title: Effect of the inhibitory phenomenon following magnetic stimulation of cortex on brainstem motor neuron excitability and on the cortical control of brainstem reflexes.
abstract: We studied the effect of the inhibitory phenomenon following transcranial magnetic stimulation (TMS) on brainstem motor neuron excitability and on the cortical control of brainstem reflexes in 5 normal subjects. The R1 component of the blink reflex assessed excitability of the facial nucleus during the period of post-TMS inhibition (experiment 1). TMS effect on the cortical control of brainstem reflexes was assessed by delivery of a stimulus that was less than or equal to the threshold for the R1 with the subject relaxed, yet elicited a potentiated reflex during maneuvers requiring cortical input (i.e., voluntary eye-closure and anticipation, experiment 2). In experiment 1, a suprathreshold electric stimulus applied during post-TMS inhibition elicited an R1 response that was preserved in amplitude (mean 476 +/- 44 microV; 123%) compared to control responses not preceded by TMS (mean 386 +/- 31 microV). Conversely, in experiment 2, when the R1 was dependent on cortical drive, the mean R1 amplitude during post-TMS inhibition was only 15% (P < 0.01) and 8% (P < 0.01) of control values obtained during eye-closure and anticipation, respectively. These findings imply that the inhibition following TMS originates rostral to the facial nucleus, at a cortical level.
authors.affiliation: Department of Neurology, University of Mississippi Medical Center, Jackson 39216-4505.
authors.forename: A A
authors.initials: AA
authors.lastname: Leis
authors.forename: M
authors.initials: M
authors.lastname: Kofler
authors.forename: D S
authors.initials: DS
authors.lastname: Stokic
authors.forename: G J
authors.initials: GJ
authors.lastname: Grubwieser
authors.forename: J S
authors.initials: JS
authors.lastname: Delapasse
mesh_terms: D000328:Adult; D001767:Blinking / Q000502:physiology*; D001933:Brain Stem / Q000502:physiology*; D002540:Cerebral Cortex / Q000502:physiology*; D004558:Electric Stimulation; D006801:Humans; D008280:Magnetics; D009046:Motor Neurons / Q000502:physiology*; D009801:Oculomotor Muscles / Q000294:innervation / Q000502:physiology; D009882:Ophthalmic Nerve / Q000502:physiology; D012016:Reference Values