Microstimulation of V1 delays the execution of visually guided saccades

Electrical stimulation delivered to V1 concurrently with the presentation of a visual target interferes with both the selection and the detection of targets positioned in the receptive field of the stimulated neurons. In the present study, we examined the temporal course of this effect by delivering electrical stimulation to V1 of rhesus monkeys at various times before the appearance of a visual target. Each trial was initiated by the appearance of a fixation spot that, once acquired, was followed by the presentation of a visual target in the receptive field of the stimulated neurons. A monkey was reward after making a saccadic eye movement to the target. A delay in saccade generation was obtained when stimulation was delivered while an animal maintained fixation on the fixation spot. No delay occurred when the visual target was placed outside the receptive field of the stimulated neurons. The best parameters for inducing the saccadic delay were: (i) anode-first pulses (as opposed to cathode-first pulses) and (ii) train durations greater than 40 ms and frequencies greater than 100 Hz. The lowest current threshold for producing a saccadic delay occurred at 1.5 mm below the top of superficial V1. The chronaxies of the directly stimulated elements mediating the delay ranged from 0.13 to 0.24 ms. These values overlap with those that have been described for phosphene induction in human V1. We discuss how the elements mediating the saccadic delay might interrupt a visual signal as it passes along the geniculostriate pathway.