Biology subjects

Wadsley, C. G.

Publications and source records attributed to Wadsley, C. G..

5 recordsLinked to original sources

bioRxiv2024

Goal-directed action preparation in humans entails a mixture of corticospinal neural computations

The seemingly effortless ability of humans to transition from thinking about actions to initiating them relies on sculpting corticospinal output from primary motor cortex. This study tested whether canonical additive and multiplicative neural computations, well-described in sensory systems, generalize to the corticospinal pathway during human action preparation. We used non-invasive brain stimulation to measure corticospinal input-output across varying action preparation contexts during instructed-delay finger response tasks. Goal-directed action preparation was marked by increased multiplicative gain of corticospinal projections to task-relevant muscles and additive suppression of corticospinal projections to non-selected and task-irrelevant muscles. Individuals who modulated corticospinal gain to a greater extent were faster to initiate prepared responses. Our findings provide physiological evidence of combined additive suppression and gain modulation in the human motor system. We propose these computations support action preparation by enhancing the contrast between selected motor representations and surrounding background activity to facilitate response selection and execution. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=108 SRC="FIGDIR/small/602530v4_figa1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@9f2444org.highwire.dtl.DTLVardef@5f6eforg.highwire.dtl.DTLVardef@196f41corg.highwire.dtl.DTLVardef@1746035_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOC_FLOATNO Goal-directed action preparation shapes corticospinal output across selected, nonselected, and task-irrelevant motor representations. This study examined whether additive and multiplicative neural computations, common in sensory systems, occur within the corticospinal pathway during action preparation. We probed corticospinal input-output during the performance of various instructed-delay response tasks by applying a range of transcranial magnetic stimulation (TMS) intensities (input) over the primary motor cortex and measuring the resultant motor-evoked potentials (output) from the hand. We found that goal-directed action preparation increases corticospinal gain multiplicatively in task-relevant motor representations while additively suppressing nonselected and irrelevant representations. Greater gain modulation predicted faster responses, highlighting how these computations can enhance signal-to-noise (SNR) to enable efficient action selection and execution in the human motor system. C_FIG Key pointsO_LINeural computations determine what information is transmitted through brain circuits. C_LIO_LIWe investigated whether the motor system uses computations similar to those observed in sensory systems by noninvasively stimulating the corticospinal pathway in humans during goal-directed action preparation. C_LIO_LIWe discovered physiological evidence that corticospinal projections to behaviorally relevant muscles exhibit nonlinear gain computations, while projections to behaviorally irrelevant muscles exhibit linear suppression. C_LIO_LIOur findings suggest that certain computational principles generalize to the human motor system and serve to enhance the contrast between relevant and background neural activity. C_LIO_LIThese results indicate that neural computations during goal-directed action preparation may support motor control by increasing signal-to-noise within the corticospinal pathway. C_LI

neuroscience↗

bioRxiv2024

Failed stopping transiently suppresses the electromyogram in task-irrelevant muscles

Selectively stopping individual parts of planned or ongoing movements is an everyday motor skill. For example, while walking in public you may stop yourself from waving at a stranger who you mistook for a friend while continuing to walk. Despite its ubiquity, our ability to selectively stop actions is limited. Canceling one action can delay the execution of other simultaneous actions. This stopping-interference effect on continuing actions during selective stopping may be attributed to a global inhibitory mechanism with widespread effects on the motor system. Previous studies have characterized a transient global reduction in corticomotor excitability by combining brain stimulation with electromyography (EMG). Here, we examined whether global motor inhibition during selective stopping can be measured peripherally and with high temporal resolution using EMG alone. Eighteen participants performed a bimanual anticipatory response inhibition task with their index fingers while maintaining a tonic contraction of the task-irrelevant abductor digiti minimi (ADM) muscles. A time series analysis of the ADM EMG signal revealed transient inhibition during failed stopping compared to go response trials 150 ms to 203 ms following the stop signal. The pattern was observed in both hands during bimanual stop-all trials as well as selective stop-left and stop-right trials of either hand. These results indicate that tonic muscle activity is sensitive to the effects of global motor suppression even when stopping fails. Therefore, EMG can provide a physiological marker of global motor inhibition to probe the time course and extent of stopping processes. Key PointsO_LISuccessfully stopping an initiated response globally suppresses the motor system. C_LIO_LIUsing electromyography of tonic muscle activity, we show inhibition spills over to task-irrelevant muscles during failed stopping. C_LIO_LIThe electromyographic pattern of inhibition is transient, lasting from approximately 150 to 203 ms following a stop signal when stopping fails. C_LIO_LIThe time course of the peripheral suppression of muscle activity may be leveraged to more precisely examine candidate neural mechanisms. C_LIO_LIThis non-invasive measure of motor system inhibition may be useful for tracking inhibitory control deficits in clinical populations. C_LI

neuroscience↗

bioRxiv2024

Corticospinal excitability at rest outside of a task does not differ from task intertrial intervals in healthy adults

