Memory and forgetting: long-term and gradual changes in memory storage.

Behavioral forgetting can reflect, in part, a literal loss of information from storage and a corresponding loss of some of the synaptic changes that initially represented the stored information. Coordinated neural activity in the neocortex is thought to underlie perception and the capacity for immediate memory. Simultaneous and coordinated activity in the neocortex is sufficient for the task of perception and short-term memory. The sites of storage in the neocortex undergo two, possibly related, kinds of changes. First, forgetting occurs because of the establishment of new connections, which interfere with the coherence of already established networks and because of actual weakening or loss of existing connections within established networks. Second, the distributed networks that together constitute a whole memory develop greater coherence, perhaps by developing functional corticocortical connections or by rerepresenting information in a more efficient form. Because of these gradual changes, remembering becomes possible without the participation of the medial temporal lobe memory system.