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Coast

A coast – also called the coastline, shoreline, or seashore – is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape, as well as by water induced erosion, such as waves. The geological composition of rock and soil dictates the type of shore that is created. Earth contains roughly 620,000 km of coastline.

Coasts are important zones in natural ecosystems, often home to a wide range of biodiversity. On land, they harbor important ecosystems such as freshwater or estuarine wetlands, which are important for bird populations and other terrestrial animals. In wave-protected areas, they harbor salt marshes, mangroves or seagrasses, all of which can provide nursery habitat for finfish, shellfish, and other aquatic animals. Rocky shores are usually found along exposed coasts and provide habitat for a wide range of sessile animals (e.g. mussels, starfish, barnacles) and various kinds of seaweeds.

In physical oceanography, a shore is the wider fringe that is geologically modified by the action of the body of water past and present, while the beach is at the edge of the shore, representing the intertidal zone where there is one. Along tropical coasts with clear, nutrient-poor water, coral reefs can often be found between depths of 1–50 m.

According to an atlas prepared by the United Nations, about 44% of the human population lives within 150 km of the sea. Due to its importance in society and its high population concentrations, the coast is important for major parts of the global food and economic system, and they provide many ecosystem services to humankind. For example, important human activities happen in port cities. Coastal fisheries (commercial, recreational, and subsistence) and aquaculture are major economic activities and create jobs, livelihoods, and protein for the majority of coastal human populations. Other coastal spaces like beaches and seaside resorts generate large revenues through tourism.

Marine coastal ecosystems can also provide protection against sea level rise and tsunamis. In many countries, mangroves are the primary source of wood for fuel (e.g. charcoal) and building material. Coastal ecosystems like mangroves and seagrasses have a much higher capacity for carbon sequestration than many terrestrial ecosystems, and as such can play a critical role in the near-future to help mitigate climate change effects by uptake of atmospheric anthropogenic carbon dioxide.

However, the economic importance of coasts makes many of these communities vulnerable to climate change, which causes increases in extreme weather and sea level rise, as well as related issues like coastal erosion, saltwater intrusion, and coastal flooding. Other coastal issues, such as marine pollution, marine debris, coastal development, and marine ecosystem destruction, further complicate the human uses of the coast and threaten coastal ecosystems.

The interactive effects of climate change, habitat destruction, overfishing, and water pollution (especially eutrophication) have led to the demise of coastal ecosystem around the globe. This has resulted in population collapse of fisheries stocks, loss of biodiversity, increased invasion of alien species, and loss of healthy habitats. International attention to these issues has been captured in Sustainable Development Goal 14 "Life Below Water", which sets goals for international policy focused on preserving marine coastal ecosystems and supporting more sustainable economic practices for coastal communities. Likewise, the United Nations has declared 2021-2030 the UN Decade on Ecosystem Restoration, but restoration of coastal ecosystems has received insufficient attention.

Since coasts are constantly changing, a coastline's exact perimeter cannot be determined; this measurement challenge is called the coastline paradox. The term coastal zone is used to refer to a region where interactions of sea and land processes occur. Both the terms coast and coastal are often used to describe a geographic location or region located on a coastline (e.g., New Zealand's West Coast, or the East, West, and Gulf Coast of the United States.) Coasts with a narrow continental shelf that are close to the open ocean are called pelagic coast, while other coasts are more sheltered coast in a gulf or bay. A shore, on the other hand, may refer to parts of land adjoining any large body of water, including oceans (sea shore) and lakes (lake shore).

Size
The Earth has approximately 620000 km of coastline. Coastal habitats, which extend to the margins of the continental shelves, make up about 7 percent of the Earth's oceans, but at least 85% of commercially harvested fish depend on coastal environments during at least part of their life cycle. about 2.86% of exclusive economic zones were part of marine protected areas.

The definition of coasts varies. Marine scientists think of the "wet" (aquatic or intertidal) vegetated habitats as being coastal ecosystems (including seagrass, salt marsh etc.) whilst some terrestrial scientists might only think of coastal ecosystems as purely terrestrial plants that live close to the seashore (see also estuaries and coastal ecosystems).

While there is general agreement in the scientific community regarding the definition of coast, in the political sphere, the delineation of the extents of a coast differ according to jurisdiction. Government authorities in various countries may define coast differently for economic and social policy reasons.

Formation
Tides often determine the range over which sediment is deposited or eroded. Areas with high tidal ranges allow waves to reach farther up the shore, and areas with lower tidal ranges produce deposition at a smaller elevation interval. The tidal range is influenced by the size and shape of the coastline. Tides do not typically cause erosion by themselves; however, tidal bores can erode as the waves surge up the river estuaries from the ocean.

Geologists classify coasts on the basis of tidal range into macrotidal coasts with a tidal range greater than 4 m; mesotidal coasts with a tidal range of 2 to 4 m; and microtidal coasts with a tidal range of less than 2 m. The distinction between macrotidal and mesotidal coasts is more important. Macrotidal coasts lack barrier islands and lagoons, and are characterized by funnel-shaped estuaries containing sand ridges aligned with tidal currents. Wave action is much more important for determining bedforms of sediments deposited along mesotidal and microtidal coasts than in macrotidal coasts.

Waves erode coastline as they break on shore releasing their energy; the larger the wave the more energy it releases and the more sediment it moves. Coastlines with longer shores have more room for the waves to disperse their energy, while coasts with cliffs and short shore faces give little room for the wave energy to be dispersed. In these areas, the wave energy breaking against the cliffs is higher, and air and water are compressed into cracks in the rock, forcing the rock apart, breaking it down. Sediment deposited by waves comes from eroded cliff faces and is moved along the coastline by the waves. This forms an abrasion or cliffed coast.

Sediment deposited by rivers is the dominant influence on the amount of sediment located in the case of coastlines that have estuaries. Today, riverine deposition at the coast is often blocked by dams and other human regulatory devices, which remove the sediment from the stream by causing it to be deposited inland. Coral reefs are a provider of sediment for coastlines of tropical islands.

