This work is supported by a Discovery Grant to BDC from the Natural Sciences and Engineering Research Council of Canada (NSERC; RGPIN 311680) and an Operating Grant to BDC from the Canadian Institutes of Health Research (CIHR; MOP-93796). RAK was supported by an Ontario Graduate Scholarship, and ALC was supported by an NSERC CREATE grant. The experimental apparatus described in this manuscript was supported by the Canada Foundation for Innovation. Additional support came from the Canada First Research Excellence Fund (BrainsCAN).

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The authors have nothing to disclose.

Humans have a remarkable capacity, when needed, to generate rapid, visually guided actions at latencies that approach minimal afferent and efferent conduction delays. We have previously described stimulus-locked responses (SLRs) on the upper limb as a new measure for rapid visuomotor responses6,9,10. While beneficial in providing a trial-by-trial benchmark for the first aspect of upper limb muscle recruitment influenced by the visual stimulus, limb SLRs have not been expressed in all subjects and often relied upon invasive intramuscular recordings. Here, an emerging target paradigm (Supplementary file 1) is described and the results are compared to those obtained with static targets. The benefits of the emergent target paradigm are apparent within individual participants, as participants who do not express the SLR in a static paradigm express one in the emerging target paradigm (e.g., Figure 2, participant 1- 1st row versus 2nd row). Furthermore, SLRs expressed in the emerging target paradigm are much larger than in other paradigms, sometimes attaining magnitudes that are equivalent to volitional magnitudes (Figure 2, participant 2; Figure 4, participant 5). Thus, this paradigm has proven to be effective in increasing the magnitude (Figure 3a), detectability of the SLR (Figure 3b), and promoting shorter reach RTs by ~50 ms (Figure 3b), compared to a paradigm using static targets. The emerging target paradigm also has advantages over paradigms requiring mid-flight corrections4, where a new stimulus is presented while a reaching movement is already in mid-flight. EMG or kinetic changes to movements already in mid-flight can also occur during experiments which change the visual feedback of current hand position, either alone or in conjunction with changes in target position13. While commonly used to study fast visuomotor responses, in such paradigms the EMG, kinetic, and/or kinematic activity driven in response to the new stimulus evolve on top of activity related to the original movement. In contrast, since the participant is in a stable posture at the time of stimulus emergence in the emerging target paradigm, SLRs are easily discerned, even on a trial-by-trial basis.
The three most critical aspects to the emerging target paradigm are the use of implied motion behind a barrier (3.1.3), certainty of the time of the target appearance (3.1.4), and full target emergence from behind an occluder (3.1.5). Of these three aspects, we speculate that the use of implied motion is the most important. Implied motion produces strong signals in motion-related areas in the dorsal visual stream that are indistinguishable from those produced by visible moving targets14. We speculate that, when combined with such implied motion, the sudden appearance of the emerging target below the obstacle creates a stronger visual transient than in the static target paradigm. Our implementation of the emerging target paradigm also incorporated a high degree of trial-by-trial certainty of the time at which the target would re-appear. The disappearance and subsequent emergence of the target behind the barrier may be akin to a &#8216;gap interval&#8217; between offset of a central fixation or hold stimulus and presentation of a peripheral target, which also expedites reach reaction times15 and promotes the expression of express saccades16, which are another type of fast visuomotor response. Finally, it is important that the target emerging from behind the barrier is presented in its entirety, rather than being presented as sliding from behind the barrier. Were the target to slide past the barrier, the earliest stimulus available to the visual system would be a &#8216;half-moon&#8217; stimulus that would lack the lower spatial frequencies known to promote earlier and stronger expression of limb SLRs10. In addition to these critical steps, it is important to position the outlets for the emerging targets at locations associated with the preferred or non-preferred direction of the muscle(s) under study. Introducing a background loading force to increase activity of the muscle of interest is also beneficial in the detection of limb SLRs.
In terms of troubleshooting, it is imperative to ensure that the time of target emergence is known on every trial, given the short latency of the limb SLR. This is particularly important for digital monitor displays, which may systematically induce variable delays in the time of stimulus presentation that could compromise accurate alignment of muscle activity to critical events. Prior to any implementation of the emerging target experiment, and regardless of the type of visual display, we encourage the use of multiple photodiodes to record the timing of stimulus appearance at multiple screen locations (e.g., at the unseen location referenced in 3.1.6, and at the locations where T1 will emerge). If the interval between stimulus appearance at these two locations is invariant across trials, then the photodiode at the unseen location can serve as a proxy for T1 appearance during the actual experiment, after adjusting for any lags specific to the different locations at which T1 may appear. We also encourage close &#8216;on-line&#8217; monitoring of EMG activity during the experiment, to watch for any changes in background EMG activity prior to target emergence, or to changes in EMG activity associated with reaching movements in of opposite from the muscle&#8217;s preferred direction of movement.
