Saccade and blinking evoked by microstimulation of the posterior parietal association cortex of the monkey

Summary

Electrical stimulation with microelectrodes of the posterior parietal association cortex in alert behaving monkeys elicited saccadic eye movements and blinking. The sites in which saccades were elicited by electrical stimulation were concentrated in the anteromedial part of area 7a, especially in the posterior bank of the intraparietal sulcus, in a region which sends efferent projections to the frontal eye field and the superior colliculus, but they were also found in the posterolateral part of area 7a. Compared with the frontal eye fields and the superior colliculus, the threshold current for eliciting saccades was relatively high, on the average 86 μA. Moreover, the elicitation of saccade was inconsistent even with suprathreshold stimulation and suppressed during visual fixation. Latencies of the saccades were relatively long, on the average 50 ms; they were longer in the posterolateral part than in the anteromedial part. Direction and amplitude of evoked saccades depended on the site of stimulation, but was independent of eye position in most cases. However, “goal-directed” saccades which depended on initial eye position were elicited in three penetrations in the posterolateral part of area 7a. Blinking was elicited mainly in the lateral part of area 7a. The threshold of blinking was 70 μA and the latency was 50 ms on the average. In contrast to saccades, blinking was elicited constantly with each stimulus even during attentive fixation. We occasionally recorded single unit activity at the site of stimulation with the same electrodes. More than half of the units recorded at the site of blinking responded to approaching visual stimulus. These results suggest that area 7a participates indirectly in the control of saccades by way of its connection to the frontal eye fields or the superior colliculus, and it may also play an important role in blinking in response to a visual threat.