Cortical mechanisms mediating the inhibitory period after magnetic stimulation of the facial motor area

G. Cruccu, M. Inghilleri, A. Berardelli, A. Romaniello, M. Manfredi

Research output: Contribution to journalArticlepeer-review

Abstract

We studied the silent period (SP) that interrupts voluntary electromyographic activity (EMG) in facial muscles, after transcranial magnetic stimulation (TMS), in normal subjects. High-intensity magnetic stimulation with a 12-cm round coil centered at the vertex induced a long- lasting SP (215 ms), whereas supramaximal stimulation of the facial nerve only induced a short (<20 ms) and incomplete EMG suppression, and cutaneous stimuli had no inhibitory effect at all. Cutaneous trigeminal stimulation delivered after TMS evoked blink-like reflexes, showing that facial motoneurons were not inhibited during the SP. Simultaneous recordings from perioral muscles (large cortical representation) and from orbicularis oculi and masseter muscles (small cortical representation) showed SPs of identical duration. Focal stimuli with a figure-of-eight coil showed that positioning of the coil was critical and that the optimal scalp sites for evoking the largest motor potentials and longest SPs coincided. Low-intensity stimulation occasionally elicited short SPs without a preceding motor potential. We conclude that the SP induced in facial muscles by TMS results from the excitation of cortical inhibitory interneurons surrounding the upper motoneurons.

Original languageEnglish
Pages (from-to)418-424
Number of pages7
JournalMuscle and Nerve
Volume20
Issue number4
DOIs
Publication statusPublished - 1997

Keywords

  • facial muscle
  • human
  • motor cortex
  • silent period
  • transcranial magnetic stimulation

ASJC Scopus subject areas

  • Clinical Neurology
  • Neuroscience(all)

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