Home      Discussion      Topics      Dictionary      Almanac
Signup       Login
Episodic memory

Episodic memory

Discussion
Ask a question about 'Episodic memory'
Start a new discussion about 'Episodic memory'
Answer questions from other users
Full Discussion Forum
 
Encyclopedia
Episodic memory is the memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....

 of autobiographical events (time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

s, places
Location (geography)
The terms location and place in geography are used to identify a point or an area on the Earth's surface or elsewhere. The term 'location' generally implies a higher degree of can certainty than "place" which often has an ambiguous boundary relying more on human/social attributes of place identity...

, associated emotion
Emotion
Emotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...

s, and other contextual knowledge
Knowledge
Knowledge is a familiarity with someone or something unknown, which can include information, facts, descriptions, or skills acquired through experience or education. It can refer to the theoretical or practical understanding of a subject...

) that can be explicitly stated. Semantic
Semantic memory
Semantic memory refers to the memory of meanings, understandings, and other concept-based knowledge unrelated to specific experiences. The conscious recollection of factual information and general knowledge about the world is generally thought to be independent of context and personal relevance...

 and episodic memory together make up the category of declarative memory
Declarative memory
Declarative memory is one of two types of long term human memory. It refers to memories which can be consciously recalled such as facts and knowledge. Its counterpart is known as non-declarative or Procedural memory, which refers to unconscious memories such as skills...

, which is one of the two major divisions in memory. The counterpart to declarative, or explicit memory, is procedural memory
Procedural memory
Procedural memory is memory for how to do things. Procedural memory guides the processes we perform and most frequently resides below the level of conscious awareness. When needed, procedural memories are automatically retrieved and utilized for the execution of the integrated procedures involved...

, or implicit memory
Implicit memory
Implicit memory is a type of memory in which previous experiences aid in the performance of a task without conscious awareness of these previous experiences. Evidence for implicit memory arises in priming, a process whereby subjects show improved performance on tasks for which they have been...

.

Events that are recorded into episodic memory may trigger episodic learning, i.e. a change in behavior that occurs as a result of an event. For example, a fear of dogs that follows being bitten by a dog is episodic learning.

Cognitive neuroscience


The formation of new episodic memories requires the medial temporal lobe, a structure that includes the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

. Without the medial temporal lobe, one is able to form new procedural memories
Procedural memory
Procedural memory is memory for how to do things. Procedural memory guides the processes we perform and most frequently resides below the level of conscious awareness. When needed, procedural memories are automatically retrieved and utilized for the execution of the integrated procedures involved...

 (such as playing the piano) but cannot remember the events during which they happened (See the hippocampus and memory).

The prefrontal cortex
Prefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...

 (and in particular the left hemisphere) is also involved in the formation of new episodic memories (also known as episodic encoding). Patients with damage to the prefrontal cortex can learn new information, but tend to do so in a disordered fashion. For example, they might show normal recognition of an object they had seen in the past, but fail to recollect
Recollection
Recall in memory refers to the retrieval of events or information from the past. Along with encoding and storage, it is one of the three core processes of memory. There are three main types of recall: free recall, cued recall and serial recall...

 when or where it had been viewed. Some researchers believe that the prefrontal cortex helps organize information for more efficient storage, drawing upon its role in executive function. Others believe that the prefrontal cortex underlies semantic strategies which enhance encoding, such as thinking about the meaning of the study material or rehearsing it in working memory
Working memory
Working memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...

.

The hippocampus's role in memory storage


Researchers do not agree about how long episodic memories are stored in the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

. Some researchers believe that episodic memories always rely on the hippocampus. Others believe the hippocampus only stores episodic memories for a short time, after which the memories are consolidated
Memory consolidation
Memory consolidation is a category of processes that stabilize a memory trace after the initial acquisition. Consolidation is distinguished into two specific processes, synaptic consolidation, which occurs within the first few hours after learning, and system consolidation, where...

 to the neocortex
Neocortex
The neocortex , also called the neopallium and isocortex , is a part of the brain of mammals. It is the outer layer of the cerebral hemispheres, and made up of six layers, labelled I to VI...

. The latter view is strengthened by recent evidence that neurogenesis
Neurogenesis
Neurogenesis is the process by which neurons are generated from neural stem and progenitor cells. Most active during pre-natal development, neurogenesis is responsible for populating the growing brain with neurons. Recently neurogenesis was shown to continue in several small parts of the brain of...

 in the adult hippocampus may ease the removal of old memories and increase the efficiency of forming new memories.

