objectively considered "correct" (i.e. on a purely technical basis) but this does not mean that prices are "unreasonable". Prices include qualitative dimensions: site accessibility, quality of work (meeting deadlines, cleanliness, etc.) that make them "fair" in practice. These dimension are not explicitly written on the quotation but are hidden behind technical items (e.g. larger margin on equipment) increasing price dispersion. Thus a merely technical reference price is not enough to determine the likely price of the renovation work.


[Données à caractère personnel] 7

Introduction

The primary aim of epilepsy surgery is to remove the epileptogenic zone (EZ), i.e. 'the minimum amount of cortex that must be resected (inactivated or completely disconnected)

to produce seizure freedom' (Rosenow and Lüders, 2001). In this context, intracranial EEG (iEEG) can be performed when non-invasively obtained data remain insufficiently concordant, when they are discordant or inconclusive, or when they suggest an early involvement of highly eloquent areas [START_REF] Jayakar | Diagnostic utility of invasive EEG for epilepsy surgery: Indications, modalities, and techniques[END_REF]. Such recordings aim not only at precisely identifying the cortical areas to be removed, but also at evaluating their functional integrity. This needs on the one hand the recording of spontaneous seizures, and on the other hand the use of cortical electrical stimulation (CES) to map eloquent cortical areas that will have to be spared during surgery.

Although the iEEG definition of the EZ mainly relies on the recording of spontaneous seizures (SS), some teams, mainly in France and Italy, routinely use CES during stereotactic iEEG (SEEG) recordings to aid in delineating the EZ, providing that the patient's typical electro-clinical pattern is produced [START_REF] Kahane | The Bancaud and Talairach view on the epileptogenic zone: a working hypothesis[END_REF][START_REF] Trébuchon | Electrical Stimulation for Seizure Induction and Functional Mapping in Stereoelectroencephalography[END_REF].

This approach, promoted by the Hospital Sainte Anne school [START_REF] Bancaud | Commentary: acute and chronic intracranial recordings and stimulation with depth electrodes[END_REF], is considered as a necessary complement of SS recording, particularly when spontaneous ictal discharges are widely extended from the onset, when they apparently arise independently from different brain structures, or when regions that are initially silent at seizure onset abruptly activate in the course of the ictal discharge. The clinical utility of CES-induced seizures (CESS), however, remains controversial and most of north-american centers using subdural electrodes do not rely on such information because they consider and CES-induced afterdischarges and seizures as a by-product of cortical mapping that can disrupt the procedure [START_REF] Bank | Characteristics and clinical impact of stimulation-evoked seizures during extraoperative cortical mapping[END_REF], may inaccurately localize cortical functions (Blume et al., 2004), and do not show consistent colocalization between the stimulation site and the SS onset area (Blume et al., 2004). This controversy is partly linked to the great variability in the methodologies used across centers, to the lack of a consensual definition of CESS, and to the differences in the conceptual approach to epilepsy surgery.

Suprisingly and despite decades of intra-and extraoperative CES procedures in epilepsy surgery candidates, only a few studies have investigated the relevance of CESS in clinical practice. In a recent review, 14 studies were identified during a 30 years period , of which 9 used SEEG electrodes, 3 intraoperative CES, and 2 subdural electrodes [START_REF] Kovac | Seizures induced by direct electrical cortical stimulation. Mechanisms and clinical considerations[END_REF]. Overall, the percentage of patients in whom seizures could be elicited varied from 37 to 100%, with a large predominance of CES-elicited auras. The concordance rate between the electrodes exhibiting CESS and those overlying the site(s) of SS onset, evaluated in only 6 of these 14 studies, varied from 26% to 100%, with the best results obtained in patients with focal cortical dysplasia or suffering from temporal lobe epilepsy [START_REF] Bernier | Electrical Stimulation of the Human Brain in Epilepsy[END_REF][START_REF] Chassoux | Stereoelectroencephalography in focal cortical dysplasia: a 3D approach to delineating the dysplastic cortex[END_REF][START_REF] Chauvel | Electrical stimulation with intracerebral electrodes to evoke seizures[END_REF][START_REF] Landré | Intérêt des stimulations électriques intracérébrales en stéréoélectroencéphalographie dans les épilepsies partielles[END_REF][START_REF] Schulz | Localization of epileptic auras induced on stimulation by subdural electrodes[END_REF][START_REF] Wieser | Comparative value of spontaneous and chemically and electrically induced seizures in establishing the lateralization of temporal lobe seizures[END_REF]. How the information obtained from CESS might influence seizure outcome was assessed in only one study, that did not show any differences according to whether CESS site(s) were included in the resection or not [START_REF] Schulz | Localization of epileptic auras induced on stimulation by subdural electrodes[END_REF].

Based on these existing data, it thus appear that further studies are needed to better evaluate the clinical and iEEG overlap beween SS and CESS, and to determine what is the precise added contribution of CESS over SS in terms of seizure outcome. The present retrospective study aimed at answering these issues in a series of 30 consecutive patients who underwent SEEG recordings at our institution. Whether general features might influence the information provided par CESS was also evaluated.

Patients and methods

Patients selection

Between October 2013 and November 2015, 32 patients suffering from drug-resistant focal seizures underwent a SEEG study at Grenoble-Alpes University Hospital as part of their presurgical evaluation. For the purpose of the study were selected the 30 patients in whom at least one complete spontaneous electro-clinical seizure was recorded during SEEG investigation.

Patients's characteristics

The 30 patients were all suffering from drug-resistant focal epilepsy, the operability of which could not be decided on the basis of non-invasive procedures only. These latter included in all cases high-resolution MRI, scalp-video-EEG monitoring, and neuropsychological tests. Some patients underwent also functional neuroimaging.

A summary of the patients' characteristics is given in Table 1. Briefly, there were 15 males and 15 females, whose mean age at SEEG investigation was 28 years (range 9-59 years).

Mean age at seizure onset was 15 years (range 0.5-38 years), and mean duration of epilepsy was 14 years (range 3-40 years). MRI demonstrated different kind of lesions in 21 patients, of whom 6 had previously undergone unsuccessful resective surgery before SEEG procedure.

MRI was negative in 9 cases.

