Amnesia is a deficit in
memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
caused by
brain damage
Neurotrauma, brain damage or brain injury (BI) is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors. In general, brain damage refers to significant, undiscriminating t ...
or disease,
[Gazzaniga, M., Ivry, R., & Mangun, G. (2009) Cognitive Neuroscience: The biology of the mind. New York: W.W. Norton & Company.] but it can also be caused temporarily by the use of various
sedative
A sedative or tranquilliser is a substance that induces sedation by reducing irritability or excitement. They are CNS depressants and interact with brain activity causing its deceleration. Various kinds of sedatives can be distinguished, but t ...
s and
hypnotic
Hypnotic (from Greek ''Hypnos'', sleep), or soporific drugs, commonly known as sleeping pills, are a class of (and umbrella term for) psychoactive drugs whose primary function is to induce sleep (or surgical anesthesiaWhen used in anesthesia ...
drug
A drug is any chemical substance that causes a change in an organism's physiology or psychology when consumed. Drugs are typically distinguished from food and substances that provide nutritional support. Consumption of drugs can be via insuffla ...
s. The memory can be either wholly or partially lost due to the extent of damage that was caused. There are two main types of amnesia:
retrograde amnesia
In neurology, retrograde amnesia (RA) is a loss of memory-access to events that occurred or information that was learned in the past. It is caused by an injury or the onset of a disease. It tends to negatively affect episodic, autobiographical, ...
and
anterograde amnesia
In neurology, anterograde amnesia is the inability to create new memories after the event that caused amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact. T ...
. Retrograde amnesia is the inability to retrieve information that was acquired before a particular date, usually the date of an accident or operation. In some cases the memory loss can extend back decades, while in others the person may lose only a few months of memory. Anterograde amnesia is the inability to transfer new information from the
short-term store into the
long-term store. People with anterograde amnesia cannot remember things for long periods of time. These two types are not mutually exclusive; both can occur simultaneously.
Case studies also show that amnesia is typically associated with damage to the
medial temporal lobe
The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.
The temporal lobe is involved in proc ...
. In addition, specific areas of the
hippocampus
The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
(the
CA1 region) are involved with memory. Research has also shown that when areas of the
diencephalon
The diencephalon (or interbrain) is a division of the forebrain (embryonic ''prosencephalon''). It is situated between the telencephalon and the midbrain (embryonic ''mesencephalon''). The diencephalon has also been known as the 'tweenbrain in ol ...
are damaged, amnesia can occur. Recent studies have shown a correlation between
deficiency of RbAp48 protein and memory loss
Memory is commonly referred to as the ability to encode, store, retain and subsequently recall information and past experiences in the human brain. This process involves many proteins, one of which is the Histone-binding protein RbAp48 (also known ...
. Scientists were able to find that mice with damaged memory have a lower level of RbAp48 protein compared to normal, healthy mice. In people with amnesia, the ability to recall ''immediate information'' is still retained, and they may still be able to form new memories. However, a severe reduction in the ability to learn new material and retrieve old information can be observed. People can learn new procedural knowledge. In addition,
priming
Priming may refer to:
* Priming (agriculture), a form of seed planting preparation, in which seeds are soaked before planting
* Priming (immunology), a process occurring when a specific antigen is presented to naive lymphocytes causing them to di ...
(both perceptual and conceptual) can assist amnesiacs in the learning of fresh
non-declarative knowledge.
Individuals with amnesia also retain substantial intellectual, linguistic, and social skill despite profound impairments in the ability to recall specific information encountered in prior learning episodes.
The term is ; .
Signs and symptoms
Individuals with amnesia can learn new information, particularly if the information is non-declarative knowledge. However, in some situations, people with dense anterograde amnesia do not remember the episodes during which they previously learned or observed the information. Some people with amnesia show abnormal amounts of memory loss, confusion, and difficulty recalling other people or places. People who recover often do not remember having amnesia.
Declarative information
Declarative memory can be broken down into semantic memory and episodic memory, semantic memory being that of facts, episodic memory being that of memory related to events.
While a patient with amnesia might have a loss of declarative memory, this loss might vary in severity as well as the declarative information that it affects, depending on many factors. For example, LSJ was a patient that had retrograde declarative memory loss as the result of bilateral medial temporal lobe damage, but she was still able to remember how to perform some declarative skills. She was able to remember how to read music and the techniques used in art. She had preserved skill-related declarative memory for some things even though she had deficits in other declarative memory tasks. She even scored higher on skill-related declarative memory than the control in watercolor techniques, a technique that she used in her professional career before she acquired amnesia.
Semantic Information
The loss of semantic information in amnesia is most closely related with damage to the medial temporal lobe or to the neocortex.
Some patients with anterograde amnesia can still acquire some
semantic
Semantics (from grc, σημαντικός ''sēmantikós'', "significant") is the study of reference, meaning, or truth. The term can be used to refer to subfields of several distinct disciplines, including philosophy, linguistics and comput ...
information, even though it might be more difficult and might remain rather unrelated to more general knowledge. H.M. could accurately draw a floor plan of the home in which he lived after surgery, even though he had not lived there in years. There is evidence that the hippocampus and the medial temporal lobe may help to consolidate semantic memories, but then they are more correlated with the neocortex. While lesions of the hippocampus normally lead to the loss of episodic memory, if there is any effect on semantic memory, it is more varied and usually does not last as long.
