Intracortical facilitation and inhibition in human primary motor cortex during motor skill acquisition

Abstract

The primary motor cortex (M1) is critical for movement execution, but its role in motor skill acquisition remains elusive. Here, we examine the role of M1 intracortical circuits during skill acquisition. Paired-pulse transcranial magnetic stimulation (TMS) paradigms of short-interval intracortical facilitation (SICF) and inhibition (SICI) were used to assess excitatory and inhibitory circuits, respectively. We hypothesised that intracortical facilitation and inhibition circuits in M1 would be modulated to support acquisition of a novel visuomotor skill. Twenty-two young, neurologically healthy adults trained with their nondominant hand on a skilled and non-skilled sequential visuomotor isometric finger abduction task. Electromyographic recordings were obtained from the nondominant first dorsal interosseous (FDI) muscle. Corticomotor excitability, SICF, and SICI were examined before, at the midway point, and after the 10-block motor training. SICI was assessed using adaptive threshold-hunting procedures. Task performance improved after the skilled, but not non-skilled, task training, which likely reflected the increase in movement speed during training. The amplitudes of late SICF peaks were modulated with skilled task training. There was no modulation of the early SICF peak, SICI, and corticomotor excitability with either task training. There was also no association between skill acquisition and SICF or SICI. The findings indicate that excitatory circuitries responsible for the generation of late SICF peaks, but not the early SICF peak, are modulated in motor skill acquisition for a sequential visuomotor isometric finger abduction task.

Investigating the effects of repetitive paired-pulse transcranial magnetic stimulation on visuomotor training using TMS-EEG

“…This has been supported by studies showing that priming-dependent modulation of motor learning is accompanied by related changes in motor cortical excitability (Ziemann et al ., 2004; Jung & Ziemann, 2009). Within the current study, visuomotor training resulted in improved skill levels that are consistent with previous work from our group (Opie et al ., 2020; Hand et al ., 2021; Hand et al ., 2023) and others (Reis et al ., 2009; Ho et al ., 2022). While skill was significantly greater in the iTMS+VT condition, examination of normalised data showed this stemmed from baseline differences in performance (see Results and Fig 3C).…”

Revisiting the Rotational Field TMS Method for Neurostimulation

“…The delicate motor functions and fine motor skills of the upper limbs include a complex interplay of inhibitory and excitatory inputs [40]. Hence, the combined activation of facilitatory neurons relevant to a certain hand muscle with relevant inhibitory neurons is expected to modulate motor response.…”