Like the ocean which shapes them, coasts are a dynamic environment with constant change. The Earth's natural processes, particularly sea level rises, waves and various weather phenomena, have resulted in the erosion, accretion and reshaping of coasts as well as flooding and creation of continental shelves and drowned river valleys (rias).

Human settlements
More and more of the world's people live in coastal regions. According to a United Nations atlas, 44% of all people live within 150 km (93 mi) of the sea. Many major cities are on or near good harbors and have port facilities. Some landlocked places have achieved port status by building canals.

Nations defend their coasts against military invaders, smugglers and illegal migrants. Fixed coastal defenses have long been erected in many nations, and coastal countries typically have a navy and some form of coast guard.

Tourism
Coasts, especially those with beaches and warm water, attract tourists often leading to the development of seaside resort communities. In many island nations such as those of the Mediterranean, South Pacific Ocean and Caribbean, tourism is central to the economy. Coasts offer recreational activities such as swimming, fishing, surfing, boating, and sunbathing.

Growth management and coastal management can be a challenge for coastal local authorities who often struggle to provide the infrastructure required by new residents, and poor management practices of construction often leave these communities and infrastructure vulnerable to processes like coastal erosion and sea level rise. In many of these communities, management practices such as beach nourishment or when the coastal infrastructure is no longer financially sustainable, managed retreat to remove communities from the coast.

Emergent coastline
According to one principle of classification, an emergent coastline is a coastline that has experienced a fall in sea level, because of either a global sea-level change, or local uplift. Emergent coastlines are identifiable by the coastal landforms, which are above the high tide mark, such as raised beaches. In contrast, a submergent coastline is one where the sea level has risen, due to a global sea-level change, local subsidence, or isostatic rebound. Submergent coastlines are identifiable by their submerged, or "drowned" landforms, such as rias (drowned valleys) and fjords

Concordant coastline
According to the second principle of classification, a concordant coastline is a coastline where bands of different rock types run parallel to the shore. These rock types are usually of varying resistance, so the coastline forms distinctive landforms, such as coves. Discordant coastlines feature distinctive landforms because the rocks are eroded by the ocean waves. The less resistant rocks erode faster, creating inlets or bay; the more resistant rocks erode more slowly, remaining as headlands or outcroppings.

High and low energy coasts
Parts of a coastline can be categorised as high energy coast or low energy coast. The distinguishing characteristics of a high energy coast are that the average wave energy is relatively high so that erosion of small grained material tends to exceed deposition, and consequently landforms like cliffs, headlands and wave-cut terraces develop. Low energy coasts are generally sheltered from waves, or in regions where the average wind wave and swell conditions are relatively mild. Low energy coasts typically change slowly, and tend to be depositional environments.

High energy coasts are exposed to the direct impact of waves and storms, and are generally erosional environments. High energy storm events can make large changes to a coastline, and can move significant amounts of sediment over a short period, sometimes changing a shoreline configuration.

Destructive and constructive waves
Swash is the shoreward flow after the break, backwash is the water flow back down the beach. The relative strength of flow in the swash and backwash determines what size grains are deposited or eroded. This is dependent on how the wave breaks and the slope of the shore. Depending on the form of the breaking wave, its energy can carry granular material up the beach and deposit it, or erode it by carrying more material down the slope than up it. Steep waves that are close together and break with the surf plunging down onto the shore slope expend much of their energy lifting the sediment. The weak swash does not carry it far up the slope, and the strong backwash carries it further down the slope, where it either settles in deeper water or is carried along the shore by a longshore current induced by an angled approach of the wave-front to the shore. These waves which erode the beach are called destructive waves. Low waves that are further apart and break by spilling, expend more of their energy in the swash which carries particles up the beach, leaving less energy for the backwash to transport them downslope, with a net constrictive influence on the beach.

Rivieras
Riviera is an Italian word for "shoreline", ultimately derived from Latin ripa ("riverbank"). It came to be applied as a proper name to the coast of the Ligurian Sea, in the form riviera ligure, then shortened to riviera. Historically, the Ligurian Riviera extended from Capo Corvo (Punta Bianca) south of Genoa, north and west into what is now French territory past Monaco and sometimes as far as Marseilles. Today, this coast is divided into the Italian Riviera and the French Riviera, although the French use the term "Riviera" to refer to the Italian Riviera and call the French portion the "Côte d'Azur".

As a result of the fame of the Ligurian rivieras, the term came into English to refer to any shoreline, especially one that is sunny, topographically diverse and popular with tourists. Such places using the term include the Australian Riviera in Queensland and the Turkish Riviera along the Aegean Sea.

Other coastal categories

 * A cliffed coast or abrasion coast is one where marine action has produced steep declivities known as cliffs.
 * A flat coast is one where the land gradually descends into the sea.
 * A graded shoreline is one where wind and water action has produced a flat and straight coastline.
 * A primary coast isone which is mainly undergoing early stage development by major long-term processes such as tectonism and climate change A secondary coast is one where the primary processes have mostly stabilised, and more localised processes have become prominent.
 * An erosional coast is on average undergoing erosion, while a depositional coast is accumulating material.
 * An active coast is on the edge of a tectonic plate, while a passive coast is usually on a substantial continental shelf or away from a plate edge.

Landforms
The following articles describe some coastal landforms:

 * Barrier island
 * Bay
 * Headland
 * Cove
 * Peninsula

Cliff erosion

 * Much of the sediment deposited along a coast is the result of erosion of a surrounding cliff, or bluff. Sea cliffs retreat landward because of the constant undercutting of slopes by waves. If the slope/cliff being undercut is made of unconsolidated sediment it will erode at a much faster rate than a cliff made of bedrock.
 * A natural arch is formed when a headland is eroded through by waves.
 * Sea caves are made when certain rock beds are more susceptible to erosion than the surrounding rock beds because of different areas of weakness. These areas are eroded at a faster pace creating a hole or crevice that, through time, by means of wave action and erosion, becomes a cave.
 * A stack is formed when a headland is eroded away by wave and wind action or an arch collapses leaving an offshore remnant.
 * A stump is a shortened sea stack that has been eroded away or fallen because of instability.
 * Wave-cut notches are caused by the undercutting of overhanging slopes which leads to increased stress on cliff material and a greater probability that the slope material will fall. The fallen debris accumulates at the bottom of the cliff and is eventually removed by waves.
 * A wave-cut platform forms after erosion and retreat of a sea cliff has been occurring for a long time. Gently sloping wave-cut platforms develop early on in the first stages of cliff retreat. Later, the length of the platform decreases because the waves lose their energy as they break further offshore.