Episodic Information
One reason that patients could not form new episodic memories is likely because the
CA1 region of the hippocampus has a
lesion
A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals.
Types
There is no designated classifi ...
, and thus the hippocampus could not make connections to the cortex. After an
ischemic
Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems wi ...
episode (an interruption of the blood flow to the brain), an MRI of patient R.B. following surgery showed his hippocampus to be intact except for a specific lesion restricted to the CA1 pyramidal cells.
In one instance, transient global amnesia was caused by a hippocampal CA1 lesion. While this was a temporary case of amnesia, it still shows the importance of the CA1 region of the hippocampus in memory. Episodic memory loss is most likely to occur when there has been damage to the hippocampus. There is evidence that damage to the medial temporal lobe correlates to a loss of autobiographical episodic memory.
Non-declarative information
Some retrograde and anterograde amnesiacs are capable of non-declarative memory, including implicit learning and procedural learning. For example, some patients show improvement on the
pseudorandom
A pseudorandom sequence of numbers is one that appears to be statistically random, despite having been produced by a completely deterministic
Determinism is a philosophical view, where all events are determined completely by previously exi ...
sequences experiment just as healthy people; therefore, procedural learning can proceed independently of the brain system required for declarative memory. Some patients with amnesia are able to remember skills that they had learned without being able to consciously recall where they had learned that information. For example, they may learn to do a task and then be able to perform the task later without any recollection of learning the task. According to
fMRI
Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
studies, the acquisition of procedural memories activates the
basal ganglia
The basal ganglia (BG), or basal nuclei, are a group of subcortical nuclei, of varied origin, in the brains of vertebrates. In humans, and some primates, there are some differences, mainly in the division of the globus pallidus into an extern ...
, the
premotor cortex
The premotor cortex is an area of the motor cortex lying within the frontal lobe of the brain just anterior to the primary motor cortex. It occupies part of Brodmann's area 6. It has been studied mainly in primates, including monkeys and humans. ...
and the supplementary motor area, regions which are not normally associated with the formation of declarative memories. This type of dissociation between declarative and procedural memory can also be found in patients with diencephalic amnesia such as
Korsakoff's syndrome
Korsakoff syndrome (KS) is a disorder of the central nervous system characterized by amnesia, deficits in explicit memory, and confabulation. This neurological disorder is caused by a deficiency of thiamine (vitamin B1) in the brain, and it is ...
. Another example demonstrated by some patients, such as K.C. and H.M, who have medial temporal damage and anterograde amnesia, still have perceptual priming. Priming was accomplished in many different experiments of amnesia, and it was found that the patients can be primed; they have no conscious recall of the event, but the response is there. Those patients did well in th
word fragment completion task There is some evidence that non-declarative memory can be held onto in the form of motor skills. This idea was disputed, though, because it is argued that motor skills require both declarative and non-declarative information.
Causes
There are three generalized categories in which amnesia could be acquired by a person. The three categories are
head trauma
A head injury is any injury that results in trauma to the skull or brain. The terms ''traumatic brain injury'' and ''head injury'' are often used interchangeably in the medical literature. Because head injuries cover such a broad scope of inju ...
(example: head injuries), traumatic events (example: seeing something devastating to the mind), or physical deficiencies (example:
atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations (which can destroy the gene to build up the organ), poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply t ...
of the
hippocampus
The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
). The majority of amnesia and related memory issues derive from the first two categories as these are more common and the third could be considered a subcategory of the first.
* Head trauma is a very broad range as it deals with any kind of injury or active action toward the brain which might cause amnesia. Retrograde and anterograde amnesia is more often seen from events like this, an exact example of a cause of the two would be
electroconvulsive therapy
Electroconvulsive therapy (ECT) is a psychiatry, psychiatric treatment where a generalized seizure (without muscular convulsions) is electrically induced to manage refractory mental disorders.Rudorfer, MV, Henry, ME, Sackeim, HA (2003)"Electroco ...
, which would cause both briefly for the receiving patient.
* Traumatic events are more subjective. What is traumatic is dependent on what the person finds to be traumatic. Regardless, a traumatic event is an event where something so distressing occurs that the mind chooses to forget rather than deal with the stress. A common example of amnesia that is caused by traumatic events is
dissociative amnesia
Psychogenic amnesia or dissociative amnesia is a memory disorder characterized by sudden retrograde episodic memory loss, said to occur for a period of time ranging from hours to years to decades. More recently, "dissociative amnesia" has been d ...
, which occurs when the person forgets an event that has deeply disturbed them. An example would be a person forgetting a fatal and graphic car accident involving their loved ones.
* Physical deficiencies are different from head trauma because physical deficiencies lean more toward passive physical issues. Examples of physical deficiencies include
Alzheimer's disease
Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...
,
neurological paraneoplastic syndromes such as
anti-NMDA receptor encephalitis
Anti-NMDA receptor encephalitis is a type of encephalitis, brain inflammation caused by antibodies. Early symptoms may include fever, headache, and feeling tired. This is then typically followed by psychosis which presents with delusions, false b ...
, and
vitamin B12 deficiency
Vitamin B12 deficiency, also known as cobalamin deficiency, is the medical condition in which the blood and tissue have a lower than normal level of vitamin B12. Symptoms can vary from none to severe. Mild deficiency may have few or absent symp ...