Relationship to semantic memory


Endel Tulving originally described episodic memory as a record of a person’s experience that held temporally dated information and spatio-temporal relations. A feature of episodic memory that Tulving later elaborates on is that it allows an agent to travel back in time. A current situation may cue retrieval of a previous episode, so that context that colors the previous episode is experienced at the immediate moment. The agent is provided with a means of associating previous feelings with current situations. Semantic memory
Semantic memory
Semantic memory refers to the memory of meanings, understandings, and other concept-based knowledge unrelated to specific experiences. The conscious recollection of factual information and general knowledge about the world is generally thought to be independent of context and personal relevance...

,on the other end, is a structured record of facts, concepts and skills that we have acquired. Semantic information is derived from accumulated episodic memory. Episodic memory can be thought of as a "map" that ties together items in semantic memory. For example, all encounters with how a "dog" looks and sounds like will make up the semantic representation of that word. All episodic memories concerning your dog will then reference this single semantic representation of "dog" and, likewise, all new experiences with your dog will modify your single semantic representation of your dog.

Together, semantic and episodic memory make up our declarative memory. They each represent different parts of context to form a complete picture. As such, something that affects episodic memory can also affect semantic memory. For example, anterograde amnesia, from damage of the medial temporal lobe, is an impairment of declarative memory that affects both episodic and semantic memory operations. Originally, Tulving proposed that episodic and semantic memory were separate systems that competed with each other in retrieval. However, this theory was rejected when Howard and Kahana completed experiments on latent semantic analysis (LSA) that supported the opposite. Instead of an increase in semantic similarity when there was a decrease in the strength of temporal associations, the two worked together so semantic cues on retrieval were strongest when episodic cues were strong as well.

Age differences


Activation of specific brain areas (mostly the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

) seems to be different between younger and older people upon episodic memory retrieval. Older people tend to activate both left and right hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

, while younger people activate only the left one. For more information, see aging and memory.

Relationship to emotion


The relationship between emotion and memory
Emotion and memory
Emotion can have a powerful impact on memory. Numerous studies have shown that the most vivid autobiographical memories tend to be of emotional events, which are likely to be recalled more often and with more clarity and detail than neutral events....

 is complex, but generally, emotion tends to increase the likelihood that an event will be remembered later and that it will be remembered vividly. Flashbulb memory
Flashbulb memory
A flashbulb memory is a highly detailed, exceptionally vivid 'snapshot' of the moment and circumstances in which a piece of surprising and consequential news was heard. Flashbulb memory is an appropriate name for the phenomenon in that it suggests surprise, an indiscriminate illumination, and...

 is one example of this.

Pharmacological enhancement


In healthy adults, longterm visual episodic memory can be enhanced specifically through administration of the Acetylcholine esterase inhibitor Donepezil
Donepezil
Donepezil, marketed under the trade name Aricept by its developer Eisai and partner Pfizer, is a centrally acting reversible acetylcholinesterase inhibitor. Its main therapeutic use is in the palliative treatment of mild to moderate Alzheimer's disease. Common side effects include...

, whereas verbal episodic memory can be improved in persons with the val/val genotype of the val158met polymorphism through administration of the CNS penetrant specific catecholamine-O-methyltransferase
Catechol-O-methyl transferase
Catechol-O-methyltransferase is one of several enzymes that degrade catecholamines such as dopamine, epinephrine, and norepinephrine. In humans, catechol-O-methyltransferase protein is encoded by the COMT gene...

 inhibitor Tolcapone
Tolcapone
Tolcapone is a drug that inhibits the enzyme catechol-O-methyl transferase . - Uses :Tolcapone is used in the treatment of Parkinson's disease as an adjunct to levodopa/carbidopa medication.- Chemistry :...

. Furthermore, episodic memory is enhanced through AZD3480 a selective agonist at the neuronal alpha4beta2 nicotinic receptor, which is developed by the company Targacept. Currently, there are several other products developed by several companies—including new catecholamine-O-methyltransferase inhibitors with fewer side effects—that aim for improving episodic memory. A recent placebo controlled study found that DHEA, which is a functional cortisol antagonist, improves episodic memory in healthy young men (Alhaj et al. 2006).

Damage

  • Based on a review of behavioral studies, it is suggested that there may be selective damage to the limbic-prefrontal episodic memory system in some people with autism
    Autism
    Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...

