title: Asymmetric bilateral effect of the supplementary motor area proper in the human motor system.
abstract: OBJECTIVE
  This study aimed to clarify the function of human supplementary motor area proper (SMA) by the single-pulse electric stimulation method and its clinical usefulness for SMA mapping.
  
  
  METHODS
  We studied five patients with epilepsy or brain tumour who underwent invasive functional mapping with subdural electrodes. Single-pulse electric stimulation of primary motor area (MI) and SMA was carried out through pairs of subdural electrodes, and motor-evoked potentials (MEPs) were recorded from surface electromyogram on both sides and also cortico-cortical-evoked potentials (CCEPs) from electrocorticogram.
  
  
  RESULTS
  SMA stimulation elicited: (1) MEPs and following silent periods (SPs) in the contralateral upper and lower extremities, (2) SPs with or without minimal MEPs in the ipsilateral upper extremity and (3) CCEPs in the somatotopically corresponding region of the ipsilateral MI. Compared with MI stimulation, SMA stimulation required higher stimulus intensities (mean 14.2 mA (SMA) vs. 8.5 mA (MI)) to elicit MEPs and showed significantly longer onset latencies in upper extremity (range: 4-10 ms).
  
  
  CONCLUSIONS
  The results demonstrated an asymmetric bilateral effect of human SMA upon the corticospinal pathway.
  
  
  CONCLUSIONS
  Single-pulse electric cortical stimulation would be clinically useful for distinguishing SMA from MI. The asymmetric bilateral effect of SMA might be conveyed through the direct descending pathway.
authors.affiliation: Department of Neurosurgery, Kyoto University Graduate School of Medicine, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 6068507, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kikuchi
authors.forename: Riki
authors.initials: R
authors.lastname: Matsumoto
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Mikuni
authors.forename: Yohei
authors.initials: Y
authors.lastname: Yokoyama
authors.forename: Atsuhito
authors.initials: A
authors.lastname: Matsumoto
authors.forename: Akio
authors.initials: A
authors.lastname: Ikeda
authors.forename: Hidenao
authors.initials: H
authors.lastname: Fukuyama
authors.forename: Susumu
authors.initials: S
authors.lastname: Miyamoto
authors.forename: Nobuo
authors.initials: N
authors.lastname: Hashimoto
mesh_terms: D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology