UC San Diego

It is widely accepted that the medial temporal lobe (MTL) and related structures in the diencephalon play a critical role in declarative memory, which is conscious knowledge about facts and events. A fundamental question is whether there are divisions of labor of declarative memory function within the MTL or diencephalon. In one view, specific declarative memory functions (e.g., recognition memory for items) depend on some regions of the MTL and diencephalon but are entirely independent of other regions. In another view, each region of the MTL and diencephalon is important for all declarative memory functions. To address this issue, we assessed the location and extent of brain damage in memory-impaired patients using post-mortem histology and compared the effects of lesions to the MTL or diencephalon on memory performance. Next, we assessed the location and extent of brain damage in living, memory-impaired patients using structural MRI and administered memory tests to patients with damage limited to the hippocampal region. Finally, we used functional neuroimaging to study brain activity in healthy participants performing recognition memory tasks. We report that damage to the MTL or diencephalon produces a common amnesic syndrome with impaired declarative memory (anterograde and retrograde memory) but sparing of nondeclarative memory and other cognitive functions. Further, we report that proposed dichotomies between item memory and associative memory or item memory and source memory do not capture the division of labor of declarative memory function in the MTL and diencephalon. Our findings suggest that each region of the MTL and related regions of the diencephalon play an important role in all declarative memory functions