Episodic memory

It has been suggested that this article or section be merged with [[::Autobiographical memory|Autobiographical memory]]. (Discuss)

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Episodic memory, or autobiographical memory, a sub-category of declarative memory, is the recollection of events. It includes time, place, and associated emotions (which affect the quality of the memorization). Episodic memory contrasts and interacts with semantic memory, the memory of facts and concepts. Episodic memories can be likened to written stories.

The cognitive neuroscience of episodic memory

Main article: Episodic memory: Neurological basis

The formation of new episodic memories requires the hippocampus. Without a hippocampus, one is able to form new procedural memories (such as playing the piano) but cannot remember the events during which they happened. See The hippocampus and memory.

The relationship of episodic memory to semantic memory

Episodic memory is thought of as being a "one-shot" learning mechanism. You only need one exposure to an episode to remember it. Semantic memory, on the other hand, can take into consideration multiple exposures to each referent - the semantic representation is updated on each exposure.

Episodic memory can be thought of as a "map" that ties together items in semantic memory. For example, semantic memory will tell you what your dog looks and sounds like. All episodic memories concerning your dog will reference this single semantic representation of "dog" and, likewise, all new experiences with your dog will modify your single semantic representation of your dog.

Some researchers believe that episodic memories are refined into semantic memories over time. In this process, most of the episodic information about a particular event is generalized and the context of the specific events is lost. One modification of this view is that episodic memories which are recalled often are remembered as a kind of monologue. If you tell and re-tell a story repeatedly, you may feel that you no longer remember the event, but that what you're recalling is a kind of pre-written story.

Others believe that you always remember episodic memories as episodic memories. Of course, episodic memories do inform semantic knowledge and episodic memories are reliant upon semantic knowledge. The point is that some people do not believe that all episodic memories will inevitably distill away into semantic memory.

Sex differences in episodic memory performance

According to Brain activation during episodic memory retrieval: sex differences, women tend to outperform men on episodic memory tasks.

Age differences in episodic memory performance

Activation of specific brain areas (mostly the hippocampus) seems to be different between young and older people upon episodic memory retrieval, as shown by Maguire and Frith 2003. Older people tend to activate both left and right hippocampus, while young people activate only the left one.

Episodic memory damage

• The label "Amnesia" is most often given to patients with deficits in episodic memory.
• Alzheimer's Disease tends to damage the hippocampus before other brain areas. This means that AD patients are often classed as amnesiacs.
• A rare type of shell-fish poisoning called "Amnesiac Shellfish Poisoning" (ASP) quite effectively and irreversibly damages the hippocampus, rendering one amnesiac.
• Korsakoff's syndrome is brought on by many years' worth of excessive drinking. The syndrome is not the result of the alcohol, per se; rather, it is caused by the malnutrition that occurs when someone gets a large amount of his calories from alcohol.

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 behavioural indicators of conscious experience (Griffiths et al., 1999).

Clayton & Dickinson (1998) were the first to provide evidence that animals may posess 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 behavioural 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.

Key texts

Books

• Tulving, E. (1983). Elements of Episodic Memory. Oxford: Clarendon Press.

Papers

• Tulving, E. (2001). The origin of autonoesis in episodic memory. In H. L. Roediger, J. S. Nairne, I. Neath, & A. M. Suprenant (Eds.), The nature of remembering: Essays in honor of Robert G. Crowder(pp. 17-34). Washington, D.C.: American Psychological Association.
• Tulving, E. (1999). On the uniqueness of episodic memory. In L.-G. Nilsson & H. J. Markowitsch (Eds), Cognitive neuroscience of memory(pp. 11-42). Gottingen: Hogrefe & Huber.
• Tulving, E. (1992). Episodic memory. In L. Squire (Ed.), Encyclopedia of Learning and Memory(pp. 161-163). New York: Macmillan.
• Tulving, E. (1990). Episodic memory. In M. W. Eysenck (Ed.), The Blackwell Dictionary of Cognitive Psychology(pp. 137-139). Oxford: Blackwell.
• Tulving, E. (1972). Episodic and semantic memory. In E. Tulving and W. Donaldson (Eds.), Organization of Memory (pp. 381-403). New York: Academic Press.
• Tulving, E. (1993). What is episodic memory? Current Perspectives in Psychological Science, 2, 67-70.
• Tulving, E. (1986a). Episodic and semantic memory: Where should we go from here? Behavioral and Brain Sciences, 9, 573-577.
• Tulving, E. (1986b). What kind of a hypothesis is the distinction between episodic and semantic memory? Journal of Experimental Psychology Learning, Memory, and Cognition, 12, 307-311.
• [[Tulving, E. (1983b). Ecphoric processes in episodic memory. Philosophical Transactions of the Royal Society, London, B302, 361-371.

Additional material

Papers

• Google Scholar
• Deisseroth K., Singla S., Toda H., Monje M., Palmer T.D., Malenka R.C. (2004) Excitation-neurogenesis coupling in adult neural stem/progenitor cells. Neuron. 2004 May 27;42(4):535-52.
• Griffiths, D. P., Dickinson, A. & Clayton, N. S. (1999). Declarative and episodic memory: What can animals remember about their past? Trends in Cognitive Science, 3, 74–80.
• Clayton, N. S. & Dickinson, A. (1998). Episodic-like memory during cache recovery by scrub-jays. Nature, 395, 272-274.

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