The effect of electromagnetic stimulation of the posterior parietal cortex on eye movements

The posterior parietal cortex probably plays a central role in the sensorimotor transformations needed to make an accurate saccadic eye movement to a visual target. In an attempt to disrupt the normal programming of saccades, we magnetically stimulated the posterior parietal cortex in human volunteers, 80 ms after a small target moved 5 degrees horizontally from the centre of a VDU screen. Saccadic eye movements were recorded and experimental trials were compared with control, unstimulated trials. Magnetic stimulation was triggered in 70% of the trials selected randomly. The main effects of stimulation were: increased divergence of the eyes before each saccade, greater latency of saccade onset, and a tendency to undershoot the target. These results support the hypothesis that the posterior parietal cortex is involved in the programming of accurate saccades to visual targets.