Biology subjects

Greenhouse, I.

Publications and source records attributed to Greenhouse, I..

10 recordsLinked to original sources

bioRxiv2026

Motor automaticity in natural keyboard typing

Certain features of everyday motor skills become automatic while others remain controlled. Here we use a novel keyboard typing task to investigate whether motor automaticity depends on the frequency of naturally learned motor sequences. Participants type five-letter strings that vary in their word and bigram (two-letter sequence) frequency in natural language, allowing us to examine the influence of prior exposure without laboratory training. Novel pseudo word strings are tested as well. We find greater sequence frequency in natural language is associated with faster inter-keypress intervals and lower temporal variability within the sequence. In contrast, latencies to initiate a sequence are slower for novel pseudo-word strings but are otherwise insensitive to natural word frequency. We also find individual differences in inter-keypress speed and variability are robust across frequency levels but are unrelated to conventional measures of typing skill. Our method establishes keyboard typing as a scalable, ethologically valid framework for probing features of a naturally acquired human motor skill. This research will help extend laboratory-based studies of motor sequence learning and sets the stage for future investigations of linguo-motor processes. Moreover, our findings demonstrate which features within naturally acquired motor sequences become automatic and that typing proficiency is not determined solely by automaticity.

neuroscience↗

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

Interhemispheric inhibition between dorsal premotor and primary motor cortices is released during preparation of unimanual but not bimanual movements.

Previous research applying transcranial magnetic stimulation during unimanual reaction time tasks indicates a transient change in the inhibitory influence of dorsal premotor cortex over contralateral primary motor cortex shortly after the presentation of an imperative stimulus. Interhemispheric inhibition from the dorsal premotor cortex to the contralateral primary motor cortex shifts depending on whether the targeted effector representation in the primary motor cortex is selected for movement. Further, the timing of changes in inhibition covaries with the selection demands of the reaction time task. Less is known about modulation of dorsal premotor to primary motor cortex interhemispheric inhibition during the preparation of bimanual movements. In this study, we used a dual coil transcranial magnetic stimulation to measure dorsal premotor to primary motor cortex interhemispheric inhibition between both hemispheres during unimanual and bimanual simple reaction time trials. Interhemispheric inhibition was measured early and late in the "pre-movement period" (defined as the period immediately after the onset of the imperative stimulus and before the beginning of voluntary muscle activity). We discovered that interhemispheric inhibition was more facilitatory early in the pre-movement period compared to late in the pre-movement period during unimanual reaction time trials. In contrast, interhemispheric inhibition was unchanged throughout the pre-movement period during symmetrical bimanual reaction time trials. These results suggest that there is greater interaction between the dorsal premotor cortex and contralateral primary motor cortex during preparation of unimanual actions compared to bimanual actions.

neuroscience↗

bioRxiv2023

Early rise and persistent inhibition of electromyography during failed stopping

Reactively canceling movements is a vital feature of the motor system to ensure safety. This behavior can be studied in the laboratory using the stop signal task. There remains ambiguity about whether a "point-of-no-return" exists, after which a response cannot be aborted. A separate question concerns whether motor system inhibition associated with attempted stopping persists when stopping is unsuccessful. We address these two questions using electromyography (EMG) in two stop signal task experiments. Experiment 1 (n = 24) involved simple right and left index finger responses in separate task blocks. Experiment 2 (n = 28) involved a response choice between the right index and pinky fingers. To evaluate the approximate point-of-no-return, we measured EMG in responding fingers during the 100 ms preceding the stop signal and observed significantly greater EMG amplitudes during failed than successful stop trials in both experiments. Thus, EMG differentiated failed from successful stopping prior to the stop signal, regardless of whether there was a response choice. To address whether motor inhibition persists after failed stopping, we assessed EMG peak-to-offset durations and slopes (i.e., the rate of EMG decline) for go, failed stop, and successful stop (partial response EMG) trials. EMG peak-to-offset was shorter and steeper in failed stop trials compared to go and successful stop partial response EMG trials, suggesting motor inhibition persists even when failing to stop. These findings indicate EMG is sensitive to a point at which participants can no longer successfully stop an ongoing movement and suggest the peak-to-offset time of response-related EMG activity during failed stopping reflects stopping-related inhibition.

neuroscience↗

bioRxiv2020

Response preparation involves a release of intracortical inhibition in task-irrelevant muscles

Action preparation involves widespread modulation of motor system excitability, but the precise mechanisms are unknown. In this study, we investigated whether intracortical inhibition changes in task-irrelevant muscle representations during action preparation. We used transcranial magnetic stimulation (TMS) combined with electromyography in healthy human adults to measure motor evoked potentials (MEPs) and cortical silent periods (CSPs) in task-irrelevant muscles during the preparatory period of simple delayed response tasks. In Experiment 1, participants responded with the left-index finger in one task condition and the right-index finger in another task condition, while MEPs and CSPs were measured from the contralateral non-responding and tonically contracted index finger. During Experiment 2, participants responded with the right pinky finger while MEPs and CSPs were measured from the tonically contracted left-index finger. In both experiments, MEPs and CSPs were compared between the task preparatory period and a resting intertrial baseline. The CSP duration during response preparation decreased from baseline in every case. A laterality difference was also observed in Experiment 1, with a greater CSP reduction during the preparation of left finger responses compared to right finger responses. MEP amplitudes showed no modulation during movement preparation in any of the three response conditions. These findings indicate cortical inhibition associated with task-irrelevant muscles is transiently released during action preparation and implicate a novel mechanism for the controlled and coordinated release of motor cortex inhibition. New & NoteworthyIn this study we observed the first evidence of a release of intracortical inhibition in task-irrelevant muscle representations during response preparation. We applied transcranial magnetic stimulation to elicit cortical silent periods in task-irrelevant muscles during response preparation and observed a consistent decrease in the silent period duration relative to a resting baseline. These findings address the question of whether cortical mechanisms underlie widespread modulation in motor excitability during response preparation.

