title: Characteristics and distribution of somatosensory evoked potentials in the subthalamic region.
abstract: OBJECTIVE
  The aim of the present study is to evaluate the topographical distribution of somatosensory evoked potentials (SSEPs) in the subthalamic area, including the zona incerta (ZI). Determination of this distribution may help in the correct placement of deep brain stimulation (DBS) leads.
  
  
  METHODS
  Intraoperative SSEPs were recorded from contacts of DBS electrodes at 221 sites in 41 patients: three patients with essential tremor and 38 with Parkinson disease who underwent implantation of DBS electrodes for the relief of severe tremor or parkinsonism.
  
  
  RESULTS
  Two distinct SSEPs were recorded in the subthalamic area. One was a monophasic positive wave with a mean latency of 15.8 +/- 0.9 msec, which the authors designated subthalamic P16. Using both cephalic and noncephalic references, subthalamic P16 was only recorded in the ventral part of the ZI (mean 6.6 +/- 1.3 mm posterior to the midcommissure point, 4.8 +/- 1.2 mm inferior to the anterior commissure-posterior commissure line, and 9.7 +/- 0.6 mm lateral to the midline). When bipolar recordings were made, the traces showed a phase reversal at the caudal part of the ZI. The second potential is a positive-negative SSEP recorded throughout the entire subthalamic area. The mean latencies of the initial positive peak and the major negative peak were 13.6 +/- 1.1 msec and 16.4 +/- 1.1 msec, respectively. Several small notches were superimposed on the peaks, and their amplitudes were largest at the contact close to the medial lemniscus.
  
  
  CONCLUSIONS
  The results indicate that intraoperative SSEPs from DBS electrodes are helpful in refining stereotactic targets in the thalamus and subthalamic areas.
authors: Department of Neurology, Sapporo Azabu Neurosurgical Hospital, Sapporo, Japan. kitagawa-jscn@umin.ac.jp
authors: Mayumi
authors: M
authors: Kitagawa
authors: Jun-ichi
authors: J
authors: Murata
authors: Haruo
authors: H
authors: Uesugi
authors: Ritsuko
authors: R
authors: Hanajima
authors: Yoshikazu
authors: Y
authors: Ugawa
authors: Hisatoshi
authors: H
authors: Saito
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D046690:Deep Brain Stimulation; D004567:Electrodes, Implanted; D020329:Essential Tremor / Q000503:physiopathology* / Q000628:therapy; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve; D008875:Middle Aged; D010300:Parkinson Disease / Q000503:physiopathology* / Q000628:therapy; D011930:Reaction Time / Q000502:physiology; D020530:Subthalamus / Q000503:physiopathology*