Images of medial temporal lobe functions in human learning and memory

Investigations of the neural basis of mammalian memory have focused more often on the medial temporal lobe (MTL) than on any other brain region. In humans, the amnesic syndrome revealed the essential importance of the multiple structures located in the MTL system for declarative memory (the remembrance of events and facts). Other neural systems mediate procedural forms of memory, including delay eyeblink conditioning, which depends on the cerebellum, and cognitive skill learning, which depends on the striatum. We review three functional imaging studies that reveal different patterns of MTL activation associated with declarative and procedural memory tasks. One study shows separate MTL activations during the encoding or retrieval of declarative memories. A second study shows MTL activation that occurs in parallel with cerebellum-dependent delay eyeblink conditioning, but does not appear to influence that form of procedural memory. A third study reveals suppression of the MTL during striatum-dependent cognitive skill learning. These studies provide images of MTL activations that are correlated with, independent from, or antagonistic to memory performance.