    . Another study points to evidence of autistic deficits in the episodic or self-conscious memory of personally experienced events (Joseph et al., 2003).
  • The label "amnesia
    Amnesia
    Amnesia is a condition in which one's memory is lost. The causes of amnesia have traditionally been divided into categories. Memory appears to be stored in several parts of the limbic system of the brain, and any condition that interferes with the function of this system can cause amnesia...

    " is most often given to patients with deficits in episodic memory.
  • Alzheimer's disease
    Alzheimer's disease
    Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...

     tends to damage the hippocampus
    Hippocampus
    The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

     before other brain
    Human brain
    The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...

     areas. This means that AD patients are often classed as amnesiacs.
  • A rare type of shellfish poisoning called amnesic shellfish poisoning
    Amnesic shellfish poisoning
    Amnesic shellfish poisoning is a human illness caused by consumption of the marine biotoxin called domoic acid. This toxin is produced naturally by marine diatoms belonging to the genus Pseudo-nitzschia and the species...

     or "ASP" quite effectively and irreversibly damages the hippocampus, rendering one amnesic.
  • Korsakoff's syndrome
    Korsakoff's syndrome
    Korsakoff's syndrome is a neurological disorder caused by the lack of thiamine in the brain. Its onset is linked to chronic alcohol abuse and/or severe malnutrition...

     is caused by thiamine
    Thiamine
    Thiamine or thiamin or vitamin B1 , named as the "thio-vitamine" is a water-soluble vitamin of the B complex. First named aneurin for the detrimental neurological effects if not present in the diet, it was eventually assigned the generic descriptor name vitamin B1. Its phosphate derivatives are...

     (vitamin B1) deficiency, a form of malnutrition
    Malnutrition
    Malnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....

     which can be precipitated by overconsumption of alcoholic beverage
    Alcoholic beverage
    An alcoholic beverage is a drink containing ethanol, commonly known as alcohol. Alcoholic beverages are divided into three general classes: beers, wines, and spirits. They are legally consumed in most countries, and over 100 countries have laws regulating their production, sale, and consumption...

    s compared to other foods.
  • An acute cortisol
    Cortisol
    Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...

     level (by injection) has been found to significantly inhibit the recall
    Recall (memory)
    Recall in memory refers to the retrieval of events or information from the past. Along with encoding and storage, it is one of the three core processes of memory. There are three main types of recall: free recall, cued recall and serial recall...

     of autobiographical memories which may contribute to memory deficits found in depression.
  • The use of some illicit drugs such as MDMA ("Ecstasy") has been associated with persistent deficits in episodic memory.

In animals


In 1997, there was little evidence for episodic memory outside of humans. This is probably due to the difficulty in testing for it in animals. To meet the criteria of episodic memory, as espoused by Tulving (1983), evidence of conscious recollection must be provided. But demonstrating episodic memory in the absence of language, and therefore in non-human animals, is impossible because there are no agreed non-linguistic behavioral indicators of conscious experience (Griffiths et al., 1999).

Clayton & Dickinson (1998) were the first to provide evidence that animals may possess episodic memory. They demonstrated that Western scrub-jays (Aphelocoma californica) remember where they cached different food types and discriminately recovered them, depending on the perishability of the item and the amount of time that elapsed since caching. Thus, scrub-jays appear to remember the "what-where-and-when" of specific caching events in the past. Clayton & Dickinson (1998) argued that such performance met the behavioral criteria for episodic memory. However, because the study did not address the phenomenological aspects of episodic memory, the authors referred to this ability as "episodic-like" memory.

According to a study done by the University of Edinburgh in 2006, hummingbirds are the first animal to demonstrate two aspects of episodic memory—the ability to recall where certain flowers were located and how recently they were visited. Scientists tracked how often hummingbirds visited eight artificial flowers filled with a sucrose solution in the birds' feeding grounds. They refilled half the flowers at 10 minute intervals and the other half 20 minutes after they had been emptied. The birds' return to the flowers matched the refill schedules: flowers refilled at 10-minute intervals were visited sooner. "To our knowledge, this is the first demonstration that animals in the wild can remember both the locations of food sources and when they visited them," said Susan Healy, of the University of Edinburgh.

Other studies have demonstrated this episodic-like memory in other animal species, which have brains more similar to humans. For example, Kart-Teke and colleagues have demonstrated rats' preference for items it sees which is dependent on what it saw, where it saw it and when it saw it (Kart-Teke et al., 2006). In addition, studies by Eacott and colleagues (Eacott et al., 2005) have shown rats can recall (remember without any cueing influences) what they saw and where depending on which past situation they are being asked to remember.

