title: P9 in median nerve SEPs is a junctional potential generated by the change of the volume conductor size between trunk and neck.
abstract: OBJECTIVE
  We aimed to investigate the origin of P9 in median SEPs by applying the junctional potential theory.
  
  
  METHODS
  We studied the distribution over the body surface with contralateral shoulder reference in 4 normal subjects.
  
  
  RESULTS
  A stationary potential field P9/tN9 (=truncal N9) was recorded: P9 over head and neck (the smaller part), tN9 over trunk (the larger part), the boundary being located between trunk and neck. This polarity agreed with that expected from simulation studies.
  
  
  CONCLUSIONS
  P9 is a junctional potential generated by the change of the volume conductor size between trunk and neck.
authors.affiliation: Department of Neurology, Teikyo University School of Medicine, Tokyo, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Mochizuki
authors.forename: M
authors.initials: M
authors.lastname: Sonoo
authors.forename: T
authors.initials: T
authors.lastname: Shimizu
authors.forename: M
authors.initials: M
authors.lastname: Iwata
mesh_terms: D018780:Body Surface Potential Mapping; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D006801:Humans; D008475:Median Nerve / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology*