Frédérique Robin

Ahmed A Moustafa

Mohamad El Haj
email: mohamad.elhaj@univ-nantes.fr

The image of memory: relationship between autobiographical

Keywords: memory and mental imagery in Korsakoff syndrome autobiographical memory, Korsakoff's syndrome, mental imagery, spatial imagery, visual imagery

published or not. The documents may come

Mental imagery 3

Korsakoff syndrome (KS) is an acute neurological syndrome caused by malnutrition, thiamine deficiency, and prolonged heavy ingestion of alcohol [START_REF] Arts | Korsakoff's syndrome: a critical review[END_REF][START_REF] Kessels | Context memory in Korsakoff's syndrome[END_REF]. At the cognitive level, KS is mainly associated with general impairment of memory [START_REF] Arts | Korsakoff's syndrome: a critical review[END_REF][START_REF] Fama | Anterograde episodic memory in Korsakoff syndrome[END_REF][START_REF] Kopelman | Remote and autobiographical memory, temporal context memory and frontal atrophy in Korsakoff and Alzheimer patients[END_REF] and, more specifically, with impairment of autobiographical memory, that is, memory for personal information (M. A. [START_REF] Conway | Memory and the self[END_REF][START_REF] Rubin | A basic-systems approach to autobiographical memory[END_REF]. The impairment of autobiographical memory in KS is the main topic of our paper. More specifically, this paper investigates the relationship between impairment of autobiographical memory in KS and the ability to generate mental images. Given this objective, we next describe current knowledge on autobiographical memory in KS, and also describe current knowledge on the relationship between autobiographical memory and mental imagery in populations other than KS since little is known about this relationship in the syndrome.

One main characteristic of autobiographical memory in KS is the difficulty of patients to retrieve specific memories, that is, to retrieve personal events that had happened at a particular place and time. This difficulty has been observed by [START_REF] Kopelman | Remote and autobiographical memory, temporal context memory and frontal atrophy in Korsakoff and Alzheimer patients[END_REF] who asked patients with KS to retrieve specific autobiographical events. The results show that patients tended to produce general rather than specific memories. Similar findings were reported by El Haj and colleagues [START_REF] El Haj | Tell about yourself to improve your autobiographical memory: A study of Korsakoff's syndrome[END_REF]El Haj & Nandrino, 2017[START_REF] Aydin | The differential contributions of visual imagery constructs on autobiographical thinking[END_REF] who invited patients with KS to retrieve autobiographical memories that were analyzed regarding specificity, that is, whether each memory depicted 1) a general theme, 2) a repeated or an extended event, 3) an event situated in time and/or space, 4) a specific event lasting less than 24 h and situated in time and space, or 5) a specific event situated in time and space enriched with phenomenological details such as feelings, perceptions or emotions.

