Biology subjects

MacDonald, H. J.

Publications and source records attributed to MacDonald, H. J..

4 recordsLinked to original sources

bioRxiv2026

Pre-Supplementary Motor Area Theta Burst Stimulation Alters Corticomotor Facilitation and Action Reinitiation Without Impairing Response Inhibition

BackgroundThe pre-supplementary motor area (preSMA) is increasingly being explored as a neuromodulation target for impulsive behaviour in several clinical populations. Treatment effects are generally interpreted as improvements in inhibitory control. However, healthy studies report improved/impaired/unchanged inhibitory control following identical preSMA stimulation protocols, and few studies examine accompanying neurophysiological changes. We therefore investigated whether preSMA stimulation influences downstream corticomotor excitability to modify a general stopping mechanism, other components of action control, or wider cue-dependent attentional processes relevant to impulsive behaviour. MethodsIn a preregistered, double-blind crossover study, 18 healthy adults received active and sham continuous theta burst stimulation (cTBS) over right preSMA. Motor-evoked potentials (MEPs), anticipatory response inhibition task measures, and alcohol dot-probe reaction times were collected before and after stimulation and analysed with linear mixed models. ResultsMEPs increased during sham (p = .028) but not after active cTBS (p = .741). Active cTBS did not affect complete or partial stopping on the response inhibition task. Instead, active cTBS slowed the continuing response after partial stopping (p < .001) whereas response execution sped up across the sham session (p < .001). No alcohol attentional bias or stimulation effect was detected. ConclusionsPreSMA cTBS did not impair general inhibitory or attentional control. Instead, it attenuated session-related corticomotor facilitation and selectively slowed reinitiation of a partially inhibited action. These findings suggest that clinical effects to impulsive behaviour from preSMA neuromodulation are primarily rooted in changes to motor preparation and action updating rather than a unitary stopping mechanism.

neuroscience↗

bioRxiv2025

β-bursting as a sensitive neural marker of inhibitory control in healthy older adults: a linear mixed-effects modelling and threshold-free cluster approach

Inhibitory control is essential for adaptive behaviour and declines with age, yet the underlying neural dynamics remain poorly understood. The {beta}-rhythm (15-29 Hz) is thought to reflect inhibitory signalling within the fronto-basal ganglia network. Recent evidence suggests that transient {beta}-bursts support inhibitory performance, often masked by conventional analyses of trial-averaged {beta}-power. To reveal the link between trial-by-trial {beta}-bursting and inhibition, we applied a recently developed analysis framework combining linear mixed-effects modelling (LMM) with threshold-free cluster enhancement (TFCE) during response inhibition and initiation in older adults. Twenty healthy older adults performed a bimanual anticipatory response inhibition task, while electroencephalography and electromyography were recorded to capture {beta}-activity ({beta}-burst rate/duration; averaged {beta}-power) and muscle bursting dynamics, respectively. Our analysis revealed distinct {beta}-bursting signatures absent in averaged {beta}-power data. Following the stop-signal, parieto-occipital {beta}-bursting presented before a temporal cascade from attentional to inhibitory processes. In addition to expected right fronto-central and bilateral sensorimotor activity, we observed left prefrontal {beta}-bursting, indexing broader inhibitory network engagement during bimanual response inhibition. Moreover, we established a functional link between right sensorimotor {beta}-bursting and muscle bursts during stopping, indicating rapid cortical suppression of initiated motor output. These results help clarify the mechanistic role of {beta}-oscillations and underscore the sensitivity of {beta}-bursting to both the timing and context of inhibitory demands in healthy older adults. Future research will help establish the potential of {beta}-bursting, combined with LMM-TFCE analysis, as a clinically relevant marker of impulse control dysfunction. Significance statementOur novel application of an advanced statistical framework revealed distinct spatiotemporal {beta}-bursting patterns during response inhibition and response withholding in healthy older adults, which were not captured by averaged {beta}-power. Identifying a further link between cortical {beta}-bursting and muscle-level suppression, the findings offer a mechanistic account of how the brain halts action in real time in older adults. This work provides a sensitive, trial-level framework for studying {beta}-bursting measures in general, as well as inhibitory control across aging and clinical populations.

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↗

bioRxiv2022

Exploring Stop Signal Reaction Time Over Two Sessions of the Anticipatory Response Inhibition Task

Various behavioural tasks can measure the motor component of impulse control, response inhibition. Response inhibition encompasses the ability to cancel unwanted actions and is evaluated via stop signal reaction time (SSRT). The current study explored the effect of two sessions on SSRT within the anticipatory response inhibition task (ARIT) and how this compared to the stop signal task (SST). Forty-four participants completed two sessions of the ARIT and SST, 24 hours apart. SSRT and its constituent measures (Go trial reaction time, stop signal delay) were calculated. SSRT reflecting non-selective inhibition was consistent between sessions in both tasks (both p > .293). Reaction time and stop signal delay also remained stable across sessions in the ARIT (all p > .063), whereas in the SST, both reaction time (p = .013) and stop signal delay (p = .009) increased. Across the two sessions, SSRT reflecting partial inhibition improved (p < .001), which was underpinned by changes to reaction time (p < .001) and stop signal delay (p < .001). The maximal efficiency of non-selective inhibition remained stable across two sessions in the ARIT. Results of the SST confirmed that non-selective inhibition can however be affected by more than inhibitory network integrity when Go trial reaction times are not constrained in task design. Partial response inhibition measures changed across sessions, suggesting the sequential process captured by the SSRT occurred more quickly in session two. These findings highlight the absence/extent of inherent SSRT changes possible during multiple-session study designs e.g., pre/post, or active/sham comparisons.

neuroscience↗