Pallidal Activity Related to Posture and Movement during Reaching in the Cat

We tested the hypothesis that the pallidum contributes to the control of both posture and movement. We recorded neuronal activity from the pallidum in a task in which male cats reached forward from a standing posture to depress a lever. In agreement with previous studies, we found that a majority of pallidal cells (91/116, 78%), including neurons in both the entopeduncular nucleus and the globus pallidus, showed significant modulation of their activity during reaching with the contralateral limb. Mostly different populations of cells were active during the transport (flexion) and lever press (extension) phase of the task. Most cells showed dynamic patterns of activity related to the movement. However, a modest proportion of modulated cells (18/91, 20%) showed properties consistent with a contribution to the control of anticipatory postural responses, whereas a further 10% showed activity consistent with a contribution to postural support during the movement. Although some cells that showed modified activity only during reaches with the contralateral forelimb, many cells (65/91, 71%) were also activated during reaches with the ipsilateral forelimb. This was particularly true for cells related to the lever press, many of which discharged similarly during reaches of either limb. This suggests a context-dependent control of movement and posture in which the same muscles are used for different functions during contralateral and ipsilateral reach. Comparison with the results from recordings made previously from the motor cortex and the pontomedullary reticular formation in the same task show more similarities with the former than the latter.SIGNIFICANCE STATEMENT Pathologic changes in basal ganglia function frequently lead to problems with postural stability and gait initiation. Here, we show that some neurons in one of the output regions of the basal ganglia, the pallidum, show discharge activity compatible with a contribution to postural control. At the same time, we note that such cells are a minority in this region with most cells being related to movement rather than posture. We also show that many neurons are active during movements of both the contralateral and ipsilateral limbs, sometimes with identical discharge patterns. We suggest that this indicates a context-dependent regulation of movement and posture in the pallidum.