Coastal features formed by sediment

 * Beach
 * Beach cusps
 * Cuspate foreland
 * Dune system
 * Mudflat
 * Raised beach
 * Ria
 * Shoal
 * Spit
 * Strand plain
 * Surge channel
 * Tombolo

Coastal features formed by another feature

 * Estuary
 * Lagoon
 * Salt marsh
 * Mangrove forests
 * Kelp forests
 * Coral reefs
 * Oyster reefs

Other features on the coast

 * Concordant coastline
 * Discordant coastline
 * Fjord
 * Island
 * Island arc
 * Machair

Coastal waters
"Coastal waters" (or "coastal seas") is a rather general term used differently in different contexts, ranging geographically from the waters within a few kilometers of the coast, through to the entire continental shelf which may stretch for more than a hundred kilometers from land. Thus the term coastal waters is used in a slightly different way in discussions of legal and economic boundaries (see territorial waters and international waters) or when considering the geography of coastal landforms or the ecological systems operating through the continental shelf (marine coastal ecosystems). The research on coastal waters often divides into these separate areas too.

The dynamic fluid nature of the ocean means that all components of the whole ocean system are ultimately connected, although certain regional classifications are useful and relevant. The waters of the continental shelves represent such a region. The term "coastal waters" has been used in a wide variety of different ways in different contexts. In European Union environmental management it extends from the coast to just a few nautical miles while in the United States the US EPA considers this region to extend much further offshore.

"Coastal waters" has specific meanings in the context of commercial coastal shipping, and somewhat different meanings in the context of naval littoral warfare. Oceanographers and marine biologists have yet other takes. Coastal waters have a wide range of marine habitats from enclosed estuaries to the open waters of the continental shelf.

Similarly, the term littoral zone has no single definition. It is the part of a sea, lake, or river that is close to the shore. In coastal environments, the littoral zone extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged.

Coastal waters can be threatened by coastal eutrophication and harmful algal blooms.

In geology
The identification of bodies of rock formed from sediments deposited in shoreline and nearshore environments (shoreline and nearshore facies) is extremely important to geologists. These provide vital clues for reconstructing the geography of ancient continents (paleogeography). The locations of these beds show the extent of ancient seas at particular points in geological time, and provide clues to the magnitudes of tides in the distant past.

Sediments deposited in the shoreface are preserved as lenses of sandstone in which the upper part of the sandstone is coarser than the lower part (a coarsening upwards sequence). Geologists refer to these are parasequences. Each records an episode of retreat of the ocean from the shoreline over a period of 10,000 to 1,000,000 years. These often show laminations reflecting various kinds of tidal cycles.

Some of the best-studied shoreline deposits in the world are found along the former western shore of the Western Interior Seaway, a shallow sea that flooded central North America during the late Cretaceous Period (about 100 to 66 million years ago). These are beautifully exposed along the Book Cliffs of Utah and Colorado.

Geologic processes
The following articles describe the various geologic processes that affect a coastal zone:

 * Attrition
 * Currents
 * Denudation
 * Deposition
 * Erosion
 * Flooding
 * Longshore drift
 * Marine sediments
 * Saltation
 * Sea level change
 * eustatic
 * isostatic
 * Sedimentation
 * Coastal sediment supply
 * sediment transport
 * solution
 * subaerial processes
 * suspension
 * Tides
 * Water waves
 * diffraction
 * refraction
 * wave breaking
 * wave shoaling
 * Weathering

Animals
Larger animals that live in coastal areas include puffins, sea turtles and rockhopper penguins, among many others. Sea snails and various kinds of barnacles live on rocky coasts and scavenge on food deposited by the sea. Some coastal animals are used to humans in developed areas, such as dolphins and seagulls who eat food thrown for them by tourists. Since the coastal areas are all part of the littoral zone, there is a profusion of marine life found just off-coast, including sessile animals such as corals, sponges, starfish, mussels, seaweeds, fishes, and sea anemones.

There are many kinds of seabirds on various coasts. These include pelicans and cormorants, who join up with terns and oystercatchers to forage for fish and shellfish. There are sea lions on the coast of Wales and other countries.

Plants
Many coastal areas are famous for their kelp beds. Kelp is a fast-growing seaweed that can grow up to half a meter a day in ideal conditions. Mangroves, seagrasses, macroalgal beds, and salt marsh are important coastal vegetation types in tropical and temperate environments respectively. Restinga is another type of coastal vegetation.

Threats
Coasts also face many human-induced environmental impacts and coastal development hazards. The most important ones are:
 * Pollution which can be in the form of water pollution, nutrient pollution (leading to coastal eutrophication and harmful algal blooms), oil spills or marine debris that is contaminating coasts with plastic and other trash.
 * Sea level rise, and associated issues like coastal erosion and saltwater intrusion.

Pollution
The pollution of coastlines is connected to marine pollution which can occur from a number of sources: Marine debris (garbage and industrial debris); the transportation of petroleum in tankers, increasing the probability of large oil spills; small oil spills created by large and small vessels, which flush bilge water into the ocean.

Global goals
International attention to address the threats of coasts has been captured in Sustainable Development Goal 14 "Life Below Water" which sets goals for international policy focused on preserving marine coastal ecosystems and supporting more sustainable economic practices for coastal communities. Likewise, the United Nations has declared 2021–2030 the UN Decade on Ecosystem Restoration, but restoration of coastal ecosystems has received insufficient attention.

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Catatonia

Catatonia is a complex neuropsychiatric behavioral syndrome that is characterized by abnormal movements, immobility, abnormal behaviors, and withdrawal. The onset of catatonia can be acute or subtle and symptoms can wax, wane, or change during episodes. It has historically been related to schizophrenia (catatonic schizophrenia), but catatonia is most often seen in mood disorders. It is now known that catatonic symptoms are nonspecific and may be observed in other mental, neurological, and medical conditions. Catatonia is now a stand-alone diagnosis (although some experts disagree), and the term is used to describe a feature of the underlying disorder.