SEEG investigation

Twelve to 18 (mean: 14.3) multicontact semirigid intracerebral electrodes were implanted in each patient in stereotaxic conditions, according to the SEEG methodology developed in our group [START_REF] Kahane | Invasive EEG in the definition of the seizure onset zone: depth electrodes[END_REF]. Electrodes placement and number was tailored in each individual depending on the suspected origin of seizures. Preoperative targeting was performed using 3-D T1 brain MRI computed with a stereotactic software (ROSA stereotactic assistance®), and using a stereotaxic and stereoscopic digitalized arteriography to determine avascular trajectories of the electrodes. Insertion of the electrodes (DIXI Medical, Besançon,

France; diameter of 0,8 mm; 10 to 18 contacts, 2 mm length, 1.5 mm apart) was guided by a robotic arm (Medtronic O-Arm®) that was connected to the stereotactic frame and driven by the stereotactic software. Electrodes contacts were visualized directly on post-implantation MRI, and/or after a computer-assisted matching of post-implantation CT-scan with a preimplantation 3D MRI.

SEEG recordings were conducted extra-operatively for about 2 weeks with reduced medication in 23 of the 30 patients, using an audio-video-EEG monitoring system (MicromedTreviso, Italy) that allowed to record simultaneously up to 128 contacts, with a sampling rate of 512 Hz and an acquisition band-pass filter between 0.1 and 200 Hz. Data were acquired using a referential montage, with a reference electrode chosen in the white matter. SEEG activity was displayed between contiguous contacts at different levels along the axis of each electrode, and interictal and ictal analysis of SEEG traces was done visually.

CES were performed for a few days during one to three hour sessions, according to our routine procedure [START_REF] Kahane | Electroclinical manifestations elicited by intracerebral electric stimulation ''shocks'' in temporal lobe epilepsy[END_REF]. The aim was to reproduce part or the totality of the ictal clinical symptomatology, and to localize functionally eloquent areas that had to be spared during surgery. Bipolar stimuli were delivered using a constant current rectangular pulse generator designed for a safe diagnostic stimulation of the human brain (Micromed, Teviso, Italy). Bipolar CES were performed at 1 Hz (pulse width: 1msec; ES duration: 40 sec)

and 50 Hz (pulse width: 0.5-1ms; ES duration: 5 sec), and applied between all contiguous contacts located in the cortex, with stepwise increasing intensities up to 5 mA and until clinical responses, after-discharges or seizures were obtained.

Following SEEG results, 17 patients had a left-sided, 10 a right-sided, and 3 a bilateral focal epilepsy (Table 1). The epilepsy was unilobar in 21 cases (frontal: 11, temporal: 8, insular: 2), multilobar in 6 (temporo-parietal: 2, temporo-central: 1, temporo-insular: 1, temporo-insuloopercular: 1, fronto-parietal: 1), bitemporal in 2, and bilateral multifocal in 1.

Surgery

Surgery, including radiofrequency thermocoagulation (RFTC), was performed in all but 3 cases, according to SEEG results (Table 1).

Data analysis

Spontaneous seizures

All SEEG-recorded SS were reviewed, but neither subclinical seizures, nor seizures in which auras occurred without any SEEG modification were kept for analysis.

The EZ was defined according to its electrophysiological definition, i.e. the ''site of the beginning and of the primary organization of the epileptic seizures'' (Munari and Bancaud, 1987). The EZ therefore included the seizure onset zone (the region exhibiting the first SEEG change that occurred prior to, or concomitant with, the clinical onset of the seizure) as well as the region of early seizure spread (that was arbitrarily defined as the region involved by the SEEG discharge within the first 20 seconds following the ictal onset). SEEG changes at seizure onset were classified, whatever possible, according to the seizure-onset patterns proposed by [START_REF] Perucca | Intracranial electroencephalographic seizure-onset patterns: effect of underlying pathology[END_REF].

The anatomical extent of the EZ was evaluated in each patient by the number of electrode contacts involved during the first 20 seconds of the SS. If different seizure patterns were recorded, all the contacts involved within the first 20 seconds, whatever the seizures, were included in the EZ.

Seizure semiology was analyzed according to a working definition of clinical phenomena derived from the classification of [START_REF] Lüders | Semiological seizure classification[END_REF]. Briefly, a total number of 6 core clinical signs were systematically evaluated, including aura, autonomic signs, loss of contact, simple motor signs, complex motor signs and negative phenomena. They were quoted as present or absent in each SS, and they were then compiled in a single list for all SS.

CES-elicited seizures

Only CES-induced electro-clinical seizures were analysed, and neither elicited isolated aura (without SEEG discharge), nor isolated after-discharges (without clinical accompaniment),

were considered in the present work.

CESS thus referred to electro-clinical events that occurred as an immediate result of CES, and in which both clinical signs and SEEG discharge outlasted the electrical stimulus. They were considered as habitual (non habitual) when elicited clinical manifestations were (were not)

recognized by the patient and/or his/her relatives.

The parameters used to elicit CESS were first evaluated. Then, the CESS onset patterns, anatomical extent of the elicited discharges, and CESS semiology were assessed using the same criteria than those used for SS analysis. Whether the CES location within or outside the EZ might influence the rate of CESS was also evaluated.

Comparison between SS and CESS

A rate of electrical concordance was calculated for each patient by comparing the extent of the EZ with the mean extent of all elicited discharges. Similarly, a rate of clinical concordance was evaluated in each patient by comparing the mean number of clinical signs observed during CESS with the list of SS clinical signs.

Still, whether other factors might influence the rate of electrical and/or clinical concordance was assessed. These factors included the age at seizure onset, epilepsy duration, MRI findings (negative versus positive), and epilepsy type (temporal versus extra-temporal).

CESS and outcome

All the post-operative MRI were reviewed to evaluate, for each patient, the percentage of CESS contacts that were located in the resective (or thermo-coagulated) area. This percentage was then compared with post-operative seizure outcome.

Other potential prognosis factors were also evaluated, including the number of CESS, the percentage of contacts that elicited CESS within the EZ, the SEEG LVFA pattern at CESS onset, and the rates of electrical/clinical concordance.

Statistics

We used Fisher's exact test for categorical data, and Mann-Whitney's U test or Spearman's correlation for continuous data. Significance was set at p ≤ 0.05.

Results

Twenty four of the 30 patients (80%) exhibited at least characteristics did not seem to differ from the ones of the 6 patients who did not present any CESS (Table 1). None of these later, however, were suffering from temporal lobe (TLE), as compared with 10 of the

The following sections will refer only to these 24 patients, who exhibited both SS and CESS. Twenty four of the 30 patients (80%) exhibited at least one CESS characteristics did not seem to differ from the ones of the 6 patients who did not present any (Table 1). None of these later, however, were suffering from temporal lobe (TLE), as compared with 10 of the 24 patients with CESS.

The following sections will refer only to these 24 patients, who exhibited both SS and CESS. CESS. Their general characteristics did not seem to differ from the ones of the 6 patients who did not present any (Table 1). None of these later, however, were suffering from temporal lobe epilepsy

The following sections will refer only to these 24 patients, who exhibited both SS and CESS. Spontaneous seizures (SS) (Tables 1 and2)

A total number of 402 SS (mean: 16.7/patient; range: 1-193) was recorded in the 24 patients.

Six to 74 contacts per patient were part of the EZ (mean: 29), which was temporal in 10 patients (mesial: 7, temporo-basal: 1, bitemporal: 2), frontal in 7 patients (mesial: 4, frontobasal: 2, lateral: 1), insular in 2 patients, and multilobar or multifocal in 5 patients.

Most SS started with a low-voltage fast activity (LVFA, n=270, 67%) (Figure 1a). The other seizure onset patterns included a fast discharge or spikes or polyspikes (FDS, n=68, 17%), a mixture of LVFA and FDS, (n=50, 12%), a rythmic spikes or spike-and-waves discharge (RSD, n=13, 3%), and a rythmic alpha-theta sharp activity (RSA, n=1, <1%).

CES-elicited electro-clinical seizures (CESS) (Tables 1, 2 and3 In comparison with SS, the elicited discharges started more frequently with a FDS (n=78, 65%) than with a LVFA (n=13 LVFA+FDS (n=5, 14%), and RSA (1, 1%).

Sixty nine of the 99 CESS (70%), and 13 of the 23 contact located within the EZ.

Electro-clinical comparison between

SEEG findings were available in all the 24 patients.

within the first 20 seconds of all the CESS (mean number/patient: 3.2 (70.4%) (mean number/patient: 0 concordance varied from 0 to 100% per patient, w than 1Hz CES did (3/22, 13.6%), but they were also more prone after 50 Hz CES versus 1/9 after 1 Hz CES, p=0.68, Fisher's exact

In comparison with SS, the elicited discharges started more frequently with a FDS (n=78, 65%) than with a LVFA (n=13, 16%) (Figure 1bc). The other ictal patterns i

, and RSA (1, 1%). Elicited RSD was never observed. between SS and CESS (Tables 2 and3) Overall, 1312 contacts were involved -48), of which 854 48) overlapped with the EZ. The rate of electrical ith an average of 77.4%. This concordance rate was even better when considering only the CS, with a mean of 86.7% per patient (30-100%) (Figure 1abc).

SEEG
Seizure semiology was available in all but one patients, in whom the video material of the unique seizure recorded could not be visualized (#19). For the remaining 23 patients, 126 (85.1%) of the 148 clinical signs identified during CESS (1-21/patient) were concordant with those identified during SS. As for electrical findings, the rate of clinical concordance was higher for CS (n=15 patients, mean: 95.3%, range: 25-100%) than for the whole group of CESS (mean: 85.1%, range: 0-100%).

No statistically significant association was found between the rates of electrical/clinical concordance and (i) the age at seizure onset (p=0.14/0.09, Spearman's correlation), (ii) epilepsy duration (p=0.44/0.33, Spearman's correlation), (iii) MRI findings (p=0.67/0.33, Mann-Whitney's U test), and (iv) epilepsy type (p=0.15/0.67, Mann-Whitney's U test).

CESS and seizure outcome

Overall, the percentage of contacts that elicited seizures and which were located in the resective (or thermo-coagulated) area varied from 0% to 100% per patient (mean: 43.7%) for all CESS, and from 0% to 100% (mean: 48%) for CS only. These percentages did not significantly correlated with the post-operative seizure outcome (respectively p=0.24 and p=0.74, Mann-Whitney's U test).

Otherwise, no statistically significant association was found between seizure outcome and (i)

the number of CESS (p=0.26, Mann-Whitney's U test, (ii) the percentage of contacts that elicited CESS within the EZ (p=0.24, Mann-Whitney's U test), (iii) the SEEG pattern of LVFA at CESS onset (p=1, Fisher's exact test), and (iv) the rates of electrical/clinical concordance (p=0.96/0.45, Mann-Whitney's U test). Low voltage fast activity (LVFA) involving first the amygdala (*), followed by a mixture of LVFA with a fast discharge of spikes within mesial temporal structures 12 seconds later (arrow). The discharge then propagate to the insula an operculum; STG: superior temporal gyrus; MesioT: mesio-temporal structures; T neocortex: temporal neocortex. EKG: electrocardiogram. stimulated seizure, anterior hippocampus, 3mA (same patient as in Figure 1a). The spatial distribution and shape of the elicited discharge is similar to the spontaneous one. Clinical semiology is the same. Fop: frontal operculum; STG: superior temporal gyrus; MesioT:

electrocardiogram.

Low voltage fast activity (LVFA) involving first the amygdala (*), followed by a mixture of LVFA with a fast discharge of spikes within mesial temporal structures 12 seconds later (arrow). The discharge then propagate to the insula and temporal neocortex. Fop: frontal temporal structures; T neocortex: temporal neocortex. EKG: electrocardiogram.

The spatial distribution and shape of the elicited discharge is similar to the spontaneous one. Clinical semiology is the same. Fop: frontal operculum; STG: superior temporal gyrus; MesioT: mesio-temporal structures; T Figure 1c. 50Hz-stimulated seizure, entorhinal cortex, 2mA (same patient as in Figure 1ab). elicited seizure is obscured by artefacts, the SEEG pattern consists from the onset in a fast discharge of spikes, and seizur discrepencies (loss of contact from the onset and amnesia of the episode).

Figure 1d: 50Hz-stimulated seizure, temporal pole, 2mA: patient referred a chest warmth recognized as a part of her habitual seizure. The afterdischarge involves the mesi the anterior insula and the temporal neocortex with different electrical patterns than the spontaneous one, more tonic on the temporal pole (arrow). stimulated seizure, entorhinal cortex, 2mA (same patient as in Figure 1ab). As compared with the spontaneous seizure (Fig. 1a), the initial part of the elicited seizure is obscured by artefacts, the SEEG pattern consists from the onset in a fast discharge of spikes, and seizure spread faster, therefore explaining some clinical crepencies (loss of contact from the onset and amnesia of the episode).

