Fatigue induces behavioural improvements in the unfatigued hand via altered functional connectivity and neurochemicals in cortical motor areas

Abstract

AbstractIn humans, motor learning is underpinned by changes in functional connectivity (FC) across the sensorimotor network. Unilateral exercise-induced fatigue increases FC in the ipsilateral primary motor cortex (M1) and supplementary motor area (SMA); areas involved in motor planning and execution of the contralateral hand. Unilateral fatiguing exercise is therefore a promising potential approach to augment motor performance in the non-fatigued, contralateral, hand. In a within-participant, controlled, randomized, cross-over design, 15 right-handed adults had two magnetic resonance imaging (MRI) sessions, where functional MRI and MR Spectroscopic Imaging were acquired before and after repeated right-hand contractions at either 5% or 50% maximum voluntary contraction (MVC). Before and after scanning, response times (RTs) were determined in both hands, and after scanning, participants performed a serial reaction time task (SRTT) with their left, unfatigued, hand. Nine minutes of 50% MVC contractions resulted in fatigue. This unimanual fatigue improved motor performance, as indexed by decreased RTs, in the contralateral hand. Although fatigue had no significant effects on sequence learning, fatigue led to a significant increase in the transfer of the learned skill to the untrained hand. These behavioural effects were supported by significant neural changes: an increase in SMA-SMA functional connectivity, and increased connectivity between right M1 and right Orbitofrontal Cortex. At a neurochemical level, the degree of fatigue-induced decrease in GABA in left M1, left and right SMA correlated with subsequent behavioural improvements in the left-hand. These results support unilateral fatiguing exercise as a potential therapeutic intervention in a range of neurological and orthopedic conditions.Key points summaryRight handgrip contractions at 50% MVC improve left hand response times.Repeated handgrip contractions at 50% MVC alter interhemispheric functional connectivity.Unilateral exercise may be an effective method for enhancing contralateral limb motor performance in rehabilitation settings.