The primate globus pallidus: neuronal activity related to direction of movement

Neurons in the arm areas of the external and internal segments of the globus pallidus (GPe and GPi) and the ventral pallidum (VP) have been examined in a visuomotor step-tracking task. This task, which was similar to that used previously to examine neurons in the arm area of the putamen, dissociated the direction of movement from the pattern of muscle activity associated with the movement. The major finding of the present study is that, as in the putamen, the activity of almost half of the neurons in GPe and GPi was related to the direction of movement. Cells with overall patterns of activity similar to muscle were rare, although many neurons had static and/or dynamic load effects which resembled those seen in muscle. Responses of neurons to load application have also been examined in this paradigm in order to determine the nature of possible somatosensory input. Short-latency "sensory" responses to load application were found in pallidum as previously in putamen, but, by contrast, they occurred somewhat later and included bidirectional responses. Similar proportions of cells in GP and putamen were related to static loads. Some VP neurons appeared to encode information about specific features of the trials, but the majority of responses were nonspecific suggesting relations to more general features of the task.