.
Among specific causes of amnesia are the following:
*
Electroconvulsive therapy
Electroconvulsive therapy (ECT) is a psychiatry, psychiatric treatment where a generalized seizure (without muscular convulsions) is electrically induced to manage refractory mental disorders.Rudorfer, MV, Henry, ME, Sackeim, HA (2003)"Electroco ...
in which seizures are electrically induced in patients for therapeutic effect can have acute effects including both retrograde and anterograde amnesia.
[Benbow, SM (2004) "Adverse effects of ECT". In AIF Scott (ed.]
''The ECT Handbook, second edition.''
London: The Royal College of Psychiatrists, pp. 170–174.
*
Alcohol
Alcohol most commonly refers to:
* Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom
* Alcohol (drug), an intoxicant found in alcoholic drinks
Alcohol may also refer to:
Chemicals
* Ethanol, one of sev ...
can both cause
blackouts and have deleterious
effects on memory formation.
Diagnosis
Types
*
Anterograde amnesia
In neurology, anterograde amnesia is the inability to create new memories after the event that caused amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact. T ...
is the inability to create new memories due to brain damage, while long-term memories from before the event remain intact. The brain damage can be caused by the effects of long-term alcoholism, severe
malnutrition
Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is "a deficiency, excess, or imbalance of energy, protein and other nutrients" which adversely affects the body's tissues a ...
,
stroke
A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
,
head trauma
A head injury is any injury that results in trauma to the skull or brain. The terms ''traumatic brain injury'' and ''head injury'' are often used interchangeably in the medical literature. Because head injuries cover such a broad scope of inju ...
,
encephalitis
Encephalitis is inflammation of the brain. The severity can be variable with symptoms including reduction or alteration in consciousness, headache, fever, confusion, a stiff neck, and vomiting. Complications may include seizures, hallucinations, ...
, surgery,
Wernicke–Korsakoff syndrome
Wernicke–Korsakoff syndrome (WKS) is the combined presence of Wernicke encephalopathy (WE) and Korsakoff syndrome. Due to the close relationship between these two disorders, people with either are usually diagnosed with WKS as a single syndrome ...
,
cerebrovascular events,
anoxia or other trauma. The two brain regions related with this condition are
medial temporal lobe
The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.
The temporal lobe is involved in proc ...
and medial diencephalon. Anterograde amnesia cannot be treated with pharmacological methods due to neuronal loss.
However, treatment exists in educating patients to define their daily routines and after several steps they begin to benefit from their procedural memory. Procedural memory can be intact even when other forms of memory is not, although not always the case. Likewise, social and emotional support is critical to improving
quality of life
Quality of life (QOL) is defined by the World Health Organization as "an individual's perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards ...
for those with anterograde amnesia.
[ Fentanyl use by opioid users has been identified as a potential cause in a cluster of cases that occurred in Boston, MA.
* ]Retrograde amnesia
In neurology, retrograde amnesia (RA) is a loss of memory-access to events that occurred or information that was learned in the past. It is caused by an injury or the onset of a disease. It tends to negatively affect episodic, autobiographical, ...
is inability to recall memories before onset of amnesia. One may be able to encode new memories after the incident. Retrograde is usually caused by head trauma or brain damage to parts of the brain besides the hippocampus. The hippocampus is responsible for encoding new memory. Episodic memory
Episodic memory is the memory of everyday events (such as times, location geography, associated emotions, and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred ...
is more likely to be affected than semantic memory
Semantic memory refers to general world knowledge that humans have accumulated throughout their lives. This general knowledge (word meanings, concepts, facts, and ideas) is intertwined in experience and dependent on culture. We can learn about n ...
. The damage is usually caused by head trauma, cerebrovascular
Cerebrovascular disease includes a variety of Medicine, medical conditions that affect the blood vessels of the brain and the cerebral circulation. Arteries supplying oxygen and nutrients to the brain are often Angiopathy, damaged or deformed in ...
accident, stroke, tumor
A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
, hypoxia
Hypoxia means a lower than normal level of oxygen, and may refer to:
Reduced or insufficient oxygen
* Hypoxia (environmental), abnormally low oxygen content of the specific environment
* Hypoxia (medical), abnormally low level of oxygen in the tis ...
, encephalitis
Encephalitis is inflammation of the brain. The severity can be variable with symptoms including reduction or alteration in consciousness, headache, fever, confusion, a stiff neck, and vomiting. Complications may include seizures, hallucinations, ...
, or chronic alcoholism
Alcoholism is, broadly, any drinking of alcohol that results in significant mental or physical health problems. Because there is disagreement on the definition of the word ''alcoholism'', it is not a recognized diagnostic entity. Predomina ...
. People with retrograde amnesia are more likely to remember general knowledge rather than specifics. Recent memories are less likely to be recovered, but older memories will be easier to recall due to strengthening over time
Retrograde amnesia
is usually temporary and can be treated by exposing them to memories from the loss. Another type of consolidation (process by which memories become stable in the brain) occurs over much longer periods of time/days, weeks, months and years and likely involves transfer of information from the hippocampus to more permanent storage site in the cortex. The operation of this longer-term consolidation process is seen in the retrograde amnesia of patients with hippocampal damage who can recall memories from childhood relatively normally, but are impaired when recalling experiences that occurred just a few years prior to the time they became amnesic. (Kirwan et al.,2008)In the case of LSJ, her case shows that retrograde amnesia can affect many different parts of knowledge. LSJ was not able to remember things from her child or adult life. She was not able to remember things that most people pick up in everyday life such as logos or the names of common songs.
* Post-traumatic amnesia
Post-traumatic amnesia (PTA) is a state of confusion that occurs immediately following a traumatic brain injury (TBI) in which the injured person is disoriented and unable to remember events that occur after the injury.
The person may be unable ...
is generally due to a head injury
A head injury is any injury that results in trauma to the skull or brain. The terms ''traumatic brain injury'' and ''head injury'' are often used interchangeably in the medical literature. Because head injuries cover such a broad scope of inju ...
(example: a fall, a knock on the head). Traumatic amnesia is often transient, but may be permanent or either anterograde, retrograde, or mixed type. The extent of the period covered by the amnesia is related to the degree of injury and may give an indication of the prognosis for recovery of other functions. Mild trauma, such as a car accident that results in no more than mild whiplash, might cause the occupant of a car to have no memory of the moments just before the accident due to a brief interruption in the short/long-term memory transfer mechanism. The patient may also lose knowledge of who people are. Having longer periods of amnesia or consciousness after an injury may be an indication that recovery from remaining concussion symptoms will take much longer.
* Dissociative amnesia
Psychogenic amnesia or dissociative amnesia is a memory disorder characterized by sudden retrograde episodic memory loss, said to occur for a period of time ranging from hours to years to decades. More recently, "dissociative amnesia" has been d ...
results from a psychological cause as opposed to direct damage to the brain caused by head injury, physical trauma or disease, which is known as organic amnesia. Individuals with organic amnesia have difficulty with emotion expression as well as undermining the seriousness of their condition. The damage to the memory is permanent. Dissociative amnesia can include:
** Repressed memory
Repressed memory is an inability to recall autobiographical information, usually of a traumatic or stressful nature. The concept originated in psychoanalytic theory where repression is defined as a protective mechanism that excludes memory of ...
is the inability to recall information, usually about stressful or traumatic events in persons' lives, such as a violent attack or disaster. The memory is stored in long-term memory, but access to it is impaired because of psychological defense mechanisms. Persons retain the capacity to learn new information and there may be some later partial or complete recovery of memory. Formerly known as "Psychogenic Amnesia".
** Dissociative fugue
Dissociative fugue (), formerly called a fugue state or psychogenic fugue, is a mental disorder, mental and Abnormal behavior, behavioral Disorder (medicine), disorderDrs; that is nosology, classified variously as a dissociative disorder,Dissoci ...
(''formerly'' psychogenic fugue) is also known as fugue state. It is caused by psychological trauma, is usually temporary and unresolved, and therefore, may return. It must exist outside the influence of pre-existing medical conditions, such as a lobotomy, and immediate influence of any mind-altering substances, such as alcohol or drugs. An individual with dissociative fugue disorder either completely forgets or is confused about their identity, and may even assume a new one. They can travel hundreds miles from their home or work; they can also engage in other uncharacteristic, and occasionally unsafe, behavior. For example, two men in a study of five individuals with dissociative fugue had engaged in criminal activity while in their fugue state, having had no criminal record before the episodes. While popular in fiction, this type of amnesia is extremely rare.
** Posthypnotic amnesia
Post-hypnotic amnesia is the inability in hypnotic subjects to recall events that took place while under hypnosis. This can be achieved by giving individuals a suggestion during hypnosis to forget certain material that they have learned either befo ...
occurs when events during hypnosis
Hypnosis is a human condition involving focused attention (the selective attention/selective inattention hypothesis, SASI), reduced peripheral awareness, and an enhanced capacity to respond to suggestion.In 2015, the American Psychologica ...
are forgotten, or where memories are unable to be recalled. The failure to remember those events is induced by suggestions made during the hypnosis. Some characteristics of posthypnotic amnesia include inability to remember specific events while under hypnotic influence, reversibility, and having no relation between the implicit and explicit memory. Research has shown that there could be selectivity with amnesia when posthypnotic amnesia occurs.
* Lacunar amnesia
Lacunar amnesia is the loss of memory about a specific event. This specific form of amnesia is caused by brain damage in the limbic system which is responsible for our memories and emotions. When the damage occurs it leaves a lacuna, or a gap, in ...
is the loss of memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
about one specific event. It is a type of amnesia that leaves a lacuna (a gap) in the record of memory in the cortex region of the brain. The cause of this type of amnesia is the result of brain damage to the limbic system which control our memories and emotions.
* Childhood amnesia
Childhood amnesia, also called infantile amnesia, is the inability of adults to retrieve episodic memories (memories of situations or events) before the age of two to four years, as well as the period before the age of ten of which some older adul ...
(also known as infantile amnesia) is the common inability to remember events from one's own childhood. Sigmund Freud
Sigmund Freud ( , ; born Sigismund Schlomo Freud; 6 May 1856 – 23 September 1939) was an Austrian neurologist and the founder of psychoanalysis, a clinical method for evaluating and treating psychopathology, pathologies explained as originatin ...
notoriously attributed this to sexual repression
Sexual repression is a state in which a person is prevented from expressing their own sexuality. Sexual repression is often linked with feelings of guilt or shame being associated with sexual impulses. Defining characteristics and practices asso ...
