Feedback Regulation of Cholinergic Modulation and Hippocampal Memory Function

Abstract

Models of hippocampal function often focus on the possible autoassociative memory function of region CA3 [Marr, 1971; McNaughton and Morris, 1987; McClelland et al., 1992; Levy, 1989; Eichenbaum and Buckingham, 1990] and the possible heteroassociative memory function of the Schaffer collaterals from region CA3 to region CAI [Levy, 1989; Eichenbaum and Buckingham, 1990; McNaughton, 1991]. However, these models have not accounted for the fact that associative memory models require very different activation dynamics during learning versus recall. To prevent recall of previously learned associations from interfering with the learning of new associations, modifiable synapses must not be the predominant influence on post-synaptic activity during learning. In many models of associative memory function, the associations being stored in the network are clamped during learning (Kohonen, 1984; Anderson, 1983; Hopfield, 1984; Amit, 1988) to prevent the spread of activity across previously modified synapses.