Using this analysis, El Haj and colleagues (El Haj et al., 2018;El Haj & Nandrino, 2017[START_REF] Aydin | The differential contributions of visual imagery constructs on autobiographical thinking[END_REF] found low autobiographical specificity in patients with KS. The difficulty of patients Mental imagery 4 with KS to retrieve specific memories has been also reported by research demonstrating difficulties in patients with KS to remember the specific context in which self-unrelated information was previously encountered, such as remembering position of a spot of light presented on a board [START_REF] Holdstock | A comparison of egocentric and allocentric spatial memory in medial temporal lobe and Korsakoff amnesics[END_REF], location of pictures on cards [START_REF] Kopelman | Temporal and spatial context memory in patients with focal frontal, temporal lobe, and diencephalic lesions[END_REF], location of pictures of objects in grids [START_REF] Shoqeirat | Disproportionate incidental spatial-memory and recall deficits in amnesia[END_REF], location of words presented in the corners of a screen [START_REF] Mayes | Disproportionate intentional spatialmemory impairments in amnesia[END_REF], location in which objects had been placed [START_REF] El Haj | Source monitoring in Korsakoff's syndrome: "Did I touch the toothbrush or did I imagine doing so?[END_REF], to whom information has been told [START_REF] El Haj | Destination Memory in Korsakoff's Syndrome[END_REF], and duration of events [START_REF] Brand | Cognitive estimation in patients with probable Alzheimer's disease and alcoholic Korsakoff patients[END_REF][START_REF] Brion | Source Memory in Korsakoff Syndrome: Disentangling the Mechanisms of Temporal Confusion[END_REF][START_REF] El Haj | Retrospective Time Perception in Korsakoff's Syndrome[END_REF][START_REF] Kinsbourne | The extended present: Evidence from time estimation by amnesics and normals[END_REF][START_REF] Mimura | Time estimation by patients with frontal lesions and by Korsakoff amnesics[END_REF]. These studies mirror the general impairment of episodic memory in KS [START_REF] Fama | Dissociation of remote and anterograde memory impairment and neural correlates in alcoholic Korsakoff syndrome[END_REF][START_REF] Fama | Anterograde episodic memory in Korsakoff syndrome[END_REF][START_REF] Pitel | Episodic and working memory deficits in alcoholic Korsakoff patients: the continuity theory revisited[END_REF] as well as the contextual account according to which episodic memory decline in KS is caused by an inability to encode, store or retrieve contextual information [START_REF] Kessels | Context memory in Korsakoff's syndrome[END_REF].

The difficulty of patients with KS to retrieve specific autobiographical memories can be related to problems to generate mental images. Our assumption can be supported by studies in healthy populations demonstrating that mental imagery contributes to several phenomenological properties of autobiographical memory such as vividness (D'Argembeau & [START_REF] D'argembeau | Individual differences in the phenomenology of mental time travel: The effect of vivid visual imagery and emotion regulation strategies[END_REF][START_REF] Rubin | Belief and recollection of autobiographical memories[END_REF], realness [START_REF] Mazzoni | Imagination Can Create False Autobiographical Memories[END_REF], and critically, memory specificity [START_REF] Dewhurst | Pictures, images, and recollective experience[END_REF][START_REF] Williams | The effect of imageability and predicability of cues in autobiographical memory[END_REF]. Further, one study has reported enhanced autobiographical retrieval in healthy individuals with high mental imagery than in those with low mental imagery [START_REF] Vannucci | Visual object imagery and autobiographical memory: Object Imagers are better at remembering their personal past[END_REF]. Research using eye movement technology has suggested that the creation of mental images facilitates autobiographical recall by increasing Mental imagery 5 the ease and speed of search through the hierarchical structure of autobiographical memory (El Haj & Lenoble, 2017;[START_REF] El Haj | Eye movement during retrieval of emotional autobiographical memories[END_REF][START_REF] Lenoble | Don't stare, unless you don't want to remember: Maintaining fixation compromises autobiographical memory retrieval[END_REF]. This assumption fits with that of [START_REF] Conway | The construction of autobiographical memories in the self-memory system[END_REF] according to whom mental imagery provides rich contextual, sensorial, and/or perceptual information that enhances the access to general autobiographical knowledge, which acts as a powerful lever in the retrieval of specific memories.

The above-mentioned literature suggests an intimate relationship between autobiographical memory and the ability to generate mental images. It therefore follows that diminished ability to retrieve autobiographical memory may be associated with a diminished ability to generate mental images. Our assumption can be supported by neuropsychological studies showing autobiographical amnesia in patients with acquired imagery deficits. For instance, one study has demonstrated considerable difficulties in processing visual aspects of specific autobiographical events in a patient with occipital lobe damage (M. A. [START_REF] Conway | Disruption and loss of autobiographical memory[END_REF]. In a similar vein, several studies have demonstrated reduced ability to construct mental images during autobiographical retrieval in patients with damages of occipital lobes, probably because occipital lobes are associated with visual function (Greenberg & Rubin, 2003). One study has also reported retrograde amnesia (i.e., difficulty in retrieving memories that occurred before the onset of illness) and difficulty in recognizing common objects from memory as well as difficulty in generating and manipulating mental images in a patient with damage to the right occipital lobe and the occipito-temporal junction [START_REF] Greenberg | Visual memory loss and autobiographical amnesia: a case study[END_REF]. Besides being reported by neuropsychological research, the contribution of visual imagery to autobiographical memory has been highlighted by neuroimaging studies showing an association between autobiographical retrieval and increased activation in the posterior cortical regions, brain areas that play a major role in the ability to generate mental images [START_REF] Cabeza | Functional neuroimaging of autobiographical memory[END_REF]Svoboda, McKinnon, & Mental imagery 6 Levine, 2006). Taken together, there is a body of research reporting a relationship between the ability to retrieve autobiographical memory and the ability to generate mental images, a relationship that we will investigate in KS.

