title: Neurophysiological mechanism of possibly confounding peripheral activation of the facial nerve during corticobulbar tract monitoring.
abstract: OBJECTIVE
  To improve the recognition and possibly prevent confounding peripheral activation of the facial nerve caused by leaking transcranial electrical stimulation (TES) current during corticobulbar tract monitoring.
  
  
  METHODS
  We applied a single stimulus and a short train of electrical stimuli directly to the extracranial portion of the facial nerve. We compared the peripherally elicited compound muscle action potential (CMAP) of the facial nerve with the responses elicited by TES during intraoperative monitoring of the corticobulbar tract.
  
  
  RESULTS
  A single stimulus applied directly to the facial nerve at subthreshold intensities did not evoke a CMAP, whereas short trains of subthreshold stimuli repeatedly evoked CMAPs. This is due to the phenomenon of sub- or near-threshold super excitability of the cranial nerve. Therefore, the facial responses evoked by short trains TES, when the leaked current reaches the facial nerve at sub- or near-threshold intensity, could lead to false interpretation.
  
  
  CONCLUSIONS
  Our results revealed a potential pitfall in the current methodology for facial corticobulbar tract monitoring that is due to the activation of the facial nerve by subthreshold trains of stimuli. This study proposes a new criterion to exclude peripheral activation during corticobulbar tract monitoring.
  
  
  CONCLUSIONS
  The failure to recognize and avoid facial nerve activation due to leaking current in the peripheral portion of the facial nerve during TES decreases the reliability of corticobulbar tract monitoring by increasing the possibility of false interpretation.
authors.affiliation: Department of Intraoperative Neurophysiology, Mount Sinai Health System, Roosevelt Hospital, New York, NY, USA.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Téllez
authors.affiliation: Department of Intraoperative Neurophysiology, Mount Sinai Health System, Roosevelt Hospital, New York, NY, USA. Electronic address: su1969july@outlook.com.
authors.forename: Sedat
authors.initials: S
authors.lastname: Ulkatan
authors.affiliation: Department of Clinical Neurophysiology, Complejo Hospitalario de Navarra, Pamplona, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Urriza
authors.affiliation: Department of Clinical Neurophysiology, Gregorio Marañón University Hospital, Madrid, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Arranz-Arranz
authors.affiliation: Department of Intraoperative Neurophysiology, Mount Sinai Health System, Roosevelt Hospital, New York, NY, USA.
authors.forename: Vedran
authors.initials: V
authors.lastname: Deletis
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D005154:Facial Nerve / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010525:Peripheral Nerves / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Corticobulbar tract; Cranial nerve; Hyperexcitability; Intraoperative monitoring; Motor-evoked potential; Near-threshold