Transsynaptic Mechanisms Controlling Cholinergic Neuronal Activation in the Septohippocampal and nBM-Cortical Pathways: Differential Roles in Memory and Attentional Processes?

Evidence that the nucleus basalis magnocellularis (nBM)-cortical and septohippocampal cholinergic pathways, deriving from the magnocellular forebrain cholinergic complex, are implicated in attention andJor memorization processes has been provided by pharmacological, clinical, and lesion studies (Collerton 1986; Hagan and Morris 1988; Sarter and Bruno 1997a). Based on an outline of these hypotheses, studies comparing changes in the activ ity of these cholinergic pathways induced by learning and memory testing will be described. Results support the concept of differential activation of these pathways as a function of the type (working vs. reference) of memory taxed, the degree of task mastery, and the length of retention required, and they show that the distinct topographic components of the magnocellular forebrain cholinergic complex undergo differential transsynaptic regulation by afferent inputs. In a second section, attempts to identify the neuro-transmitters involved in transsynaptic control over basal activity and the distinct phases of memory-test-induced cholinergic activation are presented. The aim is to provide a framework for conceptualizing the transsynaptic mechanisms that underlie the postulate of differential functional roles for the septohippocampal and nBM-cortical pathways in memorization and attentional processes, and to provide a schema concerning the roles of these pathways in temporary as opposed to long-term memory storage.