Since our aim was to assess the relationship between the ability of patients with KS to retrieve autobiographical memory and the ability to generate mental images, we distinguished between visual and spatial mental imagery. While both visual and spatial mental imagery are two components of mental imagery, visual imagery allows the visual appearance of objects to be represented (e.g. shape, color, and brightness) and spatial imagery allows the representations of objects to be rotated, their spatial characteristics to be scanned, and relationships to be determined between several objects in space [START_REF] Farah | Visual and spatial mental imagery: dissociable systems of representation[END_REF][START_REF] Kosslyn | Neural foundations of imagery[END_REF]. Considering autobiographical memory, visual imagery is likely to contribute to the vividness of retrieved memories whereas spatial imagery is likely to contribute to the ability to create and manipulate the visual characteristics of retrieved memories (e.g., the characteristics of the location in which the memory was encoded). This issue was investigated by El Haj, Gallouj, and Antoine (2019) who asked patients with Alzheimer's disease to retrieve autobiographical events and to perform a test of visual imagery and a test of spatial imagery; visual imagery was assessed with the Wider Taller task [START_REF] Kosslyn | A computational analysis of mental image generation: evidence from functional dissociations in splitbrain patients[END_REF] on which patients were invited to generate a mental image of an object presented as a word (e.g., car) and determine whether the object was taller than it was wide, whereas spatial imagery was assessed with the Clock Angles test [START_REF] Grossi | Visuospatial imagery in Alzheimer disease[END_REF] on which patients had to imagine the angle created by the hands on a clock set to a certain time and determine whether that angle was < 90 degrees. Using these relatively simple tests, El Haj et al. ( 2019) observed that autobiographical memory in patients with Alzheimer's disease was predicted by visual but not by spatial imagery. The authors suggested that visual imagery contributes to Mental imagery 7 autobiographical retrieval in patients with Alzheimer's disease by providing them with visual cues that improve the ease and speed of search through the hierarchical structure of autobiographical memory.

To summarize, in this exploratory study, we investigated the relationship between decline of autobiographical memory in KS and the ability to generate mental images; the latter ability was investigated with respect to visual and spatial mental imagery. We investigated this issue in light of research demonstrating that mental imagery significantly contributes to autobiographical memory (D'Argembeau & [START_REF] D'argembeau | Individual differences in the phenomenology of mental time travel: The effect of vivid visual imagery and emotion regulation strategies[END_REF][START_REF] Dewhurst | Pictures, images, and recollective experience[END_REF][START_REF] Mazzoni | Imagination Can Create False Autobiographical Memories[END_REF][START_REF] Rubin | Belief and recollection of autobiographical memories[END_REF]. We expected that autobiographical performance in patients with KS would be correlated with their ability to generate mental images. Our assumption was based on research demonstrating autobiographical amnesia in patients with acquired imagery deficits [START_REF] Brown | Severe retrograde amnesia[END_REF][START_REF] Conway | Disruption and loss of autobiographical memory[END_REF][START_REF] Greenberg | Visual memory loss and autobiographical amnesia: a case study[END_REF]Greenberg & Rubin, 2003;[START_REF] Ogden | Visual object agnosia, prosopagnosia, achromatopsia, loss of visual imagery, and autobiographical amnesia following recovery from cortical blindness: case M[END_REF].

