Performance benefits conferred in the untrained limb after unilateral motor practice are termed cross-limb transfer. Although the effect is robust, the neural mechanisms remain incompletely understood. Here we use non-invasive brain stimulation to reveal that the neural adaptations that mediate motor learning in the trained limb are distinct from those that underlie cross-limb transfer to the opposite limb. Thirty-six participants practiced a ballistic motor task with their right index finger (150 trials), followed by intermittent-theta burst stimulation (iTBS) applied to the trained (contralateral) primary motor cortex (cM1 group), the untrained (ipsilateral) M1 (iM1 group), or the vertex (sham group). Following stimulation, another 150 training trials were undertaken. Motor performance and corticospinal excitability were assessed before motor training, pre- and post-iTBS, and following the second training bout. For all groups, training significantly increased performance and excitability of the trained hand, and performance, but not excitability, of the untrained hand, indicating transfer at the level of task performance. The typical faciltatory effect of iTBS on MEPs was reversed for cM1, suggesting homeostatic metaplasticity, and prior performance gains in the trained hand were degraded, suggesting that iTBS interfered with learning. In stark contrast, iM1 iTBS facilitated both performance and excitability for the untrained hand. Importantly, the effects of cM1 and iM1 iTBS on behaviour were exclusive to the hand contralateral to stimulation, suggesting that adaptations within the untrained M1 contribute to cross-limb transfer. However, the neural processes that mediate learning in the trained hemisphere versus transfer in the untrained hemisphere appear distinct.

Item Type:	Refereed Article
Keywords:	cross-limb transfer, ballistic motor learning, interlimb transfer, noninvasive brain stimulation, corticospinal excitability, motor performance
Research Division:	Health Sciences
Research Group:	Sports science and exercise
Research Field:	Motor control
Objective Division:	Health
Objective Group:	Other health
Objective Field:	Other health not elsewhere classified
UTAS Author:	Summers, JJ (Professor Jeffery Summers)
UTAS Author:	Hinder, MR (Associate Professor Mark Hinder)
ID Code:	109719
Year Published:	2016
Funding Support:	Australian Research Council (DE120100729)
Web of Science® Times Cited:	11
Deposited By:	Psychology
Deposited On:	2016-06-28
Last Modified:	2018-03-22
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