20

stimulated seizure, temporal pole, 2mA: the patient referred a chest warmth recognized as a part of her habitual seizure. The afterdischarge involves the mesial temporal structures, the anterior insula and the temporal neocortex with different electrical patterns than the spontaneous one, more tonic on the As compared with the spontaneous seizure (Fig. 1a), the initial part of the e spread faster, therefore explaining some clinical : the afterdischarge involves the right amygdala and the right hippocampus and in a lesser extent the right insula, as in the second part of the spontaneous seizure.

Discussion

Since the pioneering works of Penfield and Jasper [START_REF] Penfield | Epilepsy and the functional anatomy of human brain[END_REF], CES has appeared as a powerful technique to study network mechanisms in epilepsy, including functional mapping of brain functions, estimation of functional connectivity, assessment of cortical excitability, and elicitation of seizures [START_REF] David | Studying network mechanisms using intracranial stimulation in epileptic patients[END_REF]. This later aspect, however, has been poorly investigated [START_REF] Kovac | Seizures induced by direct electrical cortical stimulation. Mechanisms and clinical considerations[END_REF] and the main purposes of the present work were to evaluate how CESS and SS overlapped, both electrically and clinically, and whether the information obtained from CESS might help for the surgical decision. To this aim, attention was focused on electro-clinical events in order to rule out all the ambiguities raised by the elicitation of isolated auras (i.e., auras that are generated during the stimulation without concomitant nor further iEEG change), or by the induction of isolated afterdischarges (i.e., asymptomatic discharges of spikes, polyspikes or sharp waves that are directly related to and outlast CES, without evolving in frequency and spatial location).

CESS is not a rare phenomenon

In a recent review, the rate of CESS was shown to vary from 37 to 100%, depending on the type of CES procedure, on the criteria used to define CESS, and on the studied population [START_REF] Kovac | Seizures induced by direct electrical cortical stimulation. Mechanisms and clinical considerations[END_REF]. Our study, conducted in an heterogenous population of consecutive patients, confirms that CESS ressembling to SS (i.e., electro-clinical CESS) can be found in a vast majority of patients submitted to SEEG recordings (24/30 patients, 80%), a rate which is close to the overall rate of CESS (343/449 patients, 76%) found in other studies conducted by means of intracerebral electrodes [START_REF] Bernier | Electrical Stimulation of the Human Brain in Epilepsy[END_REF][START_REF] Chassoux | Stereoelectroencephalography in focal cortical dysplasia: a 3D approach to delineating the dysplastic cortex[END_REF][START_REF] Chauvel | Electrical stimulation with intracerebral electrodes to evoke seizures[END_REF][START_REF] Halgren | Mental phenomena evoked by electrical stimulation of the human hippocampal formation and amygdala[END_REF][START_REF] Kahane | Electroclinical manifestations elicited by intracerebral electric stimulation ''shocks'' in temporal lobe epilepsy[END_REF][START_REF] Landré | Intérêt des stimulations électriques intracérébrales en stéréoélectroencéphalographie dans les épilepsies partielles[END_REF][START_REF] Munari | Intracerebral low frequency electrical stimulation: a new tool for the definition of the "epileptogenic area"?[END_REF][START_REF] Wieser | Comparative value of spontaneous and chemically and electrically induced seizures in establishing the lateralization of temporal lobe seizures[END_REF]. By comparison, the overall rate of CESS observed intraoperatively [START_REF] Salanova | Occipital lobe epilepsy: electroclinical manifestations, electrocorticography, cortical stimulation and outcome in 42 patients treated between 1930 and 1991. Surgery of occipital lobe epilepsy[END_REF]Salanova et al., 1995a,b) or using subdural electrodes [START_REF] Salles | Subdural recording and electrical stimulation for cortical mapping and induction of usual seizures[END_REF][START_REF] Schulz | Localization of epileptic auras induced on stimulation by subdural electrodes[END_REF] has been shown to be much lower (65/173, 38%), a finding that might be related to the use of electrodes that penetrate the cortex rather overlay it, as well as to the use of bipolar CES which delivers more localized current flows than unipolar CES does [START_REF] Nathan | Determination of current density distributions generated by electrical stimulation of the human cerebral cortex[END_REF].

As showed by others [START_REF] Landré | Intérêt des stimulations électriques intracérébrales en stéréoélectroencéphalographie dans les épilepsies partielles[END_REF], our study also found that the temporal lobe was more sensitive than the frontal lobe for eliciting CESS, since all of the 10 stimulated TLE patients (of whom 8 were suffering from mesio-TLE) exhibited CESS, as compared with 7 of the 10 patients with FLE (see Table 1). Additionnally, CES of the insular lobe resulted in CESS in the 2 patients stimulated so far. Limbic structures therefore appear as particularly responsive to CES, which may in turn lead more frequently to NHS, as suggested by our results (all the NHS were elicited either in TLE or ILE patients).

Previous studies have showed that a large percentage of CESS clinically resulted in auras, that could be associated or not with iEEG changes [START_REF] Halgren | Mental phenomena evoked by electrical stimulation of the human hippocampal formation and amygdala[END_REF][START_REF] Kahane | Electroclinical manifestations elicited by intracerebral electric stimulation ''shocks'' in temporal lobe epilepsy[END_REF][START_REF] Salanova | Occipital lobe epilepsy: electroclinical manifestations, electrocorticography, cortical stimulation and outcome in 42 patients treated between 1930 and 1991. Surgery of occipital lobe epilepsy[END_REF]Salanova et al., 1995a,b;[START_REF] Schulz | Localization of epileptic auras induced on stimulation by subdural electrodes[END_REF]. Most were elicited from the temporal lobe [START_REF] Halgren | Mental phenomena evoked by electrical stimulation of the human hippocampal formation and amygdala[END_REF][START_REF] Kahane | Electroclinical manifestations elicited by intracerebral electric stimulation ''shocks'' in temporal lobe epilepsy[END_REF] or from the posterior cortex [START_REF] Salanova | Occipital lobe epilepsy: electroclinical manifestations, electrocorticography, cortical stimulation and outcome in 42 patients treated between 1930 and 1991. Surgery of occipital lobe epilepsy[END_REF]Salanova et al., 1995a,b). CS were less frequent and were observed in any locations, in particular when stimulating the frontal lobe [START_REF] Bancaud | Generalized'' epileptic seizures elicited by electrical stimulation of the frontal lobe in man[END_REF]. Using more strict criteria for defining CESS, we also found a large predominance of auras (77%) as compared with CS (23%). This over-representation of auras were found in all forms of epilepsies, except in MLE.