Method

Participants

We recruited twenty-three patients diagnosed with KS (13 women and 10 men; M age = 58.17 years, SD = 5.39; M years of formal education = 9.61, SD = 3.21) from inpatient and day-care facilities in the region of North of France. We also recruited 25 control participants 2000) criteria for alcohol-induced persisting amnestic disorder, and demonstrating an extensive history of alcoholism, nutritional depletion, and notably, thiamine deficiency. All KS patients were in a chronic (more than one-year post-onset) and stable condition and had no confusional Wernicke psychosis at the time of testing or signs of alcohol-related dementia [START_REF] Oslin | Alcohol related dementia: proposed clinical criteria[END_REF]. Amnestic symptoms were present during the initial diagnosis, as confirmed by our memory examination, described below; this examination also served to confirm the normal memory performance in the control participants.

We tested verbal episodic memory with the task of [START_REF] Grober | Genuine memory deficits in dementia[END_REF] on which participants were invited to retain 16 words, each of which described an item (e.g., piano) that belonged to a different semantic category (e.g., musical instruments). This encoding phase was followed by a distraction phase during which participants were invited to count backwards from 374 in 20s. Afterward, participants were allocated two minutes of free recall and the score from this phase provided a measure of verbal episodic memory (16 points maximum). Lower verbal episodic memory was observed in patients with KS (M = 6.83, SD = 2.01) than in control participants (M = 10.72, SD = 1.67) [t(46) = 7.31, p < .001]. We tested working memory with the digit span task [START_REF] Baddeley | Working memory[END_REF] in which participants had to repeat a string of single digits in the same order (i.e., forward spans) or in reverse order (i.e., backward spans). Lower forward spans was observed in patients with KS (M = 5.30, SD = .97) than in control participants (M = 6.32, SD = 1.38) [t(46) = 2.93, p < .01] and lower backward spans was observed in patients with KS (M = 4.04, SD = .64) than in control participants (M = 5.00, SD = 1.04) [t(46) = 3.80, p < .001].

Procedures

Mental imagery 9

Visual and spatial mental imagery

We evaluated visual imagery with the Taller/Wider task [START_REF] Grossi | Visuospatial imagery in Alzheimer disease[END_REF] and spatial imagery with the Clock Angles task [START_REF] Kosslyn | A computational analysis of mental image generation: evidence from functional dissociations in splitbrain patients[END_REF]. Each task consisted of one mental imagery and one perceptual condition. The perceptual condition was implemented to ensure that any failure on the mental imagery trial was not due to a problem with visual perception; because of this perceptual condition, we excluded two patients with KS from the original sample size (n = 25 patients) as they performed two standard deviations below the group mean. For all participants, the Taller/Wider task was presented prior to the Clock Angles tasks, both tasks being separated by the working memory spans tasks.

Regarding the Clock Angles task, we invited participants in the control condition to look at 20 clock faces without numbers (but hands included), each of which was printed in black on a white A4 paper sheet. For each clock face, we invited participants to determine whether the angle between the hands was < 90 degrees. Afterward, participants proceeded to the mental imagery condition in which they viewed 20 digitally represented clock times, each of which was printed in black on a white A4 paper sheet. We invited participants to imagine the angle between the minute and hour hands (as represented on an analog clock) and determine whether that angle was < 90 degrees. Scores referred to the percentage of correct responses. Regarding Taller/Wider task, we replicated procedures of [START_REF] Kosslyn | A computational analysis of mental image generation: evidence from functional dissociations in splitbrain patients[END_REF] by exposing participants in the mental imagery condition to 20 objects (e.g., knife, pen, screwdriver) and each object was presented as a word printed in black on a white A4 paper sheet. We invited participants to decide whether each object was taller than it was wide. In the subsequent perceptual condition, we exposed participants to colored pictures of these words, each picture being printed on a white A4 paper sheet to allow the same judgment.

Scores referred to the percentage of correct responses.

