title: The human hand motor area is transiently suppressed by an unexpected auditory stimulus.
abstract: OBJECTIVE
  To study the effect of a loud auditory stimulus on the excitability of the human motor cortex.
  
  
  METHODS
  Ten normal volunteers participated in this study. The size of responses to transcranial magnetic or electrical cortical stimulation (TMS or TES) given at different times (ISIs) after a loud sound were compared with those to TMS or TES alone (control response). Different intensities and durations of sound were used at several intertrial intervals (ITIs). In addition, we examined how the presence of a preceding click modulated the effect of a loud sound (prepulse inhibition). The incidence of startle response evoked by various stimuli was also studied.
  
  
  RESULTS
  A loud auditory stimulus suppressed EMG responses to TMS when it preceded the magnetic stimulus by 30-60 ms, whereas it did not affect responses to TES. This suggests that the suppression occurred at a cortical level. Significant suppression was evoked only when the sound was louder than 80 dB and longer than 50 ms in duration. Such stimuli frequently elicited a startle response when given alone. The effect was not evoked if the ITI was 5 s, but was evoked when it was longer than 20 s. A preceding click reduced the suppression elicited by loud sounds.
  
  
  CONCLUSIONS
  Auditory stimuli that produced the greatest effect on responses to TMS had the same characteristics as those which yielded the most consistent auditory startle. We suggest that modulation of cortical excitability occurs in parallel with the auditory startle and both may arise from the same region of the brain-stem.
authors.affiliation: Department of Neurology, Graduate School of Medicine, University of Tokyo, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Furubayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Ugawa
authors.forename: Y
authors.initials: Y
authors.lastname: Terao
authors.forename: R
authors.initials: R
authors.lastname: Hanajima
authors.forename: K
authors.initials: K
authors.lastname: Sakai
authors.forename: K
authors.initials: K
authors.lastname: Machii
authors.forename: H
authors.initials: H
authors.lastname: Mochizuki
authors.forename: Y
authors.initials: Y
authors.lastname: Shiio
authors.forename: H
authors.initials: H
authors.lastname: Uesugi
authors.forename: H
authors.initials: H
authors.lastname: Enomoto
authors.forename: I
authors.initials: I
authors.lastname: Kanazawa
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D004569:Electroencephalography / Q000379:methods*; D004576:Electromyography; D006185:Habituation, Psychophysiologic; D006225:Hand / Q000294:innervation*; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation*; D012016:Reference Values; D013216:Reflex, Startle / Q000502:physiology*; D013997:Time Factors