title: Effects of motor cortical stimulation on the excitability of contralateral motor and sensory cortices.
abstract: Single pulses of transcranial magnetic stimulation (TMS) were applied to the right hemisphere over either the hand sensory area, the hand motor area (M1), ventral premotor area (vPM), dorsolateral prefrontal cortex, or 10 cm away from head (sham stimulation) in order to test the effect on motor evoked potentials (MEPs) elicited by single pulse TMS or transcranial electrical stimulus (TES) over the left M1 or the somatosensory evoked potential (SEP) elicited by an electrical stimulus to the right median nerve. The interstimulus intervals (ISIs) for MEP experiments were 50, 100, 150, 200, 300 and 400 ms, with those for SEP experiments being adjusted for the impulse conduction time from the wrist to the cortex. TMS over the right M1 reduced MEPs elicited by TMS of the left motor cortex at ISIs of 50-150 ms, whereas MEPs produced by TES were unaffected. TMS over M1 and vPM facilitated the contralateral cortical median nerve SEPs at an ISI of 100-200 ms, whereas it had no effect on tibial nerve SEPs or paired median nerve stimulation SEP. Based on these results, we conclude that at around 150-ms intervals, TMS over the motor areas (M1 and vPM) reduces the excitability of the contralateral motor area. This has a secondary effect of enhancing the responsiveness of the sensory cortex through cortico-cortical connections.
authors.affiliation: Department of Neurology, Division of Neuroscience, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo Bunkyo-ku, 113-8655 Tokyo, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Mochizuki
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Terao
authors.forename: Shingo
authors.initials: S
authors.lastname: Okabe
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Furubayashi
authors.forename: Noritoshi
authors.initials: N
authors.lastname: Arai
authors.forename: Nobue K
authors.initials: NK
authors.lastname: Iwata
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Hanajima
authors.forename: Keiko
authors.initials: K
authors.lastname: Kamakura
authors.forename: Kazuo
authors.initials: K
authors.lastname: Motoyoshi
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ugawa
mesh_terms: D000328:Adult; D000704:Analysis of Variance; 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*; D013003:Somatosensory Cortex / Q000502:physiology*