Mental imagery 10

Autobiographical memory

We asked participants to retrieve two personal events, while being precise and specific, so events had to have lasted no more than a day and spatiotemporal details had to be provided, such as time and place at which the events had occurred; we provided some examples to illustrate what would be considered as a specific event. We also invited participants to describe their feelings and emotions during the retrieved events. Recall was limited to two minutes for each event and the duration was stated from the outset so participants could plan their time accordingly. We implemented this time limit to avoid potential redundancy and/or distractibility. We also assessed only two memories to avoid bias such as fatigability and redundancy and because patients with KS tend to demonstrate difficulties to retrieve several memories (El Haj et al., 2018). We recorded autobiographical retrieval using a smartphone, with the participants' approval, for later transcription.

Autobiographical performance was evaluated regarding specificity, in light of research suggesting lack of specificity as one of the main characteristics of autobiographical retrieval in patients with KS (El Haj et al., 2018;El Haj & Nandrino, 2017[START_REF] Aydin | The differential contributions of visual imagery constructs on autobiographical thinking[END_REF][START_REF] Kopelman | Remote and autobiographical memory, temporal context memory and frontal atrophy in Korsakoff and Alzheimer patients[END_REF]. We used a scoring system based on the Test Episodique de Mémoire du Passé [START_REF] Piolino | Autobiographical memory, autonoetic consciousness, and selfperspective in aging[END_REF]; this scoring system is based on autobiographical models (M. A. [START_REF] Conway | Memory and the self[END_REF] and classic autobiographical evaluations [START_REF] Kopelman | The autobiographical memory interview: a new assessment of autobiographical and personal semantic memory in amnesic patients[END_REF]) and adapted for normal and clinical French populations. Using this scale, and for each memory, we attributed zero if there was no memory or only general information about a theme; one point for a repeated or an extended event; two points for an event situated in time and/or space; three points for a specific event lasting less than 24 h and situated in time and space; and four points for a specific event situated in time and space and enriched with phenomenological details (e.g., feeling, thoughts, feelings). The maximum autobiographical score for each participant was eight points (four points for each of the two memories). Note that high inter-Mental imagery 11 rater agreement coefficients were obtained (Cohen's Kappa coefficient κ = .91) [START_REF] Brennan | Coefficient kappa: Some uses, misuses, and alternatives[END_REF] and cases of disagreement were subjected to joint evaluation.

Results

We compared the performance of patients with KS and control participants on visual imagery, spatial imagery and autobiographical memory. Comparisons were conducted using the Mann-Whitney test owing to abnormal distribution of data. Regarding effect sizes, we used Cohen's d [START_REF] Cohen | Statistical Power Analysis[END_REF]: 0.20 = small, 0.50 = medium, 0.80 = large; note that effect size was calculated for non-parametric tests following the recommendations of [START_REF] Rosenthal | Meta-analysis: recent developments in quantitative methods for literature reviews[END_REF] and [START_REF] Ellis | The Essential Guide to Effect Sizes: Statistical Power, Meta-Analysis, and the Interpretation of Research Results[END_REF]. To assess the relationship between visual imagery, spatial imagery, and autobiographical memory, we carried out Spearman rank correlations.

Afterward, we carried out stepwise regression analyses to determine which mental imagery dimension better predicted autobiographical memory.

Poor spatial imagery and autobiographical memory but preserved visual imagery in KS.

Scores are shown in Table 1. Analyses showed lower spatial imagery (Z = -3.81, p < .001, Cohen's d = 1.32) and autobiographical memory (Z = -5.48, p < .001, Cohen's d = 2.58) in patients with KS than in control participants. However, no significant differences were observed between patients with KS and control participants on visual imagery (Z = -1.59, p > .1, Cohen's d = .47). As for the control condition of visual imagery, no significant differences were observed between both populations (Z = -.99, p > .1, Cohen's d = .29), and the same thing was observed for the control condition of spatial imagery (Z = -.42, p > .1, Cohen's d = .12).

[INSERT TABLE 1 APPROXIMATELY HERE]

Mental imagery 12

Significant correlations between visual imagery, spatial imagery and autobiographical memory.

