Abstract
Objective: Associative motor cortical plasticity can be non-invasively induced by paired median nerve electric stimulation and transcranial magnetic stimulation (TMS) of the primary motor cortex (M1). This study investigates whether a simultaneous motor reaction of the other hand advances the associative plasticity in M1.Methods: Twenty-four right-handed subjects received conventional paired associative stimulation (PAS) and PAS with simultaneous motor reaction (PASmr) with at least a 1-week interval. The PASmr protocol additionally included left abductor pollicis brevis muscle movement responding to a digital sound. The motor reaction time was individually measured. The M1 excitability was examined by the motor evoked potential (MEP), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) before and after the PAS protocols.Results: The conventional PAS protocol significantly facilitated MEP and suppressed SICI. A negative correlation between the reaction time and the MEP change, and a positive correlation between the reaction time and the ICF change were found in the PASmr protocol. By subgrouping analysis, we further found significant facilitation of MEP and a reduction of ICF in the subjects with fast reaction times but not in those with slow reaction times.Conclusion: Synchronized motor reaction ipsilateral to the stimulated M1 induces associative M1 motor plasticity through the spike-timing dependent principle. MEP and ICF change could represent this kind of plasticity. The current findings provide a novel insight into designing rehabilitation programs concerning motor function.
Highlights
The motor cortical plasticity contributes to motor learning and appropriate movements (Sanes and Donoghue, 2000; McKay et al, 2002; Dayan and Cohen, 2011; Kida and Mitsushima, 2018; Kroneberg et al, 2018)
This study investigates whether intentional, active movements driven by the contralateral M1 influence the M1 plasticity induced by the conventional Paired associative stimulation (PAS) protocol
RmANOVA of the motor evoked potential (MEP) amplitude revealed a significant effect of time (F(1,23) = 6.21, P = 0.02; Table 2)
Summary
The motor cortical plasticity contributes to motor learning and appropriate movements (Sanes and Donoghue, 2000; McKay et al, 2002; Dayan and Cohen, 2011; Kida and Mitsushima, 2018; Kroneberg et al, 2018). A specific type of plasticity following Hebb’s theory, or known as the spiketiming dependent principle, has been found existing in the human motor cortex (M1) (Hebb, 1949; Müller-Dahlhaus et al, 2010). Has it been observed in the cell level, and in the systemic and behavioral level (Zhang et al, 1998; Stefan et al, 2000; Bi and Poo, 2001; Dan and Poo, 2004; Cooke and Bliss, 2006; Ziemann et al, 2008). The somatosensory inputs can be alternative from electric stimulation, passive movement to active movement once the spike-timing dependent principle is followed (Stefan et al, 2000; Thabit et al, 2010; Edwards et al, 2014)
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