There are several subtypes of catatonia: akinetic catatonia, excited catatonia, malignant catatonia, and delirious mania.

Failure to recognize and treat catatonia may lead to poor outcomes and can be potentially fatal. Treatment with benzodiazepines or ECT can lead to remission of catatonia. There is growing evidence of the effectiveness of the NMDA receptor antagonists amantadine and memantine for benzodiazepine-resistant catatonia. Antipsychotics are sometimes employed, but they can worsen symptoms and have serious adverse effects.

Signs and symptoms
The presenting signs of catatonia vary greatly and may be subtle or more markedly pronounced, and symptoms may develop over hours or days to weeks.

Because most patients with catatonia have an underlying psychiatric illness, the majority will present with worsening depression, mania, or psychosis followed by catatonia symptoms. Catatonia presents as a motor disturbance in which patients will display marked reduction in movement, marked agitation, or a mixture of both despite having the physical capacity to move normally. These patients may be unable to start an action or stop one. Movements and mannerisms may be repetitive, or purposeless.

The most common signs of catatonia are immobility, mutism, withdrawal and refusal to eat, staring, negativism, posturing (rigidity), rigidity, waxy flexibility/catalepsy, stereotypy (purposeless, repetitive movements), echolalia or echopraxia, verbigeration (repeat meaningless phrases). It should not be assumed that patients presenting with catatonia are unaware of their surroundings as some patients can recall in detail their catatonic state and their actions.

There are several subtypes of catatonia and they are characterized by the specific movement disturbance and associated features. Although catatonia can be divided into various subtypes, the natural history of catatonia is often fluctuant and different states can exist within the same individual.

Subtypes
Withdrawn Catatonia: This form of catatonia is characterized by decreased response to external stimuli, immobility or inhibited movement, mutism, staring, posturing, and negativism. Patients may sit or stand in the same position for hours, may hold odd positions, and may resist movement of their extremities.

Excited Catatonia: Excited catatonia is characterized by odd mannerisms/gestures, performing purposeless or inappropriate actions, excessive motor activity, restlessness, stereotypy, impulsivity, agitation, and combativeness. Speech and actions may be repetitive or mimic another person's. People in this state are extremely hyperactive and may have delusions and hallucinations.

Malignant Catatonia: Malignant catatonia is a life-threatening condition that may progress rapidly within a few days. It is characterized by fever, abnormalities in blood pressure, heart rate, respiratory rate, diaphoresis (sweating), and delirium. Certain lab findings are common with this presentation; however, they are nonspecific, which means that they are also present in other conditions and do not diagnose catatonia. These lab findings include: leukocytosis, elevated creatine kinase, low serum iron. The signs and symptoms of malignant catatonia overlap significantly with neuroleptic malignant syndrome (NMS) and so a careful history, review of medications, and physical exam are critical to properly differentiate these conditions. For example, if the patient has waxy flexibility and holds a position against gravity when passively moved into that position, then it is likely catatonia. If the patient has a "lead-pipe rigidity" then NMS should be the prime suspect.

Other forms:
 * Periodic catatonia is an inconsistently defined entity. In the Wernicke-Kleist-Leonhard school, it is a distinct form of "non-system schizophrenia" characterized by recurrent acute phases with hyperkinetic and akinetic features and often psychotic symptoms, and the build-up of a residual state in between these acute phases, which is characterized by low-level catatonic features and aboulia of varying severity. The condition has a strong hereditary component. According to modern classifications, this may be diagnosed as a form of bipolar disorder, schizoaffective disorder or schizophrenia. Independently, the term periodic catatonia is sometimes used in modern literature to describe a syndrome of recurrent phases of acute catatonia (excited or inhibited type) with full remission between episodes, which resembles the description of "motility psychosis" in the Wernicke-Kleist-Leonhard school.
 * System catatonias or systematic catatonias are only defined in the Wernicke-Kleist-Leonhard school. These are chronic-progressive conditions characterized by specific disturbances of volition and psychomotricity, leading to a dramatic decline of executive and adaptive functioning and ability to communicate. They are considered forms of schizophrenia but distinct from other schizophrenic conditions. Affective flattening and apparent loss of interests are common but may be related to reduced emotional expression rather than lack of emotion. Heredity is low. Of the 21 different forms (6 "simple" and 15 "combined" forms) that have been described, most overlap only partially - if at all - with current definitions of either catatonia or schizophrenia, and thus are difficult to classify according to modern diagnostic manuals.
 * Early childhood catatonias are also a diagnosis exclusive to the Wernicke-Kleist-Leonhard school, and refers to system catatonias that manifest in young children. Clinically, these conditions resemble severe regressive forms of autism.
 * Chronic catatonia-like breakdown or autistic catatonia refers to a functional decline seen in some patients with pre-existing autism spectrum disorder and/or intellectual disability which usually runs a chronic-progressive course and encompasses attenuated catatonic symptoms as well as mood and anxiety symptoms that increasingly interfere with adaptive functioning. Onset is typically insidious and often mistaken for background autistic symptoms. Slowing of voluntary movement, reduced speech, aboulia, increased prompt dependency and obsessive-compulsive symptoms are frequently seen; negativism, (auto-)aggressive behaviors and ill-defined hallucinations have also been reported. Both the causes of this disorder as well as its prognosis appear to be heterogenous, with most patients showing partial recovery upon treatment. It seems to be related to chronic stress as a result of life transitions, loss of external time structuring, sensory sensitivities and/or traumatic experiences, co-morbid mental disorders, or other unknown causes. Since clinical catatonia can not always be diagnosed, this condition has also been renamed to the more general term "late regression".

Complications
Patients may experience several complications from being in a catatonic state. The nature of these complications will depend on the type of catatonia being experienced by the patient. For example, patients presenting with withdrawn catatonia may have refusal to eat which will in turn lead to malnutrition and dehydration. Furthermore, if immobility is a symptom the patient is presenting with, then they may develop pressure ulcers, muscle contractions, and are at risk of developing deep vein thrombosis (DVT) and pulmonary embolus (PE). Patients with excited catatonia may be aggressive and violent, and physical trauma may result from this. Catatonia may progress to the malignant type which will present with autonomic instability and may be life-threatening. Other complications also include the development of pneumonia and neuroleptic malignant syndrome.

