SPATIAL, BEHAVIORAL AND SENSORY CORRELATES OF HIPPOCAMPAL CA1 COMPLEXSPIKE CELL-ACTIVITY - IMPLICATIONS FOR INFORMATION-PROCESSING FUNCTIONS

The aim of this review is to better understand hippocampal function dr awing almost entirely from single unit recording studies of pyramidal cells in areas CA1 and CA3 of behaving animals. Hippocampal location-s electivity (''place cell activity'') as well as place-independent beha vioral correlates and sensory-triggered discharges are demonstrated to have common features: (1) abstraction, that is, development within th e hippocampal circuit of novel, cue-invariant supramodal representatio ns; (2) varying degrees of generalization or specificity; (3) capacity for abrupt changes in discharge correlates of individual neurons as t he animal changes its behavior pattern or its environment changes dram atically; (4) though individual neurons discharge when the subject occ upies a certain place, or performs a certain behavior, the ensemble of hippocampal neurons comprehensively represent the whole environment a nd all behaviors required for the task at hand. A concordance is propo sed: hippocampal neuronal discharge correlates represent elements part itioned from information abstracted along one or more systems of categ orization or ''information domains'': the physical structure of the en vironment, regularities in the behavioral exigencies of the current si tuation. (Sensory stimuli can be considered as temporally varying feat ures of the environment.) Location-selectivity and behavioral correlat es are extreme cases, and mixed correlates occur. The hippocampus is p roposed to carry out several fundamental processes that transform info rmation: abstraction, partitioning and recombination, that is, formati on of conjunctive associations between events. Simultaneously activate d neurons could then promote extrahippocampal associations linking tog ether the diverse brain regions at the origin of these signals. Copyri ght (C) 1996 Elsevier Science Ltd.