Spearman rank correlations showed significant correlations between visual imagery, spatial imagery and autobiographical memory in patients with KS and control participants (see Table 2). Note that no significant correlations were observed between perceptual tasks of visual and spatial imagery and autobiographical memory in either population (p > .1). To examine potential contribution of years since disease, we conducted partial correlations, controlling for this variable, analysis demonstrated significant correlations between visual imagery and autobiographical memory in patients with KS (r = .57, p < .01) and control participants (r = .55, p < .01) as well as significant correlations between spatial imagery and autobiographical memory in patients with KS (r = .52, p < .01) and control participants (r = .48, p < .05); no significant correlations were observed between perceptual tasks of visual and spatial imagery and autobiographical memory in either population (p > .1).

[INSERT TABLE 2 APPROXIMATELY HERE]

Autobiographical performances predicted by visual imagery.

We performed stepwise regression analyses to identify which mental imagery dimension better predicted autobiographical memory. The dependent variable was autobiographical memory and predictors were performance on the Wider Taller and the Clock Angles tasks. Analysis demonstrated that performance on the Wider Taller task was the main and only variable predicting autobiographical memory in patients with KS (adjusted R 2 = .24, p < .05) and control participants (adjusted R 2 = .35, p < .01).

Discussion

Mental imagery 13

The main aim of this study was to assess the relationship between autobiographical memory and visual and spatial imagery in KS. Analyses showed compromised spatial imagery and autobiographical memory but preserved visual imagery in patients with KS.

Analyses also demonstrated significant correlations between visual imagery, spatial imagery and autobiographical memory in patients with KS and control participants. Interestingly, autobiographical performance in patients with KS and control participants were predicted by visual but not by spatial imagery.

The correlations between autobiographical memory and visual and spatial imagery mirror the assumption of [START_REF] Conway | The construction of autobiographical memories in the self-memory system[END_REF] according to whom mental imagery provides rich contextual, sensorial, and/or perceptual information that enhances access to autobiographical memories. In a similar vein, several authors have proposed that autobiographical memories come to mind mainly in the form of mental images and that these images are one of the main format of autobiographical reliving [START_REF] Brewer | What is recollective memory?[END_REF][START_REF] Rubin | Belief and recollection of autobiographical memories[END_REF]. These theoretical assumptions are supported by studies in healthy populations demonstrating that mental imagery contributes to vividness (D'Argembeau & [START_REF] D'argembeau | Individual differences in the phenomenology of mental time travel: The effect of vivid visual imagery and emotion regulation strategies[END_REF][START_REF] Rubin | Belief and recollection of autobiographical memories[END_REF] and realness of autobiographical memories [START_REF] Mazzoni | Imagination Can Create False Autobiographical Memories[END_REF], and critically, to specificity of autobiographical memories [START_REF] Dewhurst | Pictures, images, and recollective experience[END_REF][START_REF] Williams | The effect of imageability and predicability of cues in autobiographical memory[END_REF]. Similarly, individuals with high mental imagery were found to retrieve more autobiographical memories than those with low mental imagery [START_REF] Vannucci | Visual object imagery and autobiographical memory: Object Imagers are better at remembering their personal past[END_REF]. This theoretical and experimental literature suggests the ability to generate visual images as a fundamental aspect of autobiographical retrieval, which may explain the significant correlations between autobiographical memory and mental imagery in our study.

