CENTRAL CHOLINERGIC SYSTEMS AND COGNITION

The organization and possible functions of basal forebrain and pontine cholinergic systems are reviewed. Whereas the basal forebrain choline rgic neuronal projections likely subserve a common electrophysiologica l function, e.g. to boost signal-to-noise ratios in cortical target ar eas, this function has different effects on psychological processes de pendent upon the neural network operations within these various cortic al domains. Evidence is presented that (a) the nucleus basalis-neocort ical cholinergic system contributes greatly to visual attentional func tion, but not to mnemonic processes per se; (b) the septohippocampal p rojection is involved in the modulation of short-term spatial (working ) memory processes, perhaps by prolonging the neural representation of external stimuli within the hippocampus; and (c) the diagonal band-ci ngulate cortex cholinergic projection impacts on the ability to utiliz e response rules through conditional discrimination. We also suggest t hat nucleus basalis-amygdala cholinergic projections have a role in th e retention of affective conditioning while brainstem cholinergic proj ections to the thalamus and midbrain dopamine neurons affect basic aro usal processes (e.g. sleep-wake cycle) and behavioral activation, resp ectively. The possibilities and limitations of therapeutic interventio ns with procholinergic drugs in patients with Alzheimer's disease and other neurodegenerative disorders in which basal forebrain cholinergic neurons degenerate are also discussed.