, while modern scientific approaches generally attribute it to aspects of brain development
The development of the nervous system, or neural development (neurodevelopment), refers to the processes that generate, shape, and reshape the nervous system of animals, from the earliest stages of embryonic development to adulthood. The fiel ...
or developmental psychology
Developmental psychology is the science, scientific study of how and why humans grow, change, and adapt across the course of their lives. Originally concerned with infants and children, the field has expanded to include adolescence, adult deve ...
, including language development
Language development in humans is a process starting early in life. Infants start without knowing a language, yet by 10 months, babies can distinguish speech sounds and engage in babbling. Some research has shown that the earliest learning begin ...
, which may be why people do not easily remember pre-language events. Some research states that most adults cannot remember memories as early as two or three years old. Research suggests there are cultural influences that affect memories that are recalled. Researchers have found that implicit memories cannot be recalled or described. Remembering how to play the piano is a common example of implicit memory, as are walking, speaking, and other everyday activities that would be difficult to focus on if they had to be relearned every time one got up in the morning. Explicit memories, on the other hand, can be recalled and described in words. Remembering the first time meeting a teacher is an example of an explicit memory.
* Transient global amnesia
Transient global amnesia (TGA) is a neurological disorder whose key defining characteristic is a temporary but almost total disruption of short-term memory with a range of problems accessing older memories. A person in a state of TGA exhibits no o ...
is a well-described medical and clinical phenomenon. This form of amnesia is distinct in that abnormalities in the hippocampus
The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
can sometimes be visualized using a special form of magnetic resonance imaging
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...
of the brain known as diffusion-weighted imaging
Diffusion-weighted magnetic resonance imaging (DWI or DW-MRI) is the use of specific MRI sequences as well as software that generates images from the resulting data that uses the diffusion of water molecules to generate contrast in MR images. It ...
(DWI). Symptoms typically last for less than a day and there is often no clear precipitating factor or any other neurological deficits. The cause of this syndrome is not clear. The hypothesis of the syndrome includes transient reduced blood flow, possible seizure
An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with los ...
or an atypical type of a migraine
Migraine (, ) is a common neurological disorder characterized by recurrent headaches. Typically, the associated headache affects one side of the head, is pulsating in nature, may be moderate to severe in intensity, and could last from a few hou ...
. Patients are typically amnestic of events more than a few minutes in the past, though immediate recall is usually preserved.
* Source amnesia Source amnesia is the inability to remember where, when or how previously learned information has been acquired, while retaining the factual knowledge. This branch of amnesia is associated with the malfunctioning of one's explicit memory. It is lik ...
is the inability to remember where, when or how previously learned information has been acquired, while retaining the factual knowledge. When individuals are unable to remember, false memories can occur and cause great confusion.
* Korsakoff's syndrome
Korsakoff syndrome (KS) is a disorder of the central nervous system characterized by amnesia, deficits in explicit memory, and confabulation. This neurological disorder is caused by a deficiency of thiamine (vitamin B1) in the brain, and it is ...
can result from long-term alcoholism or malnutrition. It is caused by brain damage due to a vitamin B1 deficiency and will be progressive if alcohol intake and nutrition pattern are not modified. Other neurological problems are likely to be present in combination with this type of Amnesia, such as problems with the medial temporal lobe and frontal lobe dysfunction. Korsakoff's syndrome is also known to be connected with confabulation
In psychology, confabulation is a memory error defined as the production of fabricated, distorted, or misinterpreted memories about oneself or the world. It is generally associated with certain types of brain damage (especially aneurysm in the a ...
. The person's short-term memory may appear to be normal, but the person may have a difficult time attempting to recall a past story, or with unrelated words, as well as complicated patterns. Korsakoff's syndrome is unique because it involves both anterograde and retrograde amnesia.
* Drug-induced amnesia
Drug-induced amnesia is amnesia caused by drugs. Amnesia may be therapeutic for medical treatment or for medical procedures, or it may be a side-effect of a drug, such as alcohol, or certain medications for psychiatric disorders, such as benzodiaz ...
is intentionally caused by injection of an amnestic drug to help a patient forget surgery or medical procedures, particularly those not performed under full anesthesia
Anesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), ...
, or likely to be particularly traumatic. Such drugs are also referred to as "premedicants". Most commonly, a 2-halogenated benzodiazepine
Benzodiazepines (BZD, BDZ, BZs), sometimes called "benzos", are a class of depressant drugs whose core chemical structure is the fusion of a benzene ring and a diazepine ring. They are prescribed to treat conditions such as anxiety disorders, ...
such as midazolam
Midazolam, sold under the brand name Versed among others, is a benzodiazepine medication used for anesthesia and procedural sedation, and to treat severe agitation. It works by inducing sleepiness, decreasing anxiety, and causing a loss of a ...
or flunitrazepam
Flunitrazepam, also known as Rohypnol among other names, is a benzodiazepine used to treat severe insomnia and assist with anesthesia. As with other hypnotics, flunitrazepam has been advised to be prescribed only for short-term use or by those ...
is the drug of choice, although other strongly amnestic drugs such as propofol
Propofol, marketed as Diprivan, among other names, is a short-acting medication that results in a decreased level of consciousness and a lack of memory for events. Its uses include the starting and maintenance of general anesthesia, sedation f ...
or scopolamine
Scopolamine, also known as hyoscine, or Devil's Breath, is a natural or synthetically produced tropane alkaloid and anticholinergic drug that is formally used as a medication for treating motion sickness and postoperative nausea and vomiting ...
may also be used for this application. Memories of the short time-frame in which the procedure was performed are permanently lost or at least substantially reduced, but once the drug wears off, memory is no longer affected.