Whereas literature has showed that most CESS were elicited using high frequency (50-60Hz) CES, a few studies have reported the interest to use low frequency (1Hz) stimulation to elicit seizures [START_REF] Chassoux | Stereoelectroencephalography in focal cortical dysplasia: a 3D approach to delineating the dysplastic cortex[END_REF][START_REF] Chauvel | Electrical stimulation with intracerebral electrodes to evoke seizures[END_REF][START_REF] Kahane | Electroclinical manifestations elicited by intracerebral electric stimulation ''shocks'' in temporal lobe epilepsy[END_REF][START_REF] Landré | Intérêt des stimulations électriques intracérébrales en stéréoélectroencéphalographie dans les épilepsies partielles[END_REF][START_REF] Munari | Intracerebral low frequency electrical stimulation: a new tool for the definition of the "epileptogenic area"?[END_REF]. 1Hz CES, indeed, allows a better visualization of the SEEG recording at the onset of the induced discharge and during the stimulation itself (see Figure 1b), though with a more uncertain effectiveness [START_REF] Kahane | Electroclinical manifestations elicited by intracerebral electric stimulation ''shocks'' in temporal lobe epilepsy[END_REF][START_REF] Munari | Intracerebral low frequency electrical stimulation: a new tool for the definition of the "epileptogenic area"?[END_REF].

Our results confirms that 50Hz CES was more prone than 1Hz CES to elicit CESS (78% versus 22%), especially for CS. However, 50Hz CES also accounted of most NHS (89%), which could thus limit its utility.

Are CES-induced seizures similar to the spontaneous ones?

A few studies have tried to evaluate the electrical and/or clinical similarities between CESS and SS, with an estimation of the concordance rate that varied between 26% and 100% [START_REF] Bernier | Electrical Stimulation of the Human Brain in Epilepsy[END_REF][START_REF] Chassoux | Stereoelectroencephalography in focal cortical dysplasia: a 3D approach to delineating the dysplastic cortex[END_REF][START_REF] Chauvel | Electrical stimulation with intracerebral electrodes to evoke seizures[END_REF][START_REF] Landré | Intérêt des stimulations électriques intracérébrales en stéréoélectroencéphalographie dans les épilepsies partielles[END_REF]Schultz et al., 1997;[START_REF] Wieser | Comparative value of spontaneous and chemically and electrically induced seizures in establishing the lateralization of temporal lobe seizures[END_REF]. Data analysis, however, face with many difficulties such as the lack of information on the number of stimulated electrodes [START_REF] Bernier | Electrical Stimulation of the Human Brain in Epilepsy[END_REF][START_REF] Chassoux | Stereoelectroencephalography in focal cortical dysplasia: a 3D approach to delineating the dysplastic cortex[END_REF][START_REF] Chauvel | Electrical stimulation with intracerebral electrodes to evoke seizures[END_REF][START_REF] Landré | Intérêt des stimulations électriques intracérébrales en stéréoélectroencéphalographie dans les épilepsies partielles[END_REF][START_REF] Wieser | Comparative value of spontaneous and chemically and electrically induced seizures in establishing the lateralization of temporal lobe seizures[END_REF], CES parameters [START_REF] Wieser | Comparative value of spontaneous and chemically and electrically induced seizures in establishing the lateralization of temporal lobe seizures[END_REF], type of epilepsy [START_REF] Bernier | Electrical Stimulation of the Human Brain in Epilepsy[END_REF], iEEG changes [START_REF] Schulz | Localization of epileptic auras induced on stimulation by subdural electrodes[END_REF], and type (auras versus complete seizures) of CESS [START_REF] Bernier | Electrical Stimulation of the Human Brain in Epilepsy[END_REF][START_REF] Chassoux | Stereoelectroencephalography in focal cortical dysplasia: a 3D approach to delineating the dysplastic cortex[END_REF][START_REF] Chauvel | Electrical stimulation with intracerebral electrodes to evoke seizures[END_REF][START_REF] Landré | Intérêt des stimulations électriques intracérébrales en stéréoélectroencéphalographie dans les épilepsies partielles[END_REF][START_REF] Wieser | Comparative value of spontaneous and chemically and electrically induced seizures in establishing the lateralization of temporal lobe seizures[END_REF].

Still, some studies evaluated the concordance rate only in terms of seizure laterality [START_REF] Wieser | Comparative value of spontaneous and chemically and electrically induced seizures in establishing the lateralization of temporal lobe seizures[END_REF], or in specific situations such as focal cortical dysplasias [START_REF] Chassoux | Stereoelectroencephalography in focal cortical dysplasia: a 3D approach to delineating the dysplastic cortex[END_REF].

Our study, despite some limitations, compared carefully both electrical and clinical correlates of SS and CESS. It showed that a strong electrical (77.4%) and clinical (85.1%) concordance with SS did exist for the whole group of CESS, that was even better (86.7% and 95.3%, respectively) after having excluded the elicited auras which were likely to activate only part of the EZ. This high rate of electro-clinical concordance, which was neither influenced by the age at seizure onset, duration of epilepsy, MRI data, and epilepsy type, therefore suggests that CES can reactivate accurately the cortical areas involved in spontaneous ictogenesis, and thus could be reliable enough to define the EZ. This assumption, however, must be softened based on the following elements: i) we chose arbitrarily the first 20 seconds of SEEG discharges to account for the extent of the EZ, which prevented us to analyse the whole seizures evolution;

we thus have possibly missed some late discordances between SS and CESS, or late activations of initially silent areas that were more relevant than those occurring as the immediate result of CES (Figure 2a,b) ii) As compared with SS, which started more frequently with a LVFA (i.e., the most common iEEG seizure onset pattern, see [START_REF] Singh | Ictal onset on intracranial EEG: Do we know it when we see it? State of the evidence[END_REF], CESS started more frequently with a FSD, even when they involved the same anatomical sites (Figure 1c,d); the way neural synchronization is produced could be therefore different in SS and CESS, although providing similar information about the spatial organisation of the EZ; iii) 30% of CESS and 43.5% of CS were elicited from a cortical region located outside the EZ, which can limit the utility of CESS for defining the extent of the resection; worse results were found by [START_REF] Jacobs | Value of electrical stimulations and high frequency oscillations (80-500Hz) in identifying epileptogenic areas during intracranial EEG recordings[END_REF]: they found a maximum of 34% of stimulated contacts inducing an ictal response and located in the SOZ. On the other hand, interpretation may be less straightforward, and analysis of CESS must take into account the way the ictal discharge is generated, both spatially and temporally, rather than to simply consider that the seizure onset zone lies where the seizure is produced [START_REF] Trébuchon | Electrical Stimulation for Seizure Induction and Functional Mapping in Stereoelectroencephalography[END_REF]; iv) 9/99 CESS were reported by the patients as non habitual, of which only 3 definitely showed unusual electro-clinical patterns after having reviewed the previously recorded episodes; the rate of such 'false positive' seizures therefore remains low (3%), but clinicians should be aware that such episodes do exist, especially in mesio-temporal lobe structures and when applying 50Hz CES; whether they are only a by-product of CES, or whether they need an abnormal underlying hyperexcitable cortex to be elicited remains debatable.

