• Ritsuko Hanajima, Jonathan O Dostrovsky, Andres M Lozano, William D Hutchison, Karen D Davis, Robert Chen, and Peter Ashby.
• Toronto Western Research Institute, Toronto Western Hospital, 399 Bathurst St., Toronto, ON M5T 2S8, Canada. hanajima_tky@umin.ac.jp
• Clin Neurophysiol. 2004 Feb 1; 115 (2): 424-34.

ObjectiveTo examine the location of deep brain stimulation (DBS) electrode somatosensory evoked potentials (SEPs) and determine the generators of the median nerve SEPs recorded in thalamus and subthalamic nucleus (STN).MethodsSEPs were recorded from contacts of DBS electrodes and microelectrodes in thalamus and STN to establish the latencies of N13, N18 and N20 in 24 patients (8 tremor, 4 chronic pain, 12 Parkinson disease) undergoing chronic DBS.ResultsA large SEP with a mean latency of 17.9+/-1.7 ms was recorded from thalamic contacts. Phase reversal occurred at the horizontal level of the anterior commissure-posterior commissure line. Smaller potentials with similar latency but no reversal could be recorded from STN electrodes.ConclusionsWe propose that the thalamic SEP is generated by excitatory post-synaptic potentials in sensory relay neurons in nucleus ventrocaudalis. A small potential in STN at a similar latency, may be due to volume conduction from thalamus. Intraoperative and postoperative SEP recordings from DBS electrodes could be used to determine the optimal position of the contacts relative to the sensory pathways and the choice of contacts for chronic stimulation.

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