* Situation-specific amnesia can arise in a variety of circumstances (for example, committing an offence, child sexual abuse
Child sexual abuse (CSA), also called child molestation, is a form of child abuse in which an adult or older adolescent uses a child for sexual stimulation. Forms of child sexual abuse include engaging in sexual activities with a child (whet ...
) resulting in PTSD
Post-traumatic stress disorder (PTSD) is a mental and behavioral disorder that can develop because of exposure to a traumatic event, such as sexual assault, warfare, traffic collisions, child abuse, domestic violence, or other threats on a ...
. It has been claimed that it involves a narrowing of consciousness with attention focused on central perceptual details and/or that the emotional or traumatic events are processed differently from ordinary memories.
* Transient epileptic amnesia is a rare and unrecognized form of temporal lobe epilepsy
Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrical ...
, which is typically an episodic isolated memory loss. It has been recognized as a treatment-responsive syndrome congenial to anti-epileptic drugs.
* Semantic amnesia affects semantic memory and primarily expresses itself in the form of problems with language use and acquisition. Semantic amnesia can lead to dementia.
* Pseudodementia
Pseudodementia (otherwise known as depression-related cognitive dysfunction) is a condition where mental cognition can be temporarily decreased. The term pseudodementia is applied to the range of functional psychiatric conditions such as depressi ...
(otherwise known as depression-related cognitive dysfunction) is a condition where mental cognition can be temporarily decreased. The term pseudodementia is applied to the range of functional psychiatric conditions such as depression and schizophrenia, that may mimic organic dementia, but are essentially reversible on treatment. Pseudodementia typically involves three cognitive components: memory issues, deficits in executive functioning, and deficits in speech and language. Specific cognitive symptoms might include trouble recalling words or remembering things in general, decreased attentional control and concentration, difficulty completing tasks or making decisions, decreased speed and fluency of speech, and impaired processing speed. People with pseudodementia are typically very distressed about the cognitive impairment they experience. With in this condition, there are two specific treatments that have been found to be effective for the treatment of depression, and these treatments may also be beneficial in the treatment of pseudodementia. Cognitive behavioral therapy (CBT) involves exploring and changing thought patterns and behaviors in order to improve one's mood. Interpersonal therapy focuses on the exploration of an individual's relationships and identifying any ways in which they may be contributing to feelings of depression.
Treatment
Many forms of amnesia fix themselves without being treated. However, there are a few ways to cope with memory loss if treatment is needed. Since there are a variety of causes that form different amnesia, it is important to note that there are different methods that response better with the certain type of amnesia. Emotional support and love as well as medication and psychological therapy have been proven effective.
One technique for amnesia treatment is cognitive or occupational therapy. In therapy, amnesiacs will develop the memory skills they have and try to regain some they have lost by finding which techniques help retrieve memories or create new retrieval paths. This may also include strategies for organizing information to remember it more easily and for improving understanding of lengthy conversation.[Mayo Clinic Staff (2011) Amnesia: Treatments and Drugs. Mayo Clinic. Retrieved from: http://www.mayoclinic.com/health/amnesia/DS01041/DSECTION=treatments-and-drugs.]
Another coping mechanism is taking advantage of technological assistance, such as a personal digital device to keep track of day-to-day tasks. Reminders can be set up for appointments when to take medications, birthdays and other important events. Many pictures can also be stored to help amnesiacs remember names of friends, family, and co-workers. Notebooks, wall calendars, pill reminder
A pill reminder is any device that reminds users to take medications. Traditional pill reminders are pill containers with electric timers attached, which can be preset for certain times of the day to set off an alarm. More sophisticated pill re ...
s and photographs of people and places are low-tech memory aids that can help as well.
While there are no medications available to treat amnesia, underlying medical conditions can be treated to improve memory. Such conditions include but are not limited to low thyroid function, liver
The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...
or kidney disease
Kidney disease, or renal disease, technically referred to as nephropathy, is damage to or disease of a kidney. Nephritis is an inflammatory kidney disease and has several types according to the location of the inflammation. Inflammation can ...
, stroke
A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
, depression, bipolar disorder
Bipolar disorder, previously known as manic depression, is a mental disorder characterized by periods of depression and periods of abnormally elevated mood that last from days to weeks each. If the elevated mood is severe or associated with ...
and blood clot
A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of c ...
s in the brain. Wernicke–Korsakoff syndrome
Wernicke–Korsakoff syndrome (WKS) is the combined presence of Wernicke encephalopathy (WE) and Korsakoff syndrome. Due to the close relationship between these two disorders, people with either are usually diagnosed with WKS as a single syndrome ...
involves a lack of thiamin
Thiamine, also known as thiamin and vitamin B1, is a vitamin, an essential micronutrient, that cannot be made in the body. It is found in food and commercially synthesized to be a dietary supplement or medication. Phosphorylated forms of thia ...
and replacing this vitamin by consuming thiamin-rich foods such as whole-grain cereals, legumes (beans and lentils), nuts, lean pork, and yeast. Treating alcoholism and preventing alcohol and illicit drug use can prevent further damage, but in most cases will not recover lost memory.
