The medial temporal lobe and declarative memory
The hippocampus is part of a system of anatomically related structures in the medial temporal lobe that supports the capacity for conscious recollection (declarative memory). In three studies, we investigated memory functions in amnesic patients with bilateral damage limited primarily to the hippocampal region and in other patients with larger lesions of the medial temporal lobe. The results support three conclusions about the neurological organization of human memory. First, to a limited degree, nondeclarative memory can substitute for declarative memory, but what is learned and stored in memory is substantially different depending on which memory system is used. Second, damage limited primarily to the hippocampal region impairs the learning of new facts (semantic memory), just as such damage impairs the learning of new events (episodic memory). Remote memory for factual knowledge is spared. Third, damage to the medial temporal lobe spares remote memory for autobiographical events (episodic memory).