Human corticospinal excitability modulates during movement, when muscles are active, but also at rest, when muscles are not active. These changes in resting motor system excitability can be transient or longer lasting. Evidence from transcranial magnetic stimulation (TMS) studies suggests even relatively short periods of motor learning on the order of minutes can have lasting effects on resting corticospinal excitability. Whether individuals are able to return corticospinal excitability to out-of-task resting levels during the intertrial intervals of behavioral tasks that do not include an intended motor learning component is an important question. Here, in twenty-six healthy young adults, we used single-pulse TMS and electromyography (EMG) to measure motor evoked potentials (MEPs) during two different resting contexts: 1) intertrial intervals of a choice-reaction time task, and 2) outside the task. In both contexts, five TMS intensities were used to evaluate possible differences in recruitment of corticospinal output. We hypothesized resting state excitability would be greater during intertrial intervals than out-of-task rest, reflected in larger MEP amplitudes. Contrary to our hypothesis, we observed no significant difference in MEP amplitudes between out-of-task rest and in-task intertrial intervals, and instead found evidence of equivalence, indicating that humans are able to return to a stable motor resting state within seconds after a response. These data support the interpretation that rest is a uniform motor state in the healthy nervous system. In the future, our data may be a useful reference for motor disorder populations with an impaired ability to return to rest.

neuroscience↗

bioRxiv2023

A global pause generates nonselective response inhibition during selective stopping

1Response inhibition is essential for terminating inappropriate actions. Selective response inhibition may be required when stopping part of a multicomponent action. However, a persistent response delay (stopping-interference effect) indicates nonselective response inhibition during selective stopping. This study aimed to elucidate whether nonselective response inhibition is the consequence of a global pause process during attentional capture or specific to a nonselective cancel process during selective stopping. We hypothesised that the stopping-interference effect would be larger in response to stop than ignore signals, owing to stronger nonselective response inhibition for explicit selective stopping. Twenty healthy human participants of either sex performed a bimanual anticipatory response inhibition paradigm with selective stop and ignore signals. Frontocentral and sensorimotor beta ({beta})-bursts were recorded with electroencephalography. Corticomotor excitability (CME) and short-interval intracortical inhibition (SICI) in primary motor cortex were recorded with transcranial magnetic stimulation. Behaviourally, responses in the non-signalled hand were delayed during selective ignore and stop trials. The response delay was largest during selective stop trials and indicated that the stopping-interference effect could not be attributed entirely to attentional capture. A stimulus-nonselective increase in frontocentral {beta}-bursts occurred during stop and ignore trials, whilst sensorimotor response inhibition was reflected in maintenance of {beta}-bursts and SICI relative to disinhibition observed during go trials. Signatures of response inhibition in the sensorimotor cortex contralateral to the responding hand were not associated with the magnitude of stopping-interference. Therefore, nonselective response inhibition during selective stopping results primarily from a nonselective pause process but does not entirely account for the stopping-interference effect. 2 Significance statementSelective stopping is a complex form of response inhibition where a person must execute and cancel part of an action at the same time. A stopping-interference effect exemplifies the complexity of selective stopping. The present study examined whether nonselective response inhibition during selective stopping results from a global pause during attentional capture or is specific to a deliberate cancel process. Behaviourally, the interference effect was larger during selective stop stimuli than selective ignore stimuli. However, neurophysiological signatures of nonselective response inhibition were elicited in response to both stop and ignore stimuli. These findings indicate that nonselective response inhibition during selective stopping results primarily from a nonselective pause process but does not entirely account for the stopping-interference effect.

neuroscience↗

bioRxiv2022

Proactive interhemispheric disinhibition supports response preparation during selective stopping

Response inhibition is essential for terminating inappropriate actions. A substantial delay may occur in the response of the non-stopped effector when only part of a multi-effector action is terminated. This stopping-interference effect has been attributed to nonselective response inhibition processes and can be reduced with proactive cueing. This study aimed to elucidate the role of interhemispheric primary motor cortex (M1-M1) influences during selective stopping with proactive cueing. We hypothesized that stopping-interference would be reduced as stopping certainty increased, owing to proactive recruitment of interhemispheric facilitation or interhemispheric inhibition when cued to respond or stop, respectively. Twenty-three healthy human participants performed a bimanual anticipatory response inhibition paradigm with cues signaling the likelihood of a stop-signal occurring. Dual-coil transcranial magnetic stimulation was used to determine corticomotor excitability (CME), interhemispheric inhibition (IHI), and interhemispheric facilitation (IHF) in the left hand at rest and during response preparation. Response times slowed and stopping-interference decreased with cues signaling increased stopping certainty. Proactive response inhibition was marked by a reduced rate of rise and faster cancel time in electromyographical bursts during stopping. There was a nonselective release of IHI but not CME from rest to in-task response preparation, while IHF was not observed in either context. An effector-specific CME but not IHF or IHI reduction was observed when the left hand was cued to stop. These findings indicate that the stopping-interference effect can be reduced through proactive suppression. Interhemispheric M1-M1 channels modulate inhibitory tone that supports responding, but not selective stopping, in a proactive response inhibition context. Significance statementResponse inhibition is essential for terminating inappropriate actions and, in some cases, may be required for only part of a multi-effector action. The present study examined interhemispheric influences between the primary motor cortices during selective stopping with proactive cueing. Stopping selectivity was greater with increased stopping certainty and marked by proactive response inhibition of the hand cued to stop. Inhibitory interhemispheric influences were released during response preparation but were not affected by proactive cueing. These findings indicate that between-hand stopping can be selective with proactive cueing, but cue-related improvements are unlikely to reflect advance engagement of interhemispheric influences between primary motor cortices.

neuroscience↗