Activity of forebrain neurons during alternating movements in cats

The firing pattern of single units in the precruciate cortex, globus pallidus, entopeduncular nucleus and ventral thalamus of cats was studied before alternating limb movements. Seventy-eight percent of the neurons in these regions of the brain changed their activity more than 500 msec before the movement. No consistent early EMG changes occurred in the proximal or axial muscles which would correlate with the early neuronal activity changes. The data suggest that the sequence of movements required for this alternation task appears to be 'set' well in advance of the activation of the muscles involved in the necessary postural adjustments or the response itself. In addition, the units which showed early activity changes may be involved in the mnemonic processing necessary to discriminate a situational context and make an appropriate response. Over 50% of the movement related units in the globus pallidus, entopeduncular nucleus and ventral thalamus were related to movement of both the contralateral and ipsilateral paws. By contrast, only 33% of cortical units showed this relationship to the movement. Therefore, this 'set' process may be a relatively non-lateralized process. The data support the concept that the basal ganglia are involved in the enabling and sequencing of movements rather than in directly causing them to occur.