Somatosensory evoked potential and clinical changes after electrode implant in basal ganglia of parkinsonian patients

Median nerve somatosensory evoked potentials (SEPs) were recorded in three parkinsonian patients who underwent electrode implant in the subthalamic nucleus and/or globus pallidus for chronic deep brain stimulation (DBS). SEPs were evoked before surgery, in a medication-free condition, and after the functional stereotactic procedure, before beginning DBS. In order to evaluate the timing of the SEP changes after the electrode implant, in three further patients SEPs were recorded within the operating theater, before and immediately after the implantation. Patients' symptoms improved immediately after the electrode implant, and both N20 and N30 amplitudes increased in the postsurgical SEP recording. The clinical and neurophysiological effects observed after surgery, before commencing DBS, can be explained by microdamage in the target nucleus following the electrode implant. They occurred also in the patients studied in the operating theater, thus suggesting that they occur immediately after the stereotactic procedure. Our results suggest that the circuitries between the basal ganglia and the primary sensorimotor cortex may be modified not only by DBS but also by microdamage due to surgery and that they exert an important influence on SEP amplitude.