Systematic regional differences in the cholinergic innervation of the primate cerebral cortex: distribution of enzyme activities and some behavioral implications.

Choline acetyltransferase and acetylcholinesterase enzymatic activities were measured in 33 cytoarchitectonic subregions of the cerebral cortex in two rhesus monkeys. As expected, the hippocampus and amygdala were rich in these enzymes. In addition, the paralimbic (mesocortical) regions of the brain (e.g., parahippocampal, insular, caudal orbitofrontal, and temporopolar areas) also contained high levels of both enzymes. In contrast, the concentration of these cholinergic markers was the lowest within all frontal and temporoparietal association areas. As a group, the primary sensory and motor regions contained an intermediate level of choline acetyltransferase activity. Both cholinergic markers also showed a gradual increase from the isocortical toward the more primitive periallocortical subsectors of paralimbic areas. These anatomical patterns have potential implications for the role of cholinergic pathways in the memory process and in the pathogenesis of Alzheimer's disease.