Episodic memory
|
|
Episodic memory, or autobiographical memory, is the explicit memory 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.
| Contents |
The cognitive neuroscience of episodic memory
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 hippocampus's role in memory storage
Researchers do not agree about how long episodic memories are stored in the hippocampus. 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 to the neocortex. The latter view is strengthened by recent evidence that neurogenesis in the adult hippocampus may ease the removal of old memories and increase the efficiency of forming new memories (Deisseroth et al 2004 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15157417&itool=iconabstr)).
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 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11194411), 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 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12805116). 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 amnesics.
- A rare type of shell-fish poisoning called "Amesic Shellfish Poisoning" or ASP quite effectively and irreversibly damages your hippocampus, rendering you amnesic.
- Korsakoff's syndrome is brought on by many year's 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 their calories from alcohol .
Episodic memory in animals
"The problem with defining episodic memory in terms of phenomenological experiences is that it is impossible to demonstrate the presence or absence of episodic memory in animals, because there are no agreed non-linguistic behavioural markers of conscious experience" (de Kort, Dickinson, and Clayton, 2005). A potential solution to this problem is to use Tulving's (1972) conceptualization of episodic memory in terms of its "what, where, when" content. Clayton, Dickinson, and a number of their colleagues have done just this, attempting to test for episodic memory in animals using behavioral markers that satisfy the criteria of a "what, where, when" representation. Thus, any evidence of an analogous mnemonic capability in animals is deemed by them to be "episodic-like memory."
References
- de Kort, D., and Clayton. (2005). Retrospective cognition by food-caching western scrub-jays. Learning & Motivation, 36, 159-176.
- Tulving, E. (1972). Episodic and semantic memory. In E. Tulving & W. Donaldson (Eds.), Organisation of memory (pp. 381–403). New York: Academic Press.