title: Cortical visual evoked potentials recorded after optic tract near field stimulation during GPi-DBS in non-cooperative patients.
abstract: OBJECTIVE
  Neurophysiologic monitoring during deep brain stimulation (DBS) interventions in the globus pallidus internum (Gpi) for the treatment of Parkinson's disease or primary dystonia is generally based upon microelectrode recordings (MER); moreover, MER request sophisticated technology and high level trained personnel for a reliable monitoring. Recordings of cortical visual evoked potentials (CVEPs) obtained after stimulation of the optic tract may be a potential option to MER; since optic tract lies just beneath the best target for Gpi DBS, changes in CVEPs during intraoperative exploration may drive a correct electrode positioning.
  
  
  METHODS
  Cortical VEPs from optic tract stimulation (OT C-CEPs) have been recorded in seven patients during GPi-DBS for the treatment of Parkinson's disease and primary dystonia under general sedation. OT C-VEPs were obtained after near-field monopolar stimulation of the optic tract; recording electrodes were at the scalp. Cortical responses after optic tract versus standard visual stimulation were compared.
  
  
  RESULTS
  After intraoperative near-field OT stimulation a biphasic wave, named N40-P70, was detected in all cases. N40-P70 neither change in morphology nor in latency at different depths, but increased in amplitude approaching the optic tract. The electrode tip was positioned just 1mm above the point where OT-CVEPs showed the larger amplitude. No MERs were obtained in these patients; OT CVEPs were the only method to detect the Gpi before positioning the electrodes.
  
  
  CONCLUSIONS
  OT CVEPs seem to be as reliable as MER to detail the optimal target in Gpi surgery: in addition they are less expensive, faster to perform and easier to decode.
authors.affiliation: Department of Neurosurgery, University of Milano-Bicocca, San Gerardo Hospital, Monza, Italy. anland@libero.it
authors.forename: Andrea
authors.initials: A
authors.lastname: Landi
authors.forename: David
authors.initials: D
authors.lastname: Pirillo
authors.forename: Roberto
authors.initials: R
authors.lastname: Cilia
authors.forename: Angelo
authors.initials: A
authors.lastname: Antonini
authors.forename: Erik P
authors.initials: EP
authors.lastname: Sganzerla
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000768:Anesthesia, General; D046690:Deep Brain Stimulation; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D005917:Globus Pallidus / Q000502:physiology*; D006801:Humans; D008297:Male; D008839:Microelectrodes; D008875:Middle Aged; D010300:Parkinson Disease / Q000628:therapy; D010349:Patient Compliance; D010775:Photic Stimulation; D014795:Visual Pathways / Q000503:physiopathology*; D055815:Young Adult