Enhancement of visual responses of area 7 neurons by electrical pre-conditioning stimulation of LP-pulvinar nuclei of the monkey.

The characteristics of visually evoked unit responses in area PG of the infraparietal lobule were studied in the awake trained Rhesus monkey. These responses are shown to be significantly modified by pairing the visual stimulus with pre-conditioning stimulation of targets in the LP Pulvinar complex. Pre-conditioning stimuli were either single pulses, or a 50 ms train of pulses at 100 Hz delivered through bipolar electrodes 20 ms prior to, simultaneously with, or 50 ms following the visual stimulus. In some cases, modifications of the visual responses appeared as more massive discharges; in others they became bursts of constant latencies, pattern and duration, that contained high frequency discharges. A pre-conditioning single stimulus delivered simultaneously to a few sites in the LP, medial and lateral pulvinar was more effective than stimulation at a single electrode site, and produced an enhancement that appeared like an additive effect of several inputs. In the enhanced condition, repetition of single pulse preconditioning stimulation resulted in a considerable build-up of the enhancement. A pre-conditioning train of stimuli delivered during enhancement resulted in a further increase in the constancy of response durations and patterns. These changes, lasting as long as five minutes, manifested hysteresis: when recovery was allowed without any pre-conditioning stimulation, the various response patterns appeared in a reverse order. It is proposed that this dependence of the responses on the neural state is based on a complex network of inputs to cells of area 7.