Amnesia and the hippocampus

Abstract

Long-term memory impairments have great medical significance and a considerable health and economic burden. Understanding their cognitive and neuroanatomical underpinnings is of crucial importance. Severe amnesia is usually observed following bilateral hippocampal pathology. This review addresses the precise role of the hippocampus and related medial temporal lobe structures in amnesia. Disagreements exist over whether, following selective hippocampal damage: retrograde amnesia for episodic memories is temporally limited or extensive and ungraded; anterograde amnesia involves both recollective and familiarity processes. It is accepted that material specific impairments follow unilateral medial temporal lobe damage, with verbal and nonverbal memory lateralized to left or right, respectively. Memory for unknown faces, however, may not depend on the hippocampus. Pharmacological studies in animals, with some extension to humans, highlight promising future therapeutic interventions targeting synaptic plasticity modulation. Despite considerable progress, some issues remain unresolved. The available evidence favours the view, however, that the hippocampus, in conjunction with other cortical areas, is critical for the retrieval of remote episodic memories and for both recollection and familiarity anterograde memory processes. There are as yet no effective pharmacological treatments for medial temporal lobe amnesia, but various rehabilitative techniques may be useful.