Nonetheless, some scholars remain cautious about comparisons to human episodic memory (Suddendorf & Busby, 2003). Purported episodic-like memory often seems fixed to a particular domain or could be explained in terms of procedural or semantic memory. The problem may be better tractable by studying episodic memory's adaptive counterpart: the capacity to flexibly imagine future events. Suddendorf (2006) argues that the emergence of the human capacity to travel mentally to past and future events may have been a prime mover in hominin evolution.

A recent experiment addressed one of Suddendorf and Busby (2003)'s specific criticisms (the Bischof-Köhler hypothesis, which states that nonhuman animals can only take actions based on immediate needs, as opposed to future needs). Correia and colleagues demonstrated that Western scrub-jays can selectively cache different types of foods depending on which type of food they will desire at a future time, offering strong evidence against the Bischof-Köhler hypothesis by demonstrating that scrub-jays can flexibly adjust their behavior based on past experience of desiring a particular food.

Autobiographical memory


An autobiographical memory
Autobiographical memory
Autobiographical memory is a memory system consisting of episodes recollected from an individual's life, based on a combination of episodic and semantic memory.-Formation:Conway and Pleydell-Pearce proposed that autobiographical...

is a personal representation of general or specific events and personal facts. Autobiographical memory also refers to memory of a person's history. An individual does not remember exactly everything that has happened in one's past. Memory is constructive, where previous experience affects how we remember events and what we end up recalling from memory. Autobiographical memory is constructive and reconstructed as an evolving process of past history. A person's autobiographical memory is fairly reliable; although, the reliability of autobiographical memories is questionable because of memory distortions.

Autobiographical memories can differ for special periods of life. People recall few personal events from the first years of their lives. The loss of these first events is called childhood or infantile amnesia. People tend to recall many personal events from adolescence and early adulthood. This effect is called the reminiscence bump
Reminiscence bump
The reminiscence bump is the tendency for older adults to have increased recollection for events that occurred during their adolescence and early adulthood...

. Finally, people recall many personal events from the last few years. This is called the recency effect. For adolescents and young adults the reminiscence bump and the recency effect coincide.

It is known that autobiographical memories initially are stored as episodic memories, but it is currently unknown if autobiographical memories are the same as episodic memories or if the autobiographical memories become converted to semantic memories
Semantic memory
Semantic memory refers to the memory of meanings, understandings, and other concept-based knowledge unrelated to specific experiences. The conscious recollection of factual information and general knowledge about the world is generally thought to be independent of context and personal relevance...

 with time.

Types

  • Specific Events
    • When you first stepped foot in the ocean
      Ocean
      An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

      .
  • General Events
    • What it feels like stepping into the ocean in general. This is a memory of what a personal event is generally like. It might be based on the memories of having stepped in the ocean, many times during the years.
  • Personal Facts
    • "Who was the Prime Minister of Italy
      Prime minister of Italy
      The Prime Minister of Italy is the head of government of the Italian Republic...

       when I was born?"
  • Flashbulb Memories
    • Flashbulb memories
      Flashbulb memory
      A flashbulb memory is a highly detailed, exceptionally vivid 'snapshot' of the moment and circumstances in which a piece of surprising and consequential news was heard. Flashbulb memory is an appropriate name for the phenomenon in that it suggests surprise, an indiscriminate illumination, and...

       are critical autobiographical memories about a major event. Some flashbulb memories are shared within a social group:
"The assassination of John Kennedy
John F. Kennedy
John Fitzgerald "Jack" Kennedy , often referred to by his initials JFK, was the 35th President of the United States, serving from 1961 until his assassination in 1963....

?"
"The assassination of Martin Luther King, Jr.
Martin Luther King, Jr.
Martin Luther King, Jr. was an American clergyman, activist, and prominent leader in the African-American Civil Rights Movement. He is best known for being an iconic figure in the advancement of civil rights in the United States and around the world, using nonviolent methods following the...

?"
"The Challenger explosion
STS-51-L
STS-51-L was the twenty-fifth flight of the American Space Shuttle program, which marked the first time an ordinary civilian, schoolteacher Christa McAuliffe, had flown aboard the Space Shuttle. The mission used Space Shuttle Challenger, which lifted off from the Launch Complex 39-B on 28 January...

?"
"The verdict in the O.J. Simpson trial?"
"When you learned that Princess Diana had died?"
"When you heard about 9/11?"

Neural network models


Episodic memories can be stored in autoassociative neural networks (e.g.,a Hopfield network) if the stored representation includes information on the spatiotemporal context in which an item was studied.

External links