Causes
Catatonia is almost always secondary to another underlying illness, often a psychiatric disorder. Mood disorders such as a bipolar disorder and depression are the most common etiologies to progress to catatonia. Other psychiatric associations include schizophrenia and other primary psychotic disorders. It also is related to autism spectrum disorders and ADHD. Psychodynamic theorists have interpreted catatonia as a defense against the potentially destructive consequences of responsibility, and the passivity of the disorder provides relief.

Catatonia is also seen in many medical disorders, including infections (such as encephalitis), autoimmune disorders, meningitis, focal neurological lesions (including strokes), alcohol withdrawal, abrupt or overly rapid benzodiazepine withdrawal,  cerebrovascular disease, neoplasms, head injury, and some metabolic conditions (homocystinuria, diabetic ketoacidosis, hepatic encephalopathy, and hypercalcaemia).

Pathogenesis
The pathophysiology that leads to catatonia is still poorly understood and a definite mechanism remains unknown. Neurologic studies have implicated several pathways; however, it remains unclear whether these findings are the cause or the consequence of the disorder.

Abnormalities in GABA, glutamate signaling, serotonin, and dopamine transmission are believed to be implicated in catatonia.

Furthermore, it has also been hypothesized that pathways that connect the basal ganglia with the cortex and thalamus is involved in the development of catatonia.

Diagnosis
There is not yet a definitive consensus regarding diagnostic criteria of catatonia. In the fifth edition of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-5, 2013) and the World Health Organization's eleventh edition of the International Classification of Diseases (ICD-11, 2022), the classification is more homogeneous than in earlier editions. Prominent researchers in the field have other suggestions for diagnostic criteria.

DSM-5 classification

The DSM-5 does not classify catatonia as an independent disorder, but rather it classifies it as catatonia associated with another mental disorder, due to another medical condition, or as unspecified catatonia.

Catatonia is diagnosed by the presence of three or more of the following 12 psychomotor symptoms in association with a mental disorder, medical condition, or unspecified:
 * stupor: no psycho-motor activity; not actively relating to the environment
 * catalepsy: passive induction of a posture held against gravity
 * waxy flexibility: allowing positioning by an examiner and maintaining that position
 * mutism: no, or very little, verbal response (exclude if known aphasia)
 * negativism: opposition or no response to instructions or external stimuli
 * posturing: spontaneous and active maintenance of a posture against gravity
 * mannerisms that are odd, circumstantial caricatures of normal actions
 * stereotypy: repetitive, abnormally frequent, non-goal-directed movements
 * agitation, not influenced by external stimuli
 * grimacing: keeping a fixed facial expression
 * echolalia: mimicking another's speech
 * echopraxia: mimicking another's movements.

Other disorders (additional code 293.89 [F06.1] to indicate the presence of the co-morbid catatonia):
 * Catatonia associated with autism spectrum disorder
 * Catatonia associated with schizophrenia spectrum and other psychotic disorders
 * Catatonia associated with brief psychotic disorder
 * Catatonia associated with schizophreniform disorder
 * Catatonia associated with schizoaffective disorder
 * Catatonia associated with a substance-induced psychotic disorder
 * Catatonia associated with bipolar and related disorders
 * Catatonia associated with major depressive disorder
 * Catatonic disorder due to another medical condition

If catatonic symptoms are present but do not form the catatonic syndrome, a medication- or substance-induced aetiology should first be considered.

ICD-11 classification

In ICD-11 catatonia is defined as a syndrome of primarily psychomotor disturbances that is characterized by the simultaneous occurrence of several symptoms such as stupor; catalepsy; waxy flexibility; mutism; negativism; posturing; mannerisms; stereotypies; psychomotor agitation; grimacing; echolalia and echopraxia. Catatonia may occur in the context of specific mental disorders, including mood disorders, schizophrenia or other primary psychotic disorders, and Neurodevelopmental disorders, and may be induced by psychoactive substances, including medications. Catatonia may also be caused by a medical condition not classified under mental, behavioral, or neurodevelopmental disorders.

Assessment/Physical
Catatonia is often overlooked and under-diagnosed. Patients with catatonia most commonly have an underlying psychiatric disorder, for this reason, physicians may overlook signs of catatonia due to the severity of the psychosis the patient is presenting with. Furthermore, the patient may not be presenting with the common signs of catatonia such as mutism and posturing. Additionally, the motor abnormalities seen in catatonia are also present in psychiatric disorders. For example, a patient with mania will show increased motor activity that may progress to exciting catatonia. One way in which physicians can differentiate between the two is to observe the motor abnormality. Patients with mania present with increased goal-directed activity. On the other hand, the increased activity in catatonia is not goal-directed and often repetitive.

Catatonia is a clinical diagnosis and there is no specific laboratory test to diagnose it. However, certain testing can help determine what is causing the catatonia. An EEG will likely show diffuse slowing. If seizure activity is driving the syndrome, then an EEG would also be helpful in detecting this. CT or MRI will not show catatonia; however, they might reveal abnormalities that might be leading to the syndrome. Metabolic screens, inflammatory markers, or autoantibodies may reveal reversible medical causes of catatonia.

Vital signs should be frequently monitored as catatonia can progress to malignant catatonia which is life-threatening. Malignant catatonia is characterized by fever, hypertension, tachycardia, and tachypnea.

Rating scale
Various rating scales for catatonia have been developed, however, their utility for clinical care has not been well established. The most commonly used scale is the Bush-Francis Catatonia Rating Scale (BFCRS) (external link is provided below). The scale is composed of 23 items with the first 14 items being used as the screening tool. If 2 of the 14 are positive, this prompts for further evaluation and completion of the remaining 9 items.

A diagnosis can be supported by the lorazepam challenge or the zolpidem challenge. While proven useful in the past, barbiturates are no longer commonly used in psychiatry; thus the option of either benzodiazepines or ECT.

