Object memory and perception in the medial temporal lobe: an alternative approach

The medial temporal lobe (MTL) includes several structures--the hippocampus, and the adjacent perirhinal, entorhinal and parahippocampal cortices--that have been associated with memory for at least the past 50 years. These components of the putative 'MTL memory system' are thought to operate together in the service of declarative memory--memory for facts and events--having little or no role in other functions such as perception. Object perception, however, is thought to be independent of the MTL, and instead is usually considered to be the domain of the ventral visual stream (VVS) or 'what' pathway. This 'textbook' view fits squarely into the prevailing paradigm of anatomical modularisation of psychological function in the brain. Recent studies, however, question this view, indicating that first, the MTL is functionally heterogeneous, and second, structures in the MTL might have a role in perception. Furthermore, the specific contributions of the individual structures within the MTL are being elucidated. These new findings indicate that it might no longer be useful to assume a strict functional dissociation between the MTL and the VVS, and that psychological functions might not be modularised in the way usually assumed. We propose an alternative approach to understanding the functions of these brain regions in terms of what computations they perform, and what representations they contain.