neuroscience↗

bioRxiv2020

A single mechanism for global and selective response inhibition under the influence of motor preparation

In our everyday behavior, we frequently cancel one movement while continuing others. Two competing models have been suggested for the cancellation of such specific actions: 1) the abrupt engagement of a unitary global inhibitory mechanism followed by reinitiation of the continuing actions, or 2) a balance between distinct global and selective inhibitory mechanisms. To evaluate these models, we examined behavioral and physiological markers of proactive control, motor preparation, and response inhibition using a combination of behavioral task performance measures, electromyography, electroencephalography, and motor evoked potentials elicited with transcranial magnetic stimulation. Healthy participants performed two versions of a stop signal task with cues incorporating proactive control: A unimanual task involving the initiation and inhibition of a single response, and a bimanual task involving the selective stopping of one of two prepared responses. Stopping latencies, motor evoked potentials, and frontal beta power (13-20 Hz) did not differ between the uni- and bimanual tasks. However, evidence for selective proactive control before stopping was manifest in the bimanual condition as changes in corticomotor excitability, mu (9-14 Hz), and beta (15-25 Hz) oscillations over sensorimotor cortex. Altogether, our results favor the recruitment of a single inhibitory stopping mechanism with the net behavioral output depending on the levels of action-specific motor preparation. Significance statementResponse inhibition is a core function of cognitive flexibility and movement control. Previous research has suggested separate mechanisms for selective and global inhibition, yet the evidence is inconclusive. Another line of research has examined the influence of preparation for action stopping, or what is called proactive control, on stopping performance, yet the neural mechanisms underlying this interaction are unknown. We combined transcranial magnetic stimulation, electroencephalography, electromyography and behavioral measures to compare selective and global inhibition models and to investigate markers of proactive control. The results favor a single inhibitory mechanism over separate selective and global mechanisms, but indicate a vital role for preceding motor activity in determining whether and which actions will be stopped.

neuroscience↗

bioRxiv2019

VETA: a Matlab toolbox for the collection and analysis of electromyography combined with transcranial magnetic stimulation

The combination of electromyography (EMG) and transcranial magnetic stimulation (TMS) offers a powerful non-invasive approach for investigating corticospinal excitability in both humans and animals. Acquiring and analyzing the data produced with this combination of tools requires overcoming multiple technical hurdles. Due in part to these technical hurdles, the field lacks standard routines for EMG data collection and analysis. This poses a problem for study replication and direct comparisons. Although software toolboxes already exist that perform either online EMG data visualization or offline analysis, there currently are no openly available toolboxes that flexibly perform both and also interface directly with peripheral EMG and TMS equipment. Here, we introduce Visualize EMG TMS Analyze (VETA), a MATLAB-based toolbox that supports simultaneous EMG data collection and visualization as well as automated offline processing and is specially tailored for use with motor TMS. The VETA toolbox enables the simultaneous recording of EMG, timed administration of TMS, and presentation of behavioral stimuli from a single computer. These tools also provide a streamlined analysis pipeline with interactive data visualization. Finally, VETA offers a standard EMG data format to facilitate data sharing and open science.

physiology↗

bioRxiv2019

Planning Face, Hand, and Leg Movements: Anatomical Constraints on Preparatory Inhibition.

Motor-evoked potentials (MEPs), elicited by Transcranial Magnetic Stimulation (TMS) over the motor cortex, are reduced during the preparatory period in delayed response tasks. Here we examine how MEP suppression varies as a function of the anatomical organization of the motor cortex. MEPs were recorded from a left index muscle while participants prepared a hand or leg movement in Experiment 1, or prepared an eye or mouth movement in Experiment 2. In this manner, we assessed if the level of MEP suppression in a hand muscle varied as a function of the anatomical distance between the agonist for the forthcoming movement and the muscle targeted by TMS. MEPs suppression was attenuated when the cued effector was anatomically distant from the hand (e.g., leg or facial movement compared to finger movement). A similar effect was observed in Experiment 3 in which MEPs were recorded from a muscle in the leg and the forthcoming movement involved the upper limb or face. These results demonstrate an important constraint on preparatory inhibition: It is sufficiently broad to be manifest in a muscle that is not involved in the task, but is not global, showing a marked attenuation when the agonist muscle belongs to a different segment of the body. New & NoteworthyUsing TMS, we examine changes in corticospinal excitability as people prepare to move. Consistent with previous work, we observe a reduction in excitability during the preparatory period, an effect observed in both task relevant and task irrelevant muscles. However, this preparatory inhibition is anatomically constrained, attenuated in muscles belonging to a different body segment than the agonist of the forthcoming movement.

neuroscience↗