Can CES-elicited seizures contribute in improving surgical outcome ?

Despite a strong electro-clinical concordance between CESS and SS, the resections that included CESS-eliciting sites did not lead to any superior outcome, compared to resections that did not include these sites, as already showed in another study [START_REF] Schulz | Localization of epileptic auras induced on stimulation by subdural electrodes[END_REF].

CESS-eliciting sites, however, were fully resected in only a few patients of our series (4/24), so that the prognostic significance of removing CESS-eliciting sites cannot be definitely ruled out. 30 % of CESS and 43.5% of the CS were induced by a stimulation performed outside of the epileptogenic zone. This finding probably reflects the existence of cortical regions more extended than the considered epileptogenic zone which could participate in the seizure production. The limits of this region and the consequences of its resection on the post surgical prognostic were not evaluated. However, its lack of consideration could explain the recurrence of seizures after a transient post operative seizure-free period.

Finally, no association was found between the electroclinical correlations and the post operative outcome (neither electrical p=0.96 -nor clinical p=0.45). The epileptogenic zone appeared not to be better identified with a higher correlation rate. In our study, the small size of the sampling doesn't enable us to draw any conclusions. However, a high number of seizures was not associated to a worse prognostic, demonstrating that CESS do not disturb the presurgical evaluation and the cortical mapping, as it was assumed by [START_REF] Bank | Characteristics and clinical impact of stimulation-evoked seizures during extraoperative cortical mapping[END_REF].

Merci à Lorella pour ces longues heures de lecture de SEEG, humoristiques d'un côté (« comme un malade! »), et source d'inspiration de l'autre, comme peut l'être votre personnalité, à la fois maternelle et directive. On en a souvent besoin. Merci d'avoir compris que mettre en avant les qualités des personnes permet de soutenir, rassurer et faire avancer.

Merci à Philippe pour ses visites inspirantes et son humour décalé, dont nous avons souvent besoin pour soulager la pression. Ce fut un honneur de travailler avec vous, le soutien moral dont vous nous faites preuve est précieux. Merci également pour l'inspiration clinicienne, la dyschronométrie, l'aphasie anomique, l'akinésie de l'AMS. C'est tout ce dont nous avons besoin pour nous rappeler pourquoi nous pratiquons la neurologie. L'apprentissage de l'urinal compartimenté pourra évidemment aussi nous être utile… A la Neurologie : Tout d'abord merci à Pierre Marie Gonnaud qui m'a donné le goût de la neurologie, et à Vincent Tarel qui a pris la suite. Pour leur générosité et gentillesse démesurées.

A mes chefs tant appréciés :

Tout d'abord à Anne Sophie Job, dont j'aurais voulu être la petite soeur, je me contenterai d'être ton camionneur, merci pour ton calme rassurant et ton intégrité, ta capacité à mettre les gens en valeur, merci aussi de n'avoir pas (trop) peur de montrer tes faiblesses. Tu es notre exemple à tous et j'espère que tu le sais.

A Elena Moro, notre maman de la neuro. Merci pour votre personnalité parfois déconcertante et le souci que vous avez pu mettre pour notre formation. Merci aussi pour ce restaurant du 1 er semestre, qui a contribué au fait que je continue la médecine.

A Mathieu Vaillant, pour sa gentillesse, et son partage, ses remises en question perpétuelles.

A Olivier Casez pour avoir été présent et m'avoir tant rassurée, et prolongé les contre visites humoristiques où avec un point d'honneur à ne pas écouter. Toc toc.

A Gérard Besson, pour sa personnalité et son grand coeur même s'il le cache bien parfois.

A Olivier Detante pour sa disponibilité au milieu de la nuit pour les thrombolyses improbables, et Isabelle Favre pour son accessibilité et sa gentillesse.

A Marie Barré et Julien Gere, pour ce semestre mémorable, plein de chocolat et de coca cola, de débats anti/pro féministes, et perchés dans la galaxie des spice girls. On évitera les thrombolyses à H+7 la prochaine fois Julien.

A l'équipe d'infectiologie de Chambéry, Emmanuel Forestier, Olivier Rogeaux, Claire Lecomte, Claire Marie Dutrop, et Nastasia El Zeenni dont j'ai tant apprécié l'humanité.

A Louise Cavat, qui a tellement embelli mes gardes, à la fois par sa bonne humeur, son professionnalisme, et ses fromages.

A toutes les équipes hospitalières, dévouées au service des patients, que je respecte tant et qui font un travail si difficile au quotidien, merci pour les prescriptions rattrapées, et votre compréhension dans les moments difficiles.

A mes cointernes,

A Marie, merci d'être là quand on en a besoin, pour ta bonne humeur, et ta nonchalance qui me font tellement de bien, je suis heureuse d'avoir partagé cette période de nos vies avec toi. Merci aussi à Alexis, son humour sarcastique incomparable, et le winch bien sûr.

A Pauline, pour ce semestre difficile, et les semaines de DU, ton exigence a pu me pousser vers le haut, même si je pense qu'elle pourrait être revue à la baisse parfois, tant pour toi que pour les autres, et dans laquelle je me reconnais trop souvent.

A Clem pour sa gentillesse profonde, « un peu de mystère c'est bien parfois », et Seb pour les potins, et le soutien rassurant de celui « qui y est déjà passé ». A Jérémie, avec un « e » merci pour ton savoir vivre, et ta bonne humeur, à Fanny et Anne, les accolithes si généreuses et humaines par nature, à Guilaume l'être sensible de la neuro, à Lucie et Hélène avec qui j'aurais voulu partager plus, à Giovanni, pour sa curiosité envers tout et tous, Sara pour ce semestre difficile pour moi, merci d'avoir supporté mes sauts d'humeur, à Loïc, Hugo, pour leur calme tranquille, et à Thomas pour avoir forcé tout le monde à manger à l'heure! A Victor Cubillé, Anne Laure Destrem, et Chloé Moulin pour ce semestre à Chambéry mémorable… A ma famille, Plus particulièrement à ma mère qui m'a tant soutenue, et a vécu autant que moi les moments difficiles, de la P1 à l'accident de voiture pendant l'internat. Merci de l'exemple que tu me montres chaque jour, de tolérance avant tout. Les années toutes les deux n'ont pas toujours été roses, et pourtant elles sont d'autant plus lumineuses que tu les as éclairées de ta philosophie et ton amour, mais pour tellement d'autre chose encore. Merci aussi de l'exemple de femme indépendante que tu représentes. Malgré mes tentatives, je ne le suis probablement pas autant que toi.

