Abstract
BackgroundSkill learning engages offline activity in the primary motor cortex (M1). Sensorimotor cortical activity oscillates between excitatory trough and inhibitory peak phases of the mu (8–12 Hz) rhythm. We recently showed that these mu phases influence the magnitude and direction of neuroplasticity induction within M1. However, the contribution of M1 activity during mu peak and trough phases to human skill learning has not been investigated. ObjectiveTo evaluate the effects of phase-dependent TMS during mu peak and trough phases on offline learning of a newly-acquired motor skill. MethodsOn Day 1, three groups of healthy adults practiced an explicit motor sequence learning task with their non-dominant left hand. After practice, phase-dependent TMS was applied to the right M1 during either mu peak or mu trough phases. The third group received sham TMS during random mu phases. On Day 2, all subjects were re-tested on the same task to evaluate offline learning. ResultsSubjects who received phase-dependent TMS during mu trough phases showed increased offline skill learning compared to those who received phase-dependent TMS during mu peak phases or sham TMS during random mu phases. Additionally, phase-dependent TMS during mu trough phases elicited stronger whole-brain broadband oscillatory power responses than phase-dependent TMS during mu peak phases. ConclusionsWe conclude that sensorimotor mu trough phases reflect brief windows of opportunity during which TMS can strengthen newly-acquired skill memories.
Highlights
The ability to transform new knowledge into long-lasting memories that guide future behavior is crucial in our daily lives
The main result of this study was that phase-dependent transcranial magnetic stimulation (TMS) during mu trough phases improved offline skill learning compared to phase-dependent TMS during mu peak phases and to sham TMS during random phases
Single neuron spiking rates are highest during mu trough phases and lowest during mu peak phases [12], and several recent studies have indicated that mu trough and peak phases reflect brief excitatory and inhibitory states within the human brain, respectively [13e15,17]
Summary
The ability to transform new knowledge into long-lasting memories that guide future behavior is crucial in our daily lives. Similar phenomena have been observed in the human brain: descending output from M1 to the spinal cord and inter-regional neuronal communication is increased during mu trough compared to peak phases [13e17]. Both the direction and magnitude of neuroplasticity induction within human M1 depends on sensorimotor mu phase, with LTP-like plasticity occurring preferentially during mu trough phases [13,18] and weak LTD-like plasticity occurring during mu peak phases [18]. Objective: To evaluate the effects of phase-dependent TMS during mu peak and trough phases on offline learning of a newly-acquired motor skill. Conclusions: We conclude that sensorimotor mu trough phases reflect brief windows of opportunity during which TMS can strengthen newly-acquired skill memories
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