Differential diagnosis
The differential diagnosis of catatonia is extensive as signs and symptoms of catatonia may overlap significantly with those of other conditions. Therefore, a careful and detailed history, medication review, and physical exam are key to diagnosing catatonia and differentiating it from other conditions. Furthermore, some of these conditions can themselves lead to catatonia. The differential diagnosis is as follows:
 * Neuroleptic malignant syndrome (NMS) and catatonia are both life-threatening conditions that share many of the same characteristics including fever, autonomic instability, rigidity, and delirium. Lab values of low serum iron, elevated creatine kinase, and white blood cell count are also shared by the two disorders further complicating the diagnosis. There are features of malignant catatonia (posturing, impulsivity, etc.) that are absent from NMS and the lab results are not as consistent in malignant catatonia as they are in NMS. Some experts consider NMS to be a drug-induced condition associated with antipsychotics, particularly, first generation antipsychotics, but it has not been established as a subtype. Therefore, discontinuing antipsychotics and starting benzodiazepines is a treatment for this condition, and similarly it is helpful in catatonia as well.
 * Anti-NMDA receptor encephalitis is an autoimmune disorder characterized by neuropsychiatric features and the presence of IgG antibodies. The presentation of anti-NMDAR encephalitis has been categorized into 5 phases: prodromal phase, psychotic phase, unresponsive phase, hyperkinetic phase, and recovery phase. The psychotic phase progresses into the unresponsive phase characterized by mutism, decreased motor activity, and catatonia.
 * Both serotonin syndrome and malignant catatonia may present with signs and symptoms of delirium, autonomic instability, hyperthermia, and rigidity. Again, similar to the presentation in NMS. However, patients with Serotonin syndrome have a history of ingestion of serotonergic drugs (Ex: SSRI). These patients will also present with hyperreflexia, myoclonus, nausea, vomiting, and diarrhea.
 * Malignant hyperthermia and malignant catatonia share features of autonomic instability, hyperthermia, and rigidity. However, malignant hyperthermia is a hereditary disorder of skeletal muscle that makes these patients susceptible to exposure to halogenated anesthetics and/or depolarizing muscle relaxants like succinylcholine. Malignant hyperthermia most commonly occurs in the intraoperative or postoperative periods. Other signs and symptoms of malignant hyperthermia include metabolic and respiratory acidosis, hyperkalemia, and cardiac arrhythmias.
 * Akinetic mutism is a neurological disorder characterized by a decrease in goal-directed behavior and motivation; however, the patient has an intact level of consciousness. Patients may present with apathy, and may seem indifferent to pain, hunger, or thirst. Akinetic mutism has been associated with structural damage in a variety of brain areas. Akinetic mutism and catatonia may both manifest with immobility, mutism, and waxy flexibility. Differentiating both disorders is the fact that akinetic mutism does not present with echolalia, echopraxia, or posturing. Furthermore, it is not responsive to benzodiazepines as is the case for catatonia.
 * Elective mutism has an anxious etiology but has also been associated with personality disorders. Patients with this disorder fail to speak with some individuals but will speak with others. Likewise, they may refuse to speak in certain situations; for example, a child who refuses to speak at school but is conversational at home. This disorder is distinguished from catatonia by the absence of any other signs/symptoms.
 * Nonconvulsive status epilepticus is seizure activity with no accompanying tonic-clonic movements. It can present with stupor, similar to catatonia, and they both respond to benzodiazepines. Nonconvulsive status epilepticus is diagnosed by the presence of seizure activity seen on electroencephalogram (EEG). Catatonia on the other hand, is associated with normal EEG or diffuse slowing.
 * Delirium is characterized by fluctuating disturbed perception and consciousness in the ill individual. It has hypoactive and hyperactive or mixed forms. People with hyperactive delirium present similarly to those with excited catatonia and have symptoms of restlessness, agitation, and aggression. Those with hypoactive delirium present with similarly to retarded catatonia, withdrawn and quiet. However, catatonia also includes other distinguishing features including posturing and rigidity as well as a positive response to benzodiazepines.
 * Patients with locked-in syndrome present with immobility and mutism; however, unlike patients with catatonia who are unmotivated to communicate, patients with locked-in syndrome try to communicate with eye movements and blinking. Furthermore, locked-in syndrome is caused by damage to the brainstem.
 * Stiff-person syndrome and catatonia are similar in that they may both present with rigidity, autonomic instability and a positive response to benzodiazepines. However, stiff-person syndrome may be associated with anti-glutamic acid decarboxylase (anti-GAD) antibodies and other catatonic signs such as mutism and posturing are not part of the syndrome.
 * Untreated late-stage Parkinson's disease may present similarly to retarded catatonia with symptoms of immobility, rigidity, and difficulty speaking. Further complicating the diagnosis is the fact that many patients with Parkinson's disease will have major depressive disorder, which may be the underlying cause of catatonia. Parkinson's disease can be distinguished from catatonia by a positive response to levodopa. Catatonia on the other hand will show a positive response to benzodiazepines.
 * Extrapyramidal side effects of antipsychotic medication, especially dystonia and akathisia, can be difficult to distinguish from catatonic symptoms, or may confound them in the psychiatric setting. Extrapyramidal motor disorders usually do not involve social symptoms like negativism, while individuals with catatonic excitement typically do not have the physically painful compulsion to move that is seen in akathisia.
 * Certain stimming behaviors and stress responses in individuals with autism spectrum disorders can present similarly to catatonia. In autism spectrum disorders, chronic catatonia is distinguished by a lasting deterioration of adaptive skills from the background of pre-existing autistic symptomatology that cannot be easily explained. Acute catatonia is usually clearly distinguishable from autistic symptoms.
 * The diagnostic entities of obsessional slowness and psychogenic parkinsonism show overlapping features with catatonia, such as motor slowness, gegenhalten (oppositional paratonia), mannerisms, and reduced or absent speech. However, psychogenic parkinsonism involves tremor which is unusual in catatonia. Obsessional slowness is a controversial diagnosis, with presentations ranging from severe but common manifestations of obsessive compulsive disorder to catatonia.
 * Down Syndrome Disintegrative Disorder (or Down Syndrome Regression Disorder, DSDD / DSRD) is a chronic condition characterized by loss of previously acquired adaptive, cognitive and social functioning occurring in persons with Down Syndrome, usually during adolescence or early adulthood. The clinical picture is variable, but often includes catatonic signs, which is why it was called "catatonic psychosis" in initial reports in 1946. DSDD seems to phenotypically overlap with obsessional slowness (see above) and catatonia-like regression occurring in ASD.

