Cerebral Memory Circuits

This chapter focuses on how the primate forebrain might be organized at the systems level to yield both stimulus memmy (i.e., recognition and recall) and habit formation (i.e., stimulus-response [S-R] learning). Derived mainly from studies in monkeys, the following hypotheses are proposed: (a) stimulus recognition depends on the fonnation of a Hebbian 'cell assembly' in a c:ortical sensory processing pathway; the cells are 'assembled' by action of a feedback circuit running from the sensmy pathway, through limbic structures, to chemical neuromodulatory systems (e.g., cholinergic, noradrenergic, serotonergic), and then back to the limbic structures and the sensory pathway; (b) stimulus recall depends on the formation of a Hebbian 'phase sequence,' consisting of one cell assembly linked to another via limbic structures, by action of the same feedback circuit as outlined above; (c) S-R learning depends on linking a c:ortically processed sensory input to an extrapyramidally generated motor output through the fee pack action of chemical neuromodulatory (e.g., dopaminergic) systems on sensory-neostriata( connections. Each of these hypotheses is elaborated and its psychological implications discussed.