Discharge patterns of basal ganglia neurons during active maintenance of postural stability and adjustment to chair tilt.

Neurons in the putamen and globus pallidus were studied in awake monkeys making active postural adjustments during static and dynamic chair tilt. When the chair was held horizontal and the monkey actively maintained a restricted head position, neurons had tonic firing rats similar to those described previously, with low frequency patterns in the putamen and low frequency-burst or intermediate (IFD) to high frequency (HFD) tonic patterns in neurons in the pallidal segments. Over half of the neurons with IFD or HFD discharge rates and a smaller proportion of those with slow discharge rates showed changes in firing that were temporally correlated with chair tilt. Phase shifts of firing frequency relative to sinusoidally vaired chair position varied in units with different tonic discharge frequencies. Maximum and minimum discharge rates in IFD neurons occurred near maximum chair velocities, whereas the phase shift decreased in HFD neurons, which had higher discharge rates during the horizontal chair position. Neurons with changes in discharge during chair tilt were found in all portions of the putamen and globus pallidus studied.