Regarding the distinction between visual and spatial imagery, our analyses showed a significant relationship between autobiographical memory and visual and spatial imagery in Mental imagery 14 both patients with KS and control participants. Therefore, autobiographical retrieval in patients with KS seems to be related to the ability to represent visual appearance of the remembered information (i.e., visual imagery) and the ability to manipulate the visual characteristics of the remembered information (i.e., spatial imagery). More specifically, visual imagery is likely to contribute to the vividness the retrieved autobiographical memories in patients with KS whereas spatial imagery is likely to contribute to their ability to create and manipulate the visual characteristics of retrieved memories (e.g., the characteristics of the location in which the memory was encoded). However, although autobiographical retrieval was related to both visual and spatial imagery in our participants, this retrieval seems to be mainly dependent on visual imagery. This assumption is supported by our regression analysis demonstrating that autobiographical retrieval was predicted by visual but not by spatial imagery. It is likely that visual imagery might have contributed to autobiographical memory in our participants by providing them with powerful visual cues during memory retrieval. As mentioned above, visual imagery provides rich sensoryperceptual cues that enhance access to autobiographical memories (M. A. [START_REF] Conway | The construction of autobiographical memories in the self-memory system[END_REF]. Therefore, it is likely that visual imagery contributed to the autobiographical performance of patients with KS and control participants by providing them with more cues than that of spatial imagery. These cues could then have facilitated the retrieval of specific memory in the participants. Alternatively, the lack of significant contribution of spatial imagery to autobiographical retrieval can be attributed to the decline of spatial imagery in KS; unlike their performances on the assessment of mental imagery (i.e., the Wider Taller task), patients with KS in our study have demonstrated significant difficulties on the assessment of spatial imagery (i.e., the Clock Angle test). That said, [START_REF] Sheldon | Individual differences in visual imagery determine how event information is remembered[END_REF] have associated high spatial imagery with difficulties to retrieve specific memories. The authors asked healthy participants to answer questions related Mental imagery 15 to event, spatial, or feature details contained in videos, while simultaneously viewing stimuli that interfered with visual imagery processes. Results demonstrated that participants high in spatial imagery were less accurate at recalling details from the videos compared to those low in spatial imagery ability. The involvement of spatial imagery in autobiographical memory was also evaluated by [START_REF] Aydin | The differential contributions of visual imagery constructs on autobiographical thinking[END_REF] who assessed the contribution of object and spatial imagery to autobiographical retrieval in healthy participants. The author reported that while object imagery was associated with several phenomenological characteristics of retrieval, spatial imagery predicted the level of specificity. The author suggested that, while object imagery may be engaged in reflective autobiographical retrieval, spatial imagery is engaged during retrieval of memory details.

Our study assessed both visual and spatial imagery in the syndrome. To the very best of our knowledge, very little is known about these two components of mental imagery in KS.

In our study, patients with KS have demonstrated impairments on spatial but not on visual imagery. Therefore, basic visual imagery seems to be spared in KS, unlike spatial imagery which requires heavy executive demand. It is worth noting that patients with KS typically demonstrates difficulties on tasks requiring executive function [START_REF] Brion | Revisiting the continuum hypothesis: toward an in-depth exploration of executive functions in korsakoff syndrome[END_REF] and that these difficulties can be observed on tasks requiring typical executive functions such as inhibition, response generation, planning, and shifting [START_REF] Arts | Korsakoff's syndrome: a critical review[END_REF][START_REF] Van Oort | Executive dysfunction in Korsakoff's syndrome: Time to revise the DSM criteria for alcohol-induced persisting amnestic disorder[END_REF]. The difficulties of patients with KS, as observed on the Clock Angles test, can also be associated with their general impairment to retain spatial information. The latter difficulties has been reported by research demonstrating difficulties in patients with KS to remember visual information such as the position of a spot of light presented on a board [START_REF] Holdstock | A comparison of egocentric and allocentric spatial memory in medial temporal lobe and Korsakoff amnesics[END_REF], location of pictures on cards [START_REF] Kopelman | Temporal and spatial context memory in patients with focal frontal, temporal lobe, and diencephalic lesions[END_REF], location of pictures of objects in grids [START_REF] Shoqeirat | Disproportionate incidental spatial-memory and recall deficits in amnesia[END_REF], location in which objects had been placed [START_REF] El Haj | Source monitoring in Korsakoff's syndrome: "Did I touch the toothbrush or did I imagine doing so?[END_REF], or location of words Mental imagery 16 presented in the corners of a screen [START_REF] Mayes | Disproportionate intentional spatialmemory impairments in amnesia[END_REF]. The difficulties of processing spatial information in patients with KS have been also reported for autobiographical memory. This issue was investigated by El Haj and Nandrino (2017) who asked patients with KS to retrieve autobiographical memories and, after memory retrieval, patients were invited to rate phenomenological characteristics of their memories (i.e., reliving, back in time, remembering, realness, visual imagery, auditory imagery, language, emotion, rehearsal, importance, spatial recall and temporal recall). Spatial recall was evaluated with the following item "I can recall the place where the event occurred", and patients with KS reported low scores on this item. Together, KS seems to demonstrate difficulties on test of spatial imagery (i.e., the Clock Angle test) as well as difficulties to remember spatial information and, critically, difficulties to construct spatial representations of the retrieved autobiographical events.