Although improvements occur when patients receive certain treatments, there is still no actual cure remedy for amnesia so far. To what extent the patient recovers and how long the amnesia will continue depends on the type and severity of the lesion.
History
French psychologist Theodule-Armand Ribot was among the first scientists to study amnesia. He proposed Ribot's Law
Ribot's law of retrograde amnesia was hypothesized in 1881 by Théodule Ribot. It states that there is a time gradient in retrograde amnesia, so that recent memories are more likely to be lost than the more remote memories. Not all patients with ...
which states that there is a time gradient in retrograde amnesia. The law follows a logical progression of memory loss due to disease. First, a patient loses the recent memories, then personal memories, and finally intellectual memories. He implied that the most recent memories were lost first.
Case studies have played a large role in the discovery of amnesia and the parts of the brain that were affected. The studies gave important insight into how amnesia affects the brain. The studies also gave scientists the resources into improving their knowledge about amnesia and insight into a cure or prevention. There are several extremely important case studies: Henry Molaison, R.B, and G.D.
Henry Molaison
Henry Molaison
Henry Gustav Molaison (February 26, 1926 – December 2, 2008), known widely as H.M., was an American who had a bilateral medial temporal lobe, temporal lobectomy to surgically resect the anterior two thirds of his Hippocampus, hippocampi, p ...
, formerly known as H.M., changed the way people thought of memory. The case was first reported in a paper by William Beecher Scoville and Brenda Milner
Brenda Milner (née Langford; July 15, 1918) is a British-Canadian neuropsychologist who has contributed extensively to the research literature on various topics in the field of clinical neuropsychology. Milner is a professor in the Department ...
in 1957. He was a patient who had severe epilepsy attributed to a bicycle accident at the age of nine. Physicians were unable to control his seizures with drugs, so the neurosurgeon Scoville tried a new approach involving brain surgery. He removed his medial temporal lobe bilaterally by doing a temporal lobectomy. His epilepsy did improve, but Molaison lost the ability to form new long-term memories (anterograde amnesia). He exhibited normal short-term memory ability. If he was given a list of words, he would forget them in about a minute's time. In fact, he would forget that he had even been given a list in the first place. However, H.M.'s working and short-term memory seemed to be intact. He had a normal digit span and could hold a conversation that did not require him to recall past parts of the conversation. Once Molaison stopped thinking about the lists he was unable to recall them again from long-term memory. This gave researchers evidence that short-term and long-term memory are in fact two different processes. Even though he forgot about the lists, he was still able to learn things through his implicit memory
In psychology, implicit memory is one of the two main types of long-term human memory. It is acquired and used unconsciously, and can affect thoughts and behaviours. One of its most common forms is procedural memory, which allows people to perfo ...
. The psychologists would ask him to draw something on a piece of paper, but to look at the paper using a mirror. Though he could never remember ever doing that task, he would improve after doing it over and over again. This showed the psychologists that he was learning and remembering things unconsciously. In some studies it was found that H.M.'s perceptual learning was intact and that his other cognitive skills were working appropriately. It was also found that some people with declarative information amnesia are able to be primed.
Studies were completed consistently throughout Molaison's lifetime to discover more about amnesia. Researchers did a 14-year follow-up study on Molaison. They studied him for a period of two weeks to learn more about his amnesia. After 14 years, Molaison still could not recall things that had happened since his surgery. However, he could still remember things that had happened prior to the operation. Researchers also found that, when asked, Molaison could answer questions about national or international events, but he could not remember his own personal memories. After his death Molaison donated his brain to science, where they were able to discover the areas of the brain that had the lesions which caused his amnesia, particularly the medial temporal lobe. This case study provided important insight to the areas of the brain that are affected in anterograde amnesia, as well as how amnesia works. H.M.'s case showed us that memory processes are consolidated into different parts of the brain and that short-term and working memory are not usually impaired in cases of amnesia.
Clive Wearing
Another famous historical case of amnesia was that of Clive Wearing. Clive Wearing was a conductor and musician who contracted herpes simplex virus. This virus affected the hippocampal regions of the brain. Because of this damage, Wearing was unable to remember information for more than a few moments. Wearing's non-declarative memory was still functioning but his declarative memory was impaired. To him, he felt that he had just come to consciousness for the first time every time he was unable to hold on to information. This case also can be used as evidence that there are different memory systems for declarative and non-declarative memory. This case was more evidence that the hippocampus is an important part of the brain in remembering past events and that declarative and non-declarative memories have different processes in different parts of the brain.
Patient R.B.
Patient R.B. was a normally functioning man until the age of 52. At age 50, he had been diagnosed with angina and had surgery for heart problems on two occasions. After an ischemic episode (reduction of blood to the brain) that was caused from a heart bypass surgery, R.B. demonstrated a loss of anterograde memory, but almost no loss of retrograde memory, with the exception of a couple of years before his surgery, and presented no sign of any other cognitive impairment. It wasn't until after his death that researchers had the chance to examine his brain, when they found his lesions were restricted to the CA1 portion of the hippocampus. This case study led to important research involving the role of the hippocampus and the function of memory.
