Attentional functions of cortical cholinergic inputs: what does it mean for learning and memory?

The hypothesis that cortical cholinergic inputs mediate attentional functions and capacities has been extensively substantiated by experiments assessing the attentional effects of specific cholinotoxic lesions of cortical cholinergic inputs, attentional performance-associated cortical acetylcholine release, and the effects of pharmacological manipulations of the excitability of basal forebrain corticopetal cholinergic projections on attentional performance. At the same time, numerous animal experiments have suggested that the integrity of cortical cholinergic inputs is not necessary for learning and memory, and a dissociation between the role of the cortical cholinergic input system in attentional functions and in learning and memory has been proposed. We speculate that this dissociation is due, at least in part, to the use of standard animal behavioral tests for the assessment of learning and memory which do not sufficiently tax defined attentional functions. Attentional processes and the allocation of attentional capacities would be expected to influence the efficacy of the acquisition and recall of declarative information and therefore, persistent abnormalities in the regulation of the cortical cholinergic input system may yield escalating impairments in learning and memory. Furthermore, the cognitive effects of loss of cortical cholinergic inputs are augmented by the disruption of the top-down regulation of attentional functions that normally acts to optimize information processing in posterior cortical areas. Because cortical cholinergic inputs play an integral role in the mediation of attentional processing, the activity of cortical cholinergic inputs is hypothesized to also determine the efficacy of learning and memory.