THE CRITICAL ROLE OF CHOLINERGIC BASAL FOREBRAIN NEURONS IN MORPHOLOGICAL CHANGE AND MEMORY ENCODING - A HYPOTHESIS

It has been known for a long time that cholinergic basal forebrain neu rons which project to the cerebral cortex play a role in learning and memory. Behavioral studies following lesions, for example, repeatedly have suggested multiple learning-related roles for these neurons. Apar t from behavioral studies, cholinergic neurons have been shown to poss ess extraordinarily plastic axons. This plasticity has not been relate d comprehensively to mnemonic devises, even though morphological chang es in the CNS are prime candidates for the neural engram. In this pape r, I propose a hyothesis that relates these two characteristics of cho linergic neurons. This hypothesis is that plastic cholinergic axon ter minals induce structural reorganization in their targets during memory storage. Possible intracellular mechanisms are examined, whereby acet ylcholine release in the cerebral cortex could cause postsynaptic stru ctural changes. Finally, the characteristics of the overall cholinergi c - cholinoceptive cell ''engram'' are elaborated with particular atte ntion paid to the encoding of tile stimulus properties along with the context and meaning of the stimulus. (C) 1996 Academic Press, Inc.