Treatment
The initial treatment of catatonia is to stop medication that could be potentially leading to the syndrome. These may include steroids, stimulants, anticonvulsants, neuroleptics or dopamine blockers. A "lorazepam challenge", in which patients are given 2 mg of IV lorazepam (or another benzodiazepine) may aid in the diagnosis. Most patients with catatonia will respond significantly to this within the first 15–30 minutes. If no change is observed during the first dose, then a second dose is given and the patient is re-examined. If the patient responds to the lorazepam challenge, then lorazepam can be scheduled at interval doses until the catatonia resolves. The lorazepam must be tapered slowly, otherwise, the catatonia symptoms may return. The underlying cause of the catatonia should also be treated during this time. ECT may also be used to resolve catatonia. The success rate of ECT and lorazepam in the treatment of catatonia is estimated to be 60-100%, with earlier treatment being associated with a greater likelihood of treatment success. ECT is usually administered as multiple sessions over one-two weeks and is usually successful in those in which lorazepam fails. ECT in combination with benzodiazepines is used to treat malignant catatonia. In France, zolpidem has also been used in diagnosis, and response may occur within the same time period. Ultimately the underlying cause needs to be treated.

Supportive care is required in those with catatonia. This includes monitoring vital signs and fluid status, and in those with chronic symptoms; maintaining nutrition and hydration, medications to prevent a blood clot, and measures to prevent the development of pressure ulcers.

Electroconvulsive therapy (ECT) is an effective treatment for catatonia that is well acknowledged. ECT has also shown favorable outcomes in patients with chronic catatonia. However, it has been pointed out that further high quality randomized controlled trials are needed to evaluate the efficacy, tolerance, and protocols of ECT in catatonia.

Antipsychotics are sometimes used in those with a co-existing psychosis, however they should be used with care as they may worsen catatonia and have a risk of neuroleptic malignant syndrome, a dangerous condition that can mimic catatonia and requires immediate discontinuation of the antipsychotic.

There is evidence that clozapine works better than other antipsychotics to treat catatonia.

Excessive glutamate activity is believed to be involved in catatonia; when first-line treatment options fail, NMDA antagonists such as amantadine or memantine may be used. Amantadine may have an increased incidence of tolerance with prolonged use and can cause psychosis, due to its additional effects on the dopamine system. Memantine has a more targeted pharmacological profile for the glutamate system, reduced incidence of psychosis and may therefore be preferred for individuals who cannot tolerate amantadine. Topiramate is another treatment option for resistant catatonia; it produces its therapeutic effects by producing glutamate antagonism via modulation of AMPA receptors.

Prognosis
Twenty-five percent of psychiatric patients with catatonia will have more than one episode throughout their lives. Treatment response for patients with catatonia is 50–70%, with treatment failure being associated with a poor prognosis. Many of these patients will require long-term and continuous mental health care. For patients with catatonia with underlying schizophrenia, the prognosis is much poorer.

Epidemiology
Catatonia has been historically studied in psychiatric patients. Catatonia is underrecognized and the features may be mistaken for other disorders (such as negative symptoms of schizophrenia), leading to an underestimate of the prevalence. The prevalence has been reported to be as high as 10% in those with acute psychiatric illnesses, and 9-30% in the setting of inpatient psychiatric care. One large population estimate has suggested that the incidence of catatonia is 10.6 episodes per 100 000 person-years. It occurs in males and females in approximately equal numbers. 21-46% of all catatonia cases can be attributed to a general medical condition.

History
Reports of stupor-like and catatonia-like states abound in the history of psychiatry. After the middle of the 19th century there was an increase of interest in the motor disorders accompanying madness, culminating in the publication by Karl Ludwig Kahlbaum in 1874 of Die Katatonie oder das Spannungsirresein ("Catatonia or Tension Insanity").

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title: Catatonia


text:
Cipher

In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. To encipher or encode is to convert information into cipher or code. In common parlance, "cipher" is synonymous with "code", as they are both a set of steps that encrypt a message; however, the concepts are distinct in cryptography, especially classical cryptography.

Codes generally substitute different length strings of characters in the output, while ciphers generally substitute the same number of characters as are input. A code maps one meaning with another. Words and phrases can be coded as letters or numbers. Codes typically have direct meaning from input to key. Codes primarily function to save time. Ciphers are algorithmic. The given input must follow the cipher's process to be solved. Ciphers are commonly used to encrypt written information.

Codes operated by substituting according to a large codebook which linked a random string of characters or numbers to a word or phrase. For example, "UQJHSE" could be the code for "Proceed to the following coordinates." When using a cipher the original information is known as plaintext, and the encrypted form as ciphertext. The ciphertext message contains all the information of the plaintext message, but is not in a format readable by a human or computer without the proper mechanism to decrypt it.

The operation of a cipher usually depends on a piece of auxiliary information, called a key (or, in traditional NSA parlance, a cryptovariable). The encrypting procedure is varied depending on the key, which changes the detailed operation of the algorithm. A key must be selected before using a cipher to encrypt a message. Without knowledge of the key, it should be extremely difficult, if not impossible, to decrypt the resulting ciphertext into readable plaintext.

Most modern ciphers can be categorized in several ways:

 * By whether they work on blocks of symbols usually of a fixed size (block ciphers), or on a continuous stream of symbols (stream ciphers).
 * By whether the same key is used for both encryption and decryption (symmetric key algorithms), or if a different key is used for each (asymmetric key algorithms). If the algorithm is symmetric, the key must be known to the recipient and sender and to no one else. If the algorithm is an asymmetric one, the enciphering key is different from, but closely related to, the deciphering key. If one key cannot be deduced from the other, the asymmetric key algorithm has the public/private key property and one of the keys may be made public without loss of confidentiality.

