Zhen Ni1, Robin F H Cash2, Carolyn Gunraj3, Eduard Bercovici3, Mark Hallett4, Robert Chen5. 1. Division of Neurology, Department of Medicine, University of Toronto and Krembil Research Institute, University Health Network, Toronto, Ontario, Canada; Human motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, USA. 2. Division of Neurology, Department of Medicine, University of Toronto and Krembil Research Institute, University Health Network, Toronto, Ontario, Canada; Monash Alfred Psychiatry Research Centre, Monash University Central Clinical School and The Alfred, Melbourne, VIC, Australia. 3. Division of Neurology, Department of Medicine, University of Toronto and Krembil Research Institute, University Health Network, Toronto, Ontario, Canada. 4. Human motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, USA. 5. Division of Neurology, Department of Medicine, University of Toronto and Krembil Research Institute, University Health Network, Toronto, Ontario, Canada. Electronic address: robert.chen@uhn.ca.
Abstract
BACKGROUND: Paired associative stimulation (PAS), with stimulus interval of 21.5 or 25 ms, using transcranial magnetic stimulation in the posterior-anterior (PA) current direction, produces a long-term-potentiation-like effect. Stimulation with PA directed current generates both early and late indirect (I)-waves while that in anterior-posterior (AP) current predominantly elicits late I-waves. Short interval intracortical inhibition (SICI) inhibits late I-waves but not early I-waves. OBJECTIVE: To investigate how cortical inhibition modulates the effects of PAS. METHODS: PAS at stimulus interval of 21.5 ms conditioned by SICI (SICI-PAS) was compared to PAS alone with both PA and AP directed currents. RESULTS: PAS with both current directions increased cortical excitability. SICI-PAS increased cortical excitability in the PA but not the AP current direction. CONCLUSIONS: Both early and late I-waves circuits can mediate cortical PAS plasticity under different conditions. Plasticity induction with the late but not the early I-wave circuits is blocked by SICI.
BACKGROUND:Paired associative stimulation (PAS), with stimulus interval of 21.5 or 25 ms, using transcranial magnetic stimulation in the posterior-anterior (PA) current direction, produces a long-term-potentiation-like effect. Stimulation with PA directed current generates both early and late indirect (I)-waves while that in anterior-posterior (AP) current predominantly elicits late I-waves. Short interval intracortical inhibition (SICI) inhibits late I-waves but not early I-waves. OBJECTIVE: To investigate how cortical inhibition modulates the effects of PAS. METHODS:PAS at stimulus interval of 21.5 ms conditioned by SICI (SICI-PAS) was compared to PAS alone with both PA and AP directed currents. RESULTS:PAS with both current directions increased cortical excitability. SICI-PAS increased cortical excitability in the PA but not the AP current direction. CONCLUSIONS: Both early and late I-waves circuits can mediate cortical PAS plasticity under different conditions. Plasticity induction with the late but not the early I-wave circuits is blocked by SICI.
Keywords:
Current direction; Intracortical circuit; Motor evoked potential; Paired associative stimulation; Primary motor cortex; Transcranial magnetic stimulation
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