Mechanism of the silent period following transcranial magnetic stimulationEvidence from epidural recordings |
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| Authors: | R. Chen Andres M. Lozano Peter Ashby |
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| Affiliation: | (1) Division of Neurology and Playfair Neuroscience Unit, Toronto Western Hospital, University Health Network, University of Toronto, EC8–025, 399 Bathurst Street, Toronto, Ontario, Canada M5T 2S8, e-mail: t49mdns@torhosp.toronto.on.ca, Tel: +1-416-603-5927, Fax: +1-416-603-5768, CA;(2) Division of Neurosurgery and Playfair Neuroscience Unit, Toronto Western Hospital, University Health Network, University of Toronto, XX |
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| Abstract: | We investigated the nature of the silent period (SP) following transcranial magnetic stimulation by recording corticospinal volleys in a patient with implanted cervical epidural electrodes. Single suprathreshold test stimuli and paired stimuli at interstimulus intervals (ISIs) of 50–200 ms were delivered while the subject maintained a constant background contraction. The silent period duration from a single test stimulus was 357±62 ms. The test motor-evoked potentials were markedly reduced at all the ISIs tested. The I (indirect) waves induced by the test stimulus were largely unchanged at an ISI of 50 ms, suggesting that there was little change in motor cortex excitability. However, the corticospinal volleys, especially the late I waves, were substantially reduced at ISIs of 100 ms, 150 ms, and 200 ms. Our findings suggest that the early part of the SP is mainly due to spinal mechanisms, while the late part of the SP is related to reduced motor cortex excitability. Received: 21 January 1999 / Accepted: 14 April 1999 |
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| Keywords: | Silent period Transcranial magnetic stimulation Motor cortex Epidural recordings Human |
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