Deep brain stimulation of the subthalamic nucleus in Parkinson's disease: similar improvements in saccadic and manual responses.

The purpose of this study was to determine whether the very large effects of saccadic latency distribution, generated by deep brain stimulation of the subthalamic nuclei are reflected in quantitatively corresponding changes for manual responses, rather than representing a reflection of the specific role of the subthalamus in controlling saccades. Saccadic and manual reaction times were measured under as nearly identical conditions as possible in six patients with implanted subthalamic electrodes and in six age-matched controls with the stimulation either on or off. Median latency was found to be reduced by stimulation in a similar way to saccadic latency; in neither case was there a significant change in the Linear Approach to Threshold with Ergotic Rate parameter σ. For both types of response, the effect is to move the responses proportionately in the direction of average of responses in the control group. We therefore conclude that the previously described effects of stimulation on latency are not a phenomenon peculiar to saccades, increasing confidence in using saccadic latency measurements as a surrogate for more general responses when determining the efficacy of deep brain stimulation.