Behavioural state affects saccadic eye movements evoked by microstimulation of striate cortex

We examine how behavioural conditions affect the manner in which electrical stimulation of striate cortex (V1) influences the generation of saccadic eye movements. Monkeys were trained (i) to acquire a fixation spot and remain fixated for juice reward and (ii) to acquire a fixation spot and generate a saccade to a visual target for reward. Electrical stimulation was delivered at various times during the execution of these tasks. For stimulation trials, pulses were delivered at 200 Hz using a 100- or 200-ms train duration. Currents as high as 1500 micro A were not sufficient to evoke saccades from V1 when monkeys were actively fixating a visual target, whereas current < 100 micro A was sufficient to evoke saccades when monkeys were not actively fixating. By interleaving trials in which a visual target was presented in the receptive field of stimulated neurons with nontarget stimulation trials, saccades could be evoked from V1 during the nontarget stimulation trials with currents as low as 2 micro A. The position of the visual target on the interleaved trials affected the probability of saccade evocation on the nontarget stimulation trials. Additional factors that affected the evoked saccades were time of reward delivery, ratio of stimulation to nonstimulation trials, and whether stimulation was delivered on the interleaved trials in which a target was positioned in the receptive field of the stimulated neurons. We argue that the behavioural state of an animal acts on the nigra-collicular pathway to lower the current threshold for the elicitation of saccades from V1.