Abstract:
One feature that is a hallmark of complex human behaviour is learning to move
skilfully. Effective movement, which provides a means with which we interact with the external
world, relies on the acquisition of motor skills. The human nervous system demonstrates an
impressive capacity for acquiring, retaining, and refining novel motor skills over time owing to
its neuroplastic properties. Although motor skill acquisition constitutes a pivotal part of human
movement, the underlying neurophysiological mechanisms are poorly understood. Previous
literature suggests that motor skill acquisition may modulate excitatory and inhibitory networks
in the primary motor cortex (M1); interestingly, intracortical circuits that generate I-waves, a
series of high-frequency corticospinal volleys evoked by electrical or magnetic stimulation,
may be modulated by visuomotor learning. However, the link between motor skill acquisition
and intracortical function remains unclear.
The present study aimed to investigate how skill acquisition modulates intracortical
facilitation and inhibition in the M1. Twenty-two young, neurologically healthy adults (9 males,
mean age 23.4 ± 3.5, range 20–37) participated in a repeated-measures cross-over study
involving skilled and non-skilled motor training undertaken in a pseudorandomised order.
Skilled motor training involved a sequential visuomotor isometric finger abduction task with
high speed and accuracy demands. Non-skilled motor training involved a unitary version of the
task that required minimal speed and accuracy. Single- and paired-pulse transcranial magnetic
stimulation were performed before, during, and after the 10-block motor training. Short-interval
intracortical facilitation (SICF) and corticomotor excitability were assessed with a posterior-anterior induced current, and short-interval intracortical inhibition (SICI) using adaptive
threshold-hunting was assessed with an anterior-posterior induced current.
The protocols successfully elicited skill acquisition. There was modulation at the late
SICF peaks with skilled training. There were no changes to SICI or corticomotor excitability,
and no association between skill acquisition and SICF and SICI. The findings indicate that
excitatory M1 circuitries responsible for the generation of late I-waves are modulated in a motor
skill acquisition context and may allude to activation of inputs that influence excitatory M1
interneuronal circuits. This thesis informs our understanding of intracortical circuits that
participate in motor skill acquisition.