title: Origin of far-field potentials in the ulnar compound muscle action potential.
abstract: BACKGROUND
  The compound muscle action potential (CMAP) following ulnar nerve stimulation receives a considerable contribution from far-field potentials (FFPs), although their origin is not entirely clear. We investigated this issue using voluntary contractions.
  
  
  METHODS
  In 7 control subjects, we placed multiple recording electrodes over the motor points of ulnar-innervated muscles. We asked the subjects to perform a weak movement corresponding to the action of each muscle, and identified the single motor unit potentials (MUPs) from that muscle. We summed the MUPs from each individual muscle and reconstructed the CMAPs.
  
  
  RESULTS
  The reconstructed CMAPs coincided well with the actual ones. The N1, P1, and early N2 components of the FFPs were generated primarily by palmar, but also by dorsal, interosseous muscles. The abductor digiti minimi muscle usually generated positive-negative biphasic FFPs, and the negative FFP generated the late N2 component.
  
  
  CONCLUSIONS
  These results should prompt a revision of the theory of FFP generation.
authors.affiliation: Department of Neurology, Teikyo University School of Medicine, Kaga 2-11-1, Itabashi-ku, Tokyo 1738605, Japan. sonoom@med.teikyo-u.ac.jp
authors.forename: Masahiro
authors.initials: M
authors.lastname: Sonoo
authors.forename: Katsumi
authors.initials: K
authors.lastname: Kurokawa
authors.forename: Mana
authors.initials: M
authors.lastname: Higashihara
authors.forename: Hiroko
authors.initials: H
authors.lastname: Kurono
authors.forename: Keiichi
authors.initials: K
authors.lastname: Hokkoku
authors.forename: Yuki
authors.initials: Y
authors.lastname: Hatanaka
authors.forename: Teruo
authors.initials: T
authors.lastname: Shimizu
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology*; D014459:Ulnar Nerve / Q000502:physiology*