Early visuomotor integration processes induce LTP/LTD-like plasticity in the human motor cortex.
To investigate whether visuomotor integration processes induce long-term potentiation (LTP) and depression (LTD)-like plasticity in the primary motor cortex (M1), we designed a new paired associative stimulation (PAS) protocol coupling left primary visual area (V1) activation achieved by hemifield visual evoked potentials (VEPs) and transcranial magnetic stimulation (TMS) over the left M1, at specific interstimulus intervals (ISIs), delivered at 1 Hz (V-PAS). Before and after V-PAS, we measured motor evoked potentials (MEPs). To clarify the mechanisms underlying V-PAS, we tested the effect of 1-Hz repetitive TMS (rTMS), 0.25-Hz V-PAS and rTMS, and a shorter 0.25-Hz V-PAS protocol. To examine V-PAS with contralateral V1 activation, we delivered V-PAS activating the right V1. To clarify whether V-PAS increases V1 activity or parieto- and premotor-to-M1 connectivity, before and after V-PAS, we examined VEPs and MEPs evoked by paired-pulse techniques. V-PAS increased, decreased, or left MEPs unchanged according to the ISI used. After 1-Hz rTMS MEPs decreased. Although 0.25-Hz rTMS elicited no aftereffect, 0.25-Hz V-PAS modulated MEPs according to the ISI used. The short 0.25-Hz V-PAS protocol left MEPs unchanged. Contralateral V-PAS inhibited MEPs. After V-PAS, VEPs remained unchanged and the premotor-to-M1 inhibitory connections decreased. V-PAS induces M1 LTP/LTD-like plasticity by activating premotor-to-motor connections.
IRCCS Neuromed Institute, Pozzilli (IS), Italy.
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Suppa
IRCCS Neuromed Institute, Pozzilli (IS), Italy.
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Li Voti
Department of Neurology and Psychiatry.
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Rocchi
Department of Physiology and Pharmacology, "Sapienza" University of Rome, 00185 Rome, Italy.
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Papazachariadis
IRCCS Neuromed Institute, Pozzilli (IS), Italy Department of Neurology and Psychiatry.
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Berardelli
D000328:Adult; D019054:Evoked Potentials, Motor; D005074:Evoked Potentials, Visual; D005260:Female; D006801:Humans; D017774:Long-Term Potentiation; D036881:Long-Term Synaptic Depression; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D014793:Visual Cortex / Q000502:physiology*; D055815:Young Adult
paired associative stimulation; primary motor cortex; rTMS; visual evoked potentials; visuomotor integration