A Franck, que j'aime tant, un autre exemple dans ma vie, de simplicité, de courage et d'humilité, tu as été un pilier dans la tempête. Merci d'avoir embelli nos vies, à maman et à moi.

A Claude et Catherine, merci de votre présence votre soutien et votre amour, je pense que vous pouvez arrêter de croire qu'il faut encore rattraper le temps perdu à présent. A mon frère Paul, dont je suis si fière, de son ouverture envers les autres, sa capacité à apprécier sincèrement n'importe quelle attention, son ingéniosité et sa curiosité. Je vous aime fort.

A Gérard pour son amour et son éducation, se perpétrant malgré l'absence et l'incompréhension de mes choix de vie, merci pour m'avoir poussée au début, et tenté de me ralentir à la fin, merci pour les bain-douches, les cours de math, de dessin, pour la musique classique et tout le reste... A Luan et Neil Vinh, pour ne pas m'avoir oubliée, et pour la fuséebouteille ! Je souhaite de tout coeur faire d'avantage partie de vos vies.

A mes grands parents, Yvonne et Guy, pour leur amour et leur soutien inconditionnel. Merci pour les allers-retours à la fac et les repas chronométrés pendant les révisions. Les révision d'histoire et merci mamy pour ton énergie et ton amour, inépuisables, comme tes recettes de cuisine.

A ma marraine Cath, pour tout ce que tu es, ton humilité, ton soutien, ton amour et ta présence.

A mamy Helga, d'avantage ma grand-mère que bien d'autre. Merci pour ton soutien malgré l'absence, pour tes histoires du soir et les semaines de vacances, les coccinelles sur la neige. On ne peut pas le dire à toutes les grandes mères mais toi oui : merci d'être ma mamy.

A tous mes cousins cousines, et oncles et tantes, si nombreux et si présents dans ma vie, pour leur soutien et leur bonne humeur.

A Béa pour son côté décalé et féministe, ses plans foireux, et son ouverture sur le monde qui m'a beaucoup appris, et l'importance qu'elle met à être présente dans ma vie. A Elodie pour sa bonne humeur, son insistance téléphonique et son hippocampe surnaturel. A Chris, ma maman de substitution pour certaines périodes de ma vie. A mamy Dedette, pour ton émotivité à toute épreuve, et pour le mois à l'usine… Aux Bozons, pour m'avoir accueillie parmi les leurs, et avoir également supporté mes heures de travail, pour leur amour des montagnes, et toutes les petites attentions.

A mes amis :

A Léa, que je respecte tant, merci pour ton amitié sans faille, et ton exigence qui m'ont poussée vers le haut. Je sais que nous allons encore partager tant de chose encore, tant sportives que familiales… Je n'oublie pas Jason et Laloum qui me font tant rire. Si vous pouviez être un tout petit moins macho, je vous aimerais encore plus… A Féréole, ma zouev, les 2 distraites de service, merci pour tous les moments passés et futurs partagés, merci d'être aussi bon public, et de l'importance que tu accordes à notre amitié et à la vie en générale.

A Manu pour les révisions de l'internat surtout, et son amitié, ses préoccupations de fille qui m'autorise à l'être aussi un peu et Clem, pour les rigolades, et le rosé, sa présence n'importe quand si ça ne va pas.

A Camila pour son côté dégenté, les soirées lycéennes, les vacances au Brésil, les hébergements à Paris, et Julia et Maud, dont l'amitié compte tellement pour moi.

  correlation between seizures induced by direct electrical cortical stimulation and spontaneous seizures: relevance to define the epileptogenic zone THÈSE PRÉSENTÉE POUR L'OBTENTION DU TITRE DE DOCTEUR EN MÉDECINE DIPLÔME D'ÉTAT TARDY Nastasia Thèse soutenue publiquement le 20 octobre 2017 à la Faculté de médecine de Grenoble, devant un jury composé de: Monsieur de Professeur Philippe Kahane, Président du jury Monsieur le Professeur Fabrice Bartolomei Monsieur le Professeur Stéphan Chabardes Monsieur le Professeur Olivier David Monsieur le Professeur François Dubeau Madame le Docteur Lorella Minotti, directrice de thèse L'UFR de Médecine de Grenoble n'entend donner aucune approbation ni improbation aux opinions émises dans les thèses ; ces opinions sont considérées comme propres à leurs auteurs.

  experienced at least one complete CES-elicited electro-clinical seizure are highlighted in grey (n=16). Pt: patient; SS: spontaneous seizures; EZ: epileptogenic zone; CESS: electro-clinical seizures elicited by CES tion); CS: complete electro-clinical seizures elicited by CES; * no video material 15

  clinical seizures. Patients who clinical seizure are highlighted in grey (n=16). Pt: clinical seizures elicited by CES clinical seizures elicited by CES; * no video material

  CES: cortical electrical stimulation; CESS: electro elicited by CES; CS: complete electro seizure elicited by CES; * 5 (in 5 pts) were part of auras, and 4 (in 4 pts) were part of CS; ** 5 (in 5 pts) were part of auras, and 3 (in 3 pts) were part of CS; *** this event was part frontal lobe epilepsy; ILE: insular lobe epilepsy; MLE: multilobar/multifocal epilepsy.