While we tend to attribute impaired spatial imagery in patients with KS to executive dysfunction, this assumption must be interpreted with some caution because we did not assess executive function in our participants. Future research should therefore assess the relationship between performances on spatial imagery tasks and executive performance in patients with KS. Another suggestion for future research would be to test the relationship between mental imagery and confabulations, that is, the production of memories that are unintentionally incongruous with respect to the subject's history, background, and present situation [START_REF] Kopelman | Two types of confabulation[END_REF]. While, as demonstrated in our paper, autobiographical retrieval in KS is characterized by the difficulties of patients to retrieve specific memories, another characteristic of autobiographical retrieval in KS is confabulations [START_REF] Borsutzky | Confabulations in alcoholic Korsakoff patients[END_REF][START_REF] Kessels | Confabulation behavior and false memories in Korsakoff's syndrome: role of source memory and executive functioning[END_REF][START_REF] Rensen | Intrusions and provoked and spontaneous confabulations on memory tests in Korsakoff's syndrome[END_REF]. It would be of interest to test whether confabulations are Mental imagery 17 characterized by high mental imagery, which may explain why patients with KS tend to confound them with real memories.

To summarize, this study highlights the relationship between autobiographical memory and mental imagery in KS. Critically, we highlight how autobiographical retrieval in KS may depend on the ability to process visual appearance of a mental scene to be retrieved (i.e., visual imagery), and the ability to create and manipulate the visual characteristics of retrieved memories (i.e., spatial imagery). By doing so, we open a window into both cognitive and subjective characteristics of autobiographical retrieval in KS.

Table 1. Note. score of visual and mental imagery refers to percentage of correct responses; the maximum score of autobiographical performance was eight points (two memories x four points); differences between groups were significant at *** p < .001; n/s differences between groups were non-significant; comparisons were established with Mann-Whitney's U test (abnormal distribution).

Performance of patients with

Mental imagery 26

  without current or previous substance addiction and without neurological or psychiatric history (15 women and 10 men; M age = 56.04, years, SD = 5.36; M years of formal education = 9.40, SD = 4.93, M years since diagnosis = 3.25, SD = 2.54). We matched the control participants with the KS patients according to sex ratio [χ 2 (1, N = 48) = .06, p > .10], age [t(46) = 1.37, p > .10], and educational level [t(46) = .20, p > .10]. The KS patients Mental imagery 8 underwent a full examination by experienced neuropsychologists and psychiatrists, using the DSM-IV-TR (

  Korsakoff syndrome and control participants on visual (Taller/Wider task) and spatial imagery (Clock Angles task) .93, SD = 6.81 n/s M = 92.36, SD = 5.31 M = 94.96, SD = 3.72 n/s M = 96.04, SD = 2.82 Spatial imagery Perceptual (control) condition M = 72.57, SD = 7.77*** M = 81.52, SD = 5.03 M = 95.43, SD = 2.90 n/s M = 95.56, SD = 2.42 Autobiographical memory M = 5.11, SD = 1.05*** M = 7.40, SD =.82

Table 2 .

 2 Correlations between visual imagery, spatial imagery, and autobiographical memory inpatients with Korsakoff syndrome and control participants.

	1.	2.	3.


published or not. The documents may come

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