The primate nucleus basalis of Meynert: neuronal activity related to a visuomotor tracking task

The activity of neurons in the nucleus basalis of Meynert (nbM), both the compact (nbMc) and interstitial (nbMi) components, has been examined in monkeys trained to perform a visuomotor step-tracking task. This study was carried out in the same animals and with the same task used to examine neuronal activity in the external and internal segments of globus pallidus (GPe and GPi) and ventral pallidum (VP). The presumed interstitial cells that are located within the laminae surrounding GPe and GPi and identified physiologically by their similarity with nbMc neurons, are referred to as border cells. A major finding of this study is that a large proportion of nbMc and border cells were active in relation to either the step-tracking movements or to load application. Moreover, a high proportion of the responses of border neurons were differential for opposite directions of load and movement. The percentages of directionally specific border and nbMc neurons were considerably less than for GP, with border neurons having more directionally specific responses than nbMc neurons. The similarity between border and GP neuronal properties in this task suggests that both may receive similar sensorimotor afferent input. In the compact portion of nbM, nonspecific neuronal responses following each behavioral event in the paradigm were common. These responses appeared to have been modified by and may have been contingent upon association with reinforcement.