title: Excitability of the primary motor cortex increases more strongly with slow- than with normal-speed presentation of actions.
abstract: BACKGROUND
  The aim of the present study was to investigate how the speed of observed action affects the excitability of the primary motor cortex (M1), as assessed by the size of motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS).
  
  
  METHODS
  Eighteen healthy subjects watched a video clip of a person catching a ball, played at three different speeds (normal-, half-, and quarter-speed). MEPs were induced by TMS when the model's hand had opened to the widest extent just before catching the ball ("open") and when the model had just caught the ball ("catch"). These two events were locked to specific frames of the video clip ("phases"), rather than occurring at specific absolute times, so that they could easily be compared across different speeds. MEPs were recorded from the thenar (TH) and abductor digiti minimi (ADM) muscles of the right hand.
  
  
  RESULTS
  The MEP amplitudes were higher when the subjects watched the video clip at low speed than when they watched the clip at normal speed. A repeated-measures ANOVA, with the factor VIDEO-SPEED, showed significant main effects. Bonferroni's post hoc test showed that the following MEP amplitude differences were significant: TH, normal vs. quarter; ADM, normal vs. half; and ADM, normal vs. quarter. Paired t-tests showed that the significant MEP amplitude differences between TMS phases under each speed condition were TH, "catch" higher than "open" at quarter speed; ADM, "catch" higher than "open" at half speed.
  
  
  CONCLUSIONS
  These results indicate that the excitability of M1 was higher when the observed action was played at low speed. Our findings suggest that the action observation system became more active when the subjects observed the video clip at low speed, because the subjects could then recognize the elements of action and intention in others.
authors.affiliation: Unit of Rehabilitation Sciences, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan; Medical Corporation Tojinkai Miharadai Hospital, Nagasaki, Japan.
authors.forename: Takefumi
authors.initials: T
authors.lastname: Moriuchi
authors.affiliation: Unit of Rehabilitation Sciences, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan; Medical Corporation Tojinkai Miharadai Hospital, Nagasaki, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Iso
authors.affiliation: Unit of Rehabilitation Sciences, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan; Japanese Red Cross Society Nagasaki Genbaku Hospital, Nagasaki, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Sagari
authors.affiliation: Faculty of Health and Social Work, School of Rehabilitation, Kanagawa University of Human Services, Kanagawa, Japan.
authors.forename: Kakuya
authors.initials: K
authors.lastname: Ogahara
authors.affiliation: Center for Industry, University and Government Cooperation, Nagasaki University, Nagasaki, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Kitajima
authors.affiliation: Unit of Physical and Occupational Therapy, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Tanaka
authors.affiliation: Faculty of Rehabilitation Sciences, Nishikyushu University, Saga, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Tabira
authors.affiliation: Unit of Rehabilitation Sciences, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Higashi
mesh_terms: D000328:Adult; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D014796:Visual Perception / Q000502:physiology*