Theories of episodic memory

Theories of episodic memory need to specify the encoding (representing), st orage, and retrieval processes that underlie this form of memory and indica te the brain regions that mediate these processes and how they do so. Repre sentation and re-representation (retrieval) of the spatiotemporally linked series of scenes, which constitute an episode, are probably mediated primar ily by those parts of the posterior neocortex that process perceptual and s emantic information. However, some role of the frontal neocortex and medial temporal lobes in representing aspects of context and high-level visual ob ject information at encoding and retrieval cannot currently be excluded. Ne vertheless, it is widely believed that the frontal neocortex is mainly invo lved in coordinating episodic encoding and retrieval and that the medial te mporal lobe,,, store aspects of episodic information, Establishing where st orage is located is very difficult and disagreement remains about the role of the posterior neocortex in episodic memory storage. One view is that thi s region stores all aspects of episodic memory ab initio for as long as mem ory lasts. This is compatible with evidence that the amygdala, basal forebr ain, and midbrain modulate neocortical storage. Another view is that the po sterior neocortex only gradually develops the ability to store some aspects of episodic information as a function of rehearsal over time and that this information is initially stored by the medial temporal lobes. A third view is that the posterior neocortex never stores these aspects of episodic inf ormation because the medial temporal lobes store them for as long as memory lasts in an increasingly redundant fashion. The last two views both postul ate that the medial temporal lobes initially store contextual markers that serve to cohere featural information stored in the neocortex. Lesion and fu nctional neuroimaging evidence still does not clearly distinguish between t hese views. Whether the feeling that an episodic memory is familiar depends on retrieving an association between a retrieved episode and this feeling, or by an attribution triggered by a printing process, is unclear. Evidence about whether the hippocampus and medial temporal lobe cortices play diffe rent roles in episodic memory is conflicting. Identifying similarities and differences between episodic memory and both semantic memory and priming wi ll require careful componential analysis of episodic memory.