The cholinergic contribution to neuromodulation in the cerebral cortex

The cerebral cortex of the human brain receives an intense cholinergic innervation from the nucleus basalis of Meynert. This nucleus is very highly developed and quite heterogeneous in composition. The cholinergic contingent of neurons associated with the nucleus basalis is designated the Ch4 cell group. The Ch4 cell group has topographically organized cortical projections which are directed to all parts of the cerebral cortex, but particularly to the limbic cortex and the amygdala. The organization of this projection suggests that it may play a critical role in enhancing the neural encoding of behaviorally relevant events by the appropriate cortical neurons. The cortical cholinergic projection from Ch4 is a principal component of the ascending reticular activating system.