Biology subjects

McAllister, C. J.

Publications and source records attributed to McAllister, C. J..

3 recordsLinked to original sources

bioRxiv2023

Bilateral Intracortical Inhibition during Unilateral Motor Preparation and Sequence Learning

Motor sequence learning gradually quickens reaction time, suggesting that sequence learning alters motor preparation processes. Interestingly, evidence has shown that preparing sequence movements decreases short intracortical inhibition (SICI) in the contralateral motor cortex (M1), but also that sequence learning alters motor preparation processes in both the contralateral and ipsilateral M1s. Therefore, one possibility is that sequence learning alters the SICI decreases occurring during motor preparation in bilateral M1s. To examine this, two novel hypotheses were tested: unilateral sequence preparation would decrease SICI in bilateral M1s, and sequence learning would alter such bilateral SICI responses. Paired-pulse transcranial magnetic stimulation was delivered over the contralateral and ipsilateral M1s to assess SICI in an index finger muscle during the preparation of sequences initiated by either the right index or little finger. In the absence of sequence learning, SICI decreased in both the contralateral and ipsilateral M1s during the preparation of sequences initiated by the right index finger, suggesting that SICI decreases in bilateral M1s during unilateral motor preparation. As sequence learning progressed, SICI decreased in the contralateral M1 whilst it increased in the ipsilateral M1. Moreover, these bilateral SICI responses were observed at the onset of motor preparation, suggesting that sequence learning altered baseline SICI levels rather than the SICI decreases occurring during motor preparation per se. Altogether, these results suggest that SICI responses in bilateral M1s reflect two motor processes: an acute decrease of inhibition during motor preparation, and a cooperative but bidirectional shift of baseline inhibition levels as sequence learning progresses.

neuroscience↗

bioRxiv2023

Beta bursts correlate with synchronization of movements to rhythmic sounds

Accumulating evidence indicates transient beta bursts play an important role in the representation of temporal information and prediction. However, the role of beta bursts in sensorimotor synchronization (SMS) involving active interactions between motor and sensory systems to synchronize predictive movements to periodic events remains unclear. To answer this question, 15 participants were invited to complete a finger-tapping task whilst high-density EEG (128 channels) was recorded. Participants tapped with their right index finger in synchrony with 1 Hz and 0.5 Hz tone trains. In line with previous findings, we found a negative mean asynchrony between tone and tap time, i.e., taps preceded tones for both tone frequencies (1 and 0.5 Hz). In the EEG data, beta bursts were detected and their timing in relationship with tapping and auditory tracking was examined. Results revealed that beta bursts tracked tapping and were modulated by the low frequency phase of the tone frequency (i.e., 1 Hz or 0.5 Hz). Importantly, the locking of beta bursts to the phase of auditory tracking correlated with the behavioural variance on a single trial level that occurred while tapping to the tones. These results demonstrate a critical role for an interplay between beta bursts and low frequency phase in coordinating rhythmic behaviour.

neuroscience↗

bioRxiv2022

Dual-Coil Transcranial Magnetic Stimulation Reveals Temporal Dynamics of Bilateral Corticomotor Excitability During Response Inhibition

A changing environment may suddenly require some parts of a multi-component response to be cancelled, while others continue. Such partial cancellation consistently produces a behavioural delay in the remaining component. This delay may reflect a three-step process of non-selective neural inhibition of all response components, functional uncoupling of components, and selective initiation of the remaining response. However, most neurophysiological evidence supporting this hypothesis has been recorded from muscles of a single hand, without direct comparison between response components. We aimed to simultaneously record - and therefore directly compare - corticomotor excitability (CME) in the cancelled and responding hands using a dual-coil technique not yet applied in this context. Human participants received transcranial magnetic stimulation to both primary motor cortices 1ms apart while performing a bimanual response inhibition task. Motor evoked potentials (MEPs) were recorded from both first dorsal interosseous (FDI) muscles as a measure of CME during partial cancellation. An equivalent reduction in CME was evident for both the responding and cancelled FDI muscles 175 ms after the stop cue during successful partial cancellation. The responding FDI subsequently exhibited an increase in CME above levels in the cancelled hand, leading to the unimanual response. This study reveals, for the first time, the temporal dynamics of CME for both response components simultaneously during a bimanual response inhibition task. Our results provide strong evidence that neural modulation during sudden partial cancellation can be viewed in light of the stop-change framework as a sequential non-selective stop, uncouple and switch, then selectively go process.

neuroscience↗