Etymology
Originating from the Arabic word for zero صفر (sifr), the word "cipher" spread to Europe as part of the Arabic numeral system during the Middle Ages. The Roman numeral system lacked the concept of 0|zero, and this limited advances in mathematics. In this transition, the word was adopted into Medieval Latin as cifra, and then into Middle French as cifre. This eventually led to the English word cipher (minority spelling cypher). One theory for how the term came to refer to encoding is that the concept of zero was confusing to Europeans, and so the term came to refer to a message or communication that was not easily understood.

The term cipher was later also used to refer to any Arabic digit, or to calculation using them, so encoding text in the form of Arabic numerals is literally converting the text to "ciphers".

Versus codes
In casual contexts, "code" and "cipher" can typically be used interchangeably; however, the technical usages of the words refer to different concepts. Codes contain meaning; words and phrases are assigned to numbers or symbols, creating a shorter message.

An example of this is the commercial telegraph code which was used to shorten long telegraph messages which resulted from entering into commercial contracts using exchanges of telegrams.

Another example is given by whole word ciphers, which allow the user to replace an entire word with a symbol or character, much like the way written Japanese utilizes Kanji (meaning Chinese characters in Japanese) characters to supplement the native Japanese characters representing syllables. An example using English language with Kanji could be to replace "The quick brown fox jumps over the lazy dog" by "The quick brown 狐 jumps 上 the lazy 犬". Stenographers sometimes use specific symbols to abbreviate whole words.

Ciphers, on the other hand, work at a lower level: the level of individual letters, small groups of letters, or, in modern schemes, individual bits and blocks of bits. Some systems used both codes and ciphers in one system, using superencipherment to increase the security. In some cases the terms codes and ciphers are used synonymously with substitution and transposition, respectively.

Historically, cryptography was split into a dichotomy of codes and ciphers, while coding had its own terminology analogous to that of ciphers: "encoding, codetext, decoding" and so on.

However, codes have a variety of drawbacks, including susceptibility to cryptanalysis and the difficulty of managing a cumbersome codebook. Because of this, codes have fallen into disuse in modern cryptography, and ciphers are the dominant technique.

Types
There are a variety of different types of encryption. Algorithms used earlier in the history of cryptography are substantially different from modern methods, and modern ciphers can be classified according to how they operate and whether they use one or two keys.

Historical
The Caesar Cipher is one of the earliest known cryptographic systems. Julius Caesar used a cipher that shifts the letters in the alphabet in place by three and wrapping the remaining letters to the front to write to Marcus Tullius Cicero in approximately 50 BC.

Historical pen and paper ciphers used in the past are sometimes known as classical ciphers. They include simple substitution ciphers (such as ROT13) and transposition ciphers (such as a Rail Fence Cipher). For example, "GOOD DOG" can be encrypted as "PLLX XLP" where "L" substitutes for "O", "P" for "G", and "X" for "D" in the message. Transposition of the letters "GOOD DOG" can result in "DGOGDOO". These simple ciphers and examples are easy to crack, even without plaintext-ciphertext pairs.

In the 1640s, the Parliamentarian commander, Edward Montagu, 2nd Earl of Manchester, developed ciphers to send coded messages to his allies during the English Civil War.

Simple ciphers were replaced by polyalphabetic substitution ciphers (such as the Vigenère) which changed the substitution alphabet for every letter. For example, "GOOD DOG" can be encrypted as "PLSX TWF" where "L", "S", and "W" substitute for "O". With even a small amount of known or estimated plaintext, simple polyalphabetic substitution ciphers and letter transposition ciphers designed for pen and paper encryption are easy to crack. It is possible to create a secure pen and paper cipher based on a one-time pad, but these have other disadvantages.

During the early twentieth century, electro-mechanical machines were invented to do encryption and decryption using transposition, polyalphabetic substitution, and a kind of "additive" substitution. In rotor machines, several rotor disks provided polyalphabetic substitution, while plug boards provided another substitution. Keys were easily changed by changing the rotor disks and the plugboard wires. Although these encryption methods were more complex than previous schemes and required machines to encrypt and decrypt, other machines such as the British Bombe were invented to crack these encryption methods.

Modern
Modern encryption methods can be divided by two criteria: by type of key used, and by type of input data.

By type of key used ciphers are divided into:
 * symmetric key algorithms (Private-key cryptography), where one same key is used for encryption and decryption, and
 * AES (Rijndael) Round Function.pngetric key algorithms (Public-key cryptography), where two different keys are used for encryption and decryption.

In a symmetric key algorithm (e.g., DES and AES), the sender and receiver must have a shared key set up in advance and kept secret from all other parties; the sender uses this key for encryption, and the receiver uses the same key for decryption. The design of AES (Advanced Encryption System) was beneficial because it aimed to overcome the flaws in the design of the DES (Data encryption standard). AES's designer's claim that the common means of modern cipher cryptanalytic attacks are ineffective against AES due to its design structure.[12]

Ciphers can be distinguished into two types by the type of input data:
 * block ciphers, which encrypt block of data of fixed size, and
 * stream ciphers, which encrypt continuous streams of data.

Key size and vulnerability
In a pure mathematical attack, (i.e., lacking any other information to help break a cipher) two factors above all count:

Since the desired effect is computational difficulty, in theory one would choose an algorithm and desired difficulty level, thus decide the key length accordingly.
 * Computational power available, i.e., the computing power which can be brought to bear on the problem. It is important to note that average performance/capacity of a single computer is not the only factor to consider. An adversary can use multiple computers at once, for instance, to increase the speed of exhaustive search for a key (i.e., "brute force" attack) substantially.
 * Key size, i.e., the size of key used to encrypt a message. As the key size increases, so does the complexity of exhaustive search to the point where it becomes impractical to crack encryption directly.

An example of this process can be found at Key Length which uses multiple reports to suggest that a symmetrical cipher with 128 bits, an asymmetric cipher with 3072 bit keys, and an elliptic curve cipher with 256 bits, all have similar difficulty at present.

Claude Shannon proved, using information theory considerations, that any theoretically unbreakable cipher must have keys which are at least as long as the plaintext, and used only once: one-time pad.

title: Cipher