What is episodic memory?
Episodic memory, or autobiographical memory, is the explicit memory of events (e.g. remembering the last wedding you went to). 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 have some similarities to written stories.
The cognitive neuroscience of episodic memory
The formation of new episodic memories requires the hippocampus. If someone cuts out both your hippocampi then you wont ever be able to form new episodic memories. You'll be able to form new procedural memories (such as playing the piano) but you'll never remember the events during which you learnt the piano. See the excellent section on memory and the hippocampus.
Does the hippocampus store episodic memories for life?
Researchers argue over how long episodic memories are stored in the hippocampus. Some researchers believe that episodic memories are always reliant on the hippocampus - even memories from way back in your past. 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 ). If the hippocampus is deliberately deleting old memories then old memories must be stored somewhere else.
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 (which is lucky, seeing as real-life episodes only happen once!). 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. If you consider the episodic memory trace to be like a written story then semantic memory could be thought of as the knowledge of what the characters look like and general knowledge of the environment. For example, semantic memory will tell you what your dog looks and sounds like and that dogs like to chase sticks. All episodic memories concerning your dog will reference this single semantic representation of "dog" and, like wise, 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've ever had to tell and re-tell a story until you're sick to death of the story then you may have experienced the sensation that you no longer remember the event, 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. But beware of seeing too much meaning in a single study.
When episodic memory stops working
- 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 type of shell-fish poisoning called "Amesic Shellfish Poisoning" or ASP quite effectively and irreversibly damages your hippocampi, rendering you amnesic. But don't worry shellfish lovers, ASP is very rare.
- Korsakoff's syndrome is brought on by many year's worth of excessive drinking or malnutrition (or both).