Human pulvinar units, spontaneous activity and sensory-motor influences

Unit activity was recorded from the pulvinar nucleus (Pu) in human patients undergoing stereotaxic surgery. Thirty-six units (12 isolated and 12 pairs recorded with the same microelectrode) with a signal-to-noise ratio greater than 5, a stable amplitude, and a sustained discharge rate for more than 1 min, were selected for processing. The following functions were calculated with a digital computer to characterize discharge patterns: interval, autocorrelation and peristimulus time histograms for spikes, cross-correlation histograms between spikes of a pair, and autocorrelation functions and averages of the EEG. In spontaneous conditions, about half of the units fired in rhythmic bursts at the same or half the frequency of the Pu EEG. Most non-rhythmic units showed a "Poisson-like' interval histogram indicating a random firing pattern. Some non-rhythmic units revealed a periodic cross-correlation with the rhythmic Pu EEG, indicating that spikes tend to fire at a preferred phase of the rhythm. About half of the units showed phasic firing rate changes during voluntary movements. In most cells a discharge rate increase was observed. One unit also responded to passive movements of the fingers. Of the neurons tested, 2 out of 3 showed firing rate modulation during voluntary movements of the jaw as well as of the contralateral hand. The above units also increased the impulse rate after visual stimulation. Convergence of the effects of voluntary movements, and visual and auditory stimulation, was demonstrated in one unit. These results indicate the participation of the Pu in sensory-motor integrative functions.