Subthalamic nucleus deep brain stimulus evoked potentials: physiological and therapeutic implications.

The effect of subthalamic nucleus (STN) stimulation on cortical electroencephalographic activity was examined in 10 patients with Parkinson's disease and 4 patients with epilepsy. Evoked potentials were created by time-locking electroencephalography to the onset of electrical stimulation delivered through the lead implanted in the STN of patients who had previously undergone deep brain stimulation (DBS) surgery. The effect of different patterns of stimulation on the evoked response, including single- and paired-pulse as well as burst stimulation, was explored. Cortical evoked potentials to single pulses were observed with latencies as short as 1 to 2 msec after a single pulse of stimulation, with activity continuing, in some cases, for up to 400 msec. Paired-pulse experiments revealed refractory periods on the order of 0.5 msec, suggesting that stimulation of axons contributed to the generation of at least some portion of the evoked potential waveform. Evoked potentials were also present in response to 100-msec bursts of stimulation, with some evidence that the potential was initiated within the burst artifact. The potential implications of the types of responses observed as well as potential applications are discussed. Copyright 2002 Movement Disorder Society