Patient G.D.
Patient G.D. was a white male born in 1940 who served in the Navy. He was diagnosed with chronic kidney failure
Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...
and received hemodialysis
Hemodialysis, also spelled haemodialysis, or simply dialysis, is a process of purifying the blood of a person whose kidneys are not working normally. This type of dialysis achieves the extracorporeal removal of waste products such as creatinin ...
treatment for the rest of his life. In 1983, he went to the hospital for elective parathyroidectomy
Parathyroidectomy is the surgical removal of one or more of the (usually) four parathyroid glands. This procedure is used to remove an adenoma or hyperplasia of these glands when they are producing excessive parathyroid hormone (PTH): hyperparathy ...
. He also had a left thyroid lobectomy because of the severe loss of blood in his left lobe. He began having cardiac problems as a result of the surgery and became very agitated. Even five days after being released from the hospital he was unable to remember what had happened to him. Aside from memory impairment, none of his other cognitive processes seemed to be affected. He did not want to be involved in much research, but through memory tests he took with doctors, they were able to ascertain that his memory problems were present for the next 9.5 years until his death. After he died, his brain was donated to science, photographed, and preserved for future study.
In fiction
Global amnesia is a common motif in fiction despite being extraordinarily rare in reality. In the introduction to his anthology ''The Vintage Book of Amnesia'', Jonathan Lethem
Jonathan Allen Lethem (; born February 19, 1964) is an American novelist, essayist, and short story writer. His first novel, ''Gun, with Occasional Music'', a genre work that mixed elements of science fiction and detective fiction, was publishe ...
writes:
Lethem traces the roots of literary amnesia to Franz Kafka
Franz Kafka (3 July 1883 – 3 June 1924) was a German-speaking Bohemian novelist and short-story writer, widely regarded as one of the major figures of 20th-century literature. His work fuses elements of realism and the fantastic. It ...
and Samuel Beckett
Samuel Barclay Beckett (; 13 April 1906 – 22 December 1989) was an Irish novelist, dramatist, short story writer, theatre director, poet, and literary translator. His literary and theatrical work features bleak, impersonal and tragicomic expe ...
, among others, fueled in large part by the seeping into popular culture of the work of Sigmund Freud
Sigmund Freud ( , ; born Sigismund Schlomo Freud; 6 May 1856 – 23 September 1939) was an Austrian neurologist and the founder of psychoanalysis, a clinical method for evaluating and treating psychopathology, pathologies explained as originatin ...
, which also strongly influenced genre films such as ''film noir
Film noir (; ) is a cinematic term used primarily to describe stylish Hollywood crime dramas, particularly those that emphasize cynical attitudes and motivations. The 1940s and 1950s are generally regarded as the "classic period" of American ' ...
''. Amnesia is so often used as a plot device in films, that a widely recognized stereotypical dialogue has even developed around it, with the victim melodramatically asking "Where am I? Who am I? What am I?", or sometimes inquiring of their own name, "Bill? Who's Bill?"[
In movies and television, particularly ]sitcom
A sitcom, a portmanteau of situation comedy, or situational comedy, is a genre of comedy centered on a fixed set of characters who mostly carry over from episode to episode. Sitcoms can be contrasted with sketch comedy, where a troupe may use ne ...
s and soap opera
A soap opera, or ''soap'' for short, is a typically long-running radio or television serial, frequently characterized by melodrama, ensemble casts, and sentimentality. The term "soap opera" originated from radio dramas originally being sponsored ...
s, it is often depicted that a second blow to the head, similar to the first one which caused the amnesia, will then cure it. In reality, however, repeat concussion
A concussion, also known as a mild traumatic brain injury (mTBI), is a head injury that temporarily affects brain functioning. Symptoms may include loss of consciousness (LOC); memory loss; headaches; difficulty with thinking, concentration, ...
s may cause cumulative deficits including cognitive
Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
problems, and in extremely rare cases may even cause deadly swelling of the brain associated with second-impact syndrome
Second-impact syndrome (SIS) occurs when the brain swells rapidly, and catastrophically, after a person has a second concussion before symptoms from an earlier one have subsided. This second blow may occur minutes, days, or weeks after an initial ...
.
In science fiction involving a masquerade
Masquerade or Masquerader may refer to:
Events
* Masquerade ball, a costumed dance event
* Masquerade ceremony, a rite or cultural event in many parts of the world, especially the Caribbean and Africa
* Masqueraders, the performers in the West ...
that hides magical or alien societies from humanity, such as Men in Black
In popular culture and UFO conspiracy theories, men in black (MIB) are purported men dressed in black suits who claim to be quasi-government agents, who harass, threaten, or sometimes even assassinate unidentified flying object (UFO) witnesses t ...
or the SCP Foundation
The SCP Foundation is a fictional secret organization documented by the collaborative-writing wiki project of the same name. Within the website's shared universe, the Foundation is responsible for capturing, containing, and studying various p ...
, fictional organizations can induce deliberate amnesia via drugs or advanced technology to wipe the minds of those that view supernatural phenomena.
See also
References
External links
{{Authority control
Cognitive disorders
Memory disorders