Delaying forelimb responses by microstimulation of macaque V1.

Electrical microstimulation of macaque V1 has previously been shown to delay saccadic eye movements made to a punctate visual target placed in the receptive field of the stimulated neurons. It remains unclear whether this delay effect is specific to the oculomotor system or whether the effect can be demonstrated in the skeletomotor system as well. To address this question, a rhesus monkey was trained to depress a left or right lever with its respective hand in response to a visual target presented in the left or right hemifield. On 50% of trials, a 100 ms train of stimulation consisting of 100 microA, 0.2-ms anode-first pulses was delivered to the neurons before the onset of the visual target. Stimulation of V1 delayed the execution of the lever response when the visual target was positioned within the receptive field of the stimulated neurons. We suggest that the delay effect induced by microstimulation of V1 is largely due to a disruption of the visual signal as it is transmitted along the geniculostriate pathway.