(

  70%), and 13 of the 23 CS (13/23, 56.5%), . General characteristics of stimulation-induced electro-clinical seizures. Pts: patients; n°: number; CES: cortical electrical stimulation; CESS: electro-clinical seizure elicited by CES; : aura: electro elicited by CES; CS: complete electro-clinical seizure elicited by CES; NHS: non habitual electro ted by CES; * 5 (in 5 pts) were part of auras, and 4 (in 4 pts) were part of CS; ** 5 (in 5 pts) were part of auras, and 3 (in 3 pts) were part of CS; *** this event was part of CS; TLE: temporal lobe epilepsy; FLE: frontal lobe epilepsy; ILE: insular lobe epilepsy; MLE: multilobar/multifocal epilepsy.

  findings were available in all the 24 patients. Overall, 1312 contacts were involved within the first 20 seconds of all the CESS (mean number/patient: 3.2-(70.4%) (mean number/patient: 0-48) overlapped with the EZ. The rate of electrical concordance varied from 0 to 100% per patient, with an average of 77.4%. This concordance 17 3/22, 13.6%), but they were also more prone , p=0.68, Fisher's exactIn comparison with SS, the elicited discharges started more frequently with a FDS (n=78, The other ictal patterns included Elicited RSD was never observed. (13/23, 56.5%), were elicited by a Pts: patients; n°: number; clinical seizure elicited by CES; : aura: electro-clinical aura ted by CES; NHS: non habitual electro-clinical ted by CES; * 5 (in 5 pts) were part of auras, and 4 (in 4 pts) were part of CS; ** 5 (in 5 pts) were of CS; TLE: temporal lobe epilepsy; FLE:

Figure 1a .

 1a Figure 1a. Spontaneous seizure (patient 29). Low voltage fast activity (LVFA) involving first the amygdala (*), followed by a mixture of LVFA with a fast discharge of spikes within mesial temporal structures 12 seconds later (arrow). The discharge then propagate to the insula an operculum; STG: superior temporal gyrus; MesioT: mesio

Figure 2a :

 2a Figure 2a: spontaneous seizure: the discharge involves first (*) the left mesial temporal structures (mesioT), becoming more tonic and spreading (arrow) 54 s after the onset, to the left insular cortex, the left temporal neocortex (aMTG, pMTG, PSTG) and to the right mesial temporal the right insula. L: left. R/right. MesioT: mesial temporal structures. aMTG: anterior middle temporal gyrus. pMTG: posterior first temporal gyrus. Amy: amygdala. Hc: hippocampus. EKG: electrocardiogram. the discharge involves first (*) the left mesial temporal structures (mesioT), becoming more tonic and spreading (arrow) 54 s after the onset, to the left insular cortex, the left temporal neocortex (aMTG, pMTG, PSTG) and to the right mesial temporal structures (amygdala and hippocampus) and the right insula. L: left. R/right. MesioT: mesial temporal structures. aMTG: anterior middle temporal gyrus. pMTG: posterior middle temporal gyrus. pSTG : posterior ampus. EKG: electrocardiogram.

Figure 2b :

 2b Figure 2b: right amygdala 50Hz stimulation insula, as in the second part of the spontaneous seizure.

Table 1 :

 1

	focal cortical dysplasia; HS: hippocampal sclerosis; MMCDOH: mild malformation of cortical developement
	with oligodendroglial cells; PVNH: pervicentricular nodular heterotopia; RFTC: radiofrequency
	previously operated (#5: R F oligodendroglioma; #7: R F DNET; #8: L
	F cavernoma; #10: L F resection/disconnection (negative histology); #21: L F resection with negative MRI; #22:

Patient's characteristics. are highlighted in grey (n=24). Pt: patient number; M: male; F:female; N: normal; R: right; L: left; F: frontal; T: temporal; P: parietal; C:central; Ins: insular; O: occipital ; focal cortical dysplasia; HS: hippocampal sclerosis; MMCDOH: mild malformation of cortical developement with oligodendroglial cells; PVNH: pervicentricular nodular heterotopia; RFTC: radiofrequency thermocoagulation; NA: not applicable; F cavernoma; #10: L F resection/disconnection (negative histology); #21: L F resection with negative MRI; #22: L T disconnection with negative MRI).

Table 1: Patient's characteristics. Patients who experienced at least one CES-elicited electro are highlighted in grey (n=24). Pt: patient number; M: male; F:female; N: normal; R: right; L: left; F: frontal; T: temporal; P: parietal; C:central; Ins: insular; O: occipital ; DNET: dysembryoplasic neuroepithelial tumor; FCD: focal cortical dysplasia; HS: hippocampal sclerosis; MMCDOH: mild malformation of cortical developement with oligodendroglial cells; PVNH: pervicentricular nodular heterotopia; RFTC: radiofrequency agulation; NA: not applicable; 1 previously operated (#5: R F oligodendroglioma; #7: R F DNET; #8: L F cavernoma; #10: L F resection/disconnection (negative histology); #21: L F resection with negative MRI; #22: L T disconnection with negative MRI). 10 elicited electro-clinical seizure are highlighted in grey (n=24). Pt: patient number; M: male; F:female; N: normal; R: right; L: left; F: frontal; T: DNET: dysembryoplasic neuroepithelial tumor; FCD:

Table 2 :

 2

Comparison between stimulation experienced at least one complete CES patient; SS: spontaneous seizures; EZ: epileptogenic zone; CESS: electro (cortical electrical stimulation); CS: complete electro available; na: not applicable.

Table 2 :

 2 Comparison between stimulation-induced and spontaneous electro-clinical seizures.

Table 3 :

 3 General characteristics of stimulation

Remerciements à messieurs Fabrice Bartolomei, Stephan Chabardes, Olivier David et François Dubeau pour avoir accepté d'expertiser ce travail et d'en composer le jury.

Recevez toute ma gratitude.

J'exprime particulièrement ma sincère reconnaissance à Lorella Minotti et Philippe Kahane, qui m'ont encadrée chaleureusement tout au long de ce travail, et pendant mon cursus.

Remerciements

A Aurélie pour les footings du matin, et ce semestre en neuro gé transformé grâce à toi.

A Margaux, que j'admire tant et que j'aurai voulu voir plus souvent.

A Anais, pour son peps, et sa joie de vivre qui transcende les gens alentours.

A Eve pour cette année de coloc, le chocolat dans le placard et le fromage dans le frigo, que je mangeais autant que toi, les virées à carrefour à 21h et surtout ces dernières semaines où tu m'as supportée et chouchouter. A Benjamin, mon amour. Merci de m'avoir attendue pendant toutes ces années, de ne pas avoir lâché malgré la distance et les coups durs, les concours blancs, les heures dans les bouquins à la lumière de ta petite lampe de bureau, puis les gardes, le tout malgré mon stress parfois ingérable. Merci de ton honnêteté et ton intégrité qui m'ont transformée, de ta confiance en moi. Merci d'avoir traversé ma vie et d'avoir grandi avec moi. Notre histoire est déjà si belle, notre nouvelle vie qui commence risque de nous transporter, comme ce fameux train qui ne cessait d'accélérer...