Neuronal responses at the sight of objects in monkey basal forebrain subregions during operant visual tasks.

The basal forebrain appears to be important in cognitive function. It has been suggested that this region is composed of several cholinergic cell groups, mainly the medial septum, the diagonal band of Broca, and the nucleus basalis of Meynert. To elucidate the functional differences between these subregions, we have recorded single-unit activity from the periventricular areas involving the medial septum, the diagonal band of Broca (ms/dbB), and the substantia innominata (SI), including the nucleus basalis of Meynert, of an object-discriminating monkey. Of 226 ms/dbB and 439 SI neurons analyzed, 36 (15.9%) and 115 (26.2%), respectively, responded to the sight of some complex object. Thirteen (5.8%) ms/dbB and 80 (18.2%) SI neurons responded to virtually all objects and the ratio of these neurons in the SI was higher than that in the ms/dbB. The other 23 (10.2%) ms/dbB and 35 (8.0%) SI neurons responded preferentially to one or two of three categories (rewarding, aversive, or meaningless) of familiar or to unfamiliar objects, and response selectivity to one category of the ms/dbB neurons (15; 6.6%) was higher than that to the SI neurons (14; 3.2%). The results suggest that the SI, including the nucleus basalis of Meynert, may encode visual information about objects more broadly and participate more fully in visual attention than the ms/dbB region, which may be more closely related to learning.