There are a number of ways in which the emerging target paradigm could be modified and doing so can further the understanding of the sensory, cognitive, and movement-related factors that influence the fast visuomotor system. Here, we instructed the subjects to prepare to move toward (a pro-reach) or away (an anti-reach) from the emerging target. As expected from previous results9, consolidation of this instruction enabled subjects to dampen SLR magnitude without changing SLR timing. This shows that the neural centers mediating the SLR can be pre-set by higher-order areas establishing task set, prior to target emergence. There are numerous other dimensions in which the task could be modified to manipulate cognitive factors, for example by altering the predictability of target appearance in either time (i.e., making the timing of emergence less predictable) or space (i.e., biasing target emergence to one side or another, or providing endogenous cues to indicate the side of emergence). Manipulations of the sensory parameters of the emerging target (e.g., the speed, contrast, size, or color of the emerging stimulus, or the presence of competing distractors) will also provide insights into underlying substrates. Presenting a static rather than moving target below the barrier would also help parse the effects of target motion versus temporal predictability on the robustness of the limb SLR. Finally, from a motor perspective, the framework of the emerging target paradigm can be extended to bilateral reaching movements and establishing the presence of robust SLRs on upper limb muscles potentiates the investigation the distribution of such signals to other trunk or limb muscles.
One of the limitations associated with this paradigm, perhaps paradoxically, is the degree to which reach RTs were shortened. Our SLR detection criteria resembled that used previously12, as we ran separate time-series ROC analyses for the shorter- or longer-than median RT groups. Doing so requires some degree of variance in reach RTs, and in practice we have found that reach RTs are shorter and less variable in the emerging target paradigm compared to the static paradigm (279 +/- 58 ms (static); 207 +/- 34 ms (emerging target)). Indeed, RTs were sometimes shortened to such a degree that the movement-related volley of EMG activity often blended into the SLR interval. Consequently, the time-series ROC often rose directly from values near 0.5 to values near 1.0, without displaying the brief decrease after the SLR that was required for detection in ref.8 (see Figure 4, participant 1,2,4,5). More importantly, the smaller RT variance is detrimental to the detection of slope (Figure 1c); whereby a lack of variability in RTs may lead to lower levels of detectable SLRs. We expect that the detection criteria for SLRs may continue to evolve and will likely have to be optimized to the specifics of the task at hand. Other task manipulations, perhaps by increasing the temporal uncertainty of target re-emergence or requiring that subjects wait to move for a short interval after target emergence (e.g., by waiting for the emerged target to change color), may help increase the mean and variance of reach RTs and separate recruitment during the SLR interval from that associated with movement onset. A second limitation, which has not been explored, may be that some participants may not exhibit an SLR in the emerging target paradigm. We recognize that our sample is small and future studies should employ the emerging target paradigm on larger populations.
In closing, the emerging target paradigm offers a more reliable technique for eliciting the SLR, when compared to paradigms using static targets. The framework of the emerging target paradigm will advance the study of rapid visuomotor responses, by providing a means to obtain robust expression of upper limb SLRs. It is particularly noteworthy that all of the results reported here were obtained with surface recordings, as this will enable study of SLRs in populations that may be less amenable to intramuscular recording, like the young, the elderly, or the infirm. We also expect that the emerging target paradigm could be extended into animal studies in non-human primates and combined with neurophysiological techniques to explore potential neural substrates. Together with future work in humans that can rapidly explore the numerous sensory, cognitive, and motor dimensions of the task, the emerging target paradigm should potentiate hypothesis-driven explorations of the fast visuomotor system.

When we notice a message on our cellphone, we are prompted to perform a visually guided reach to pick up our phone and read the message. Visual features such as the shape and size of the phone are transformed into motor commands allowing us to successfully reach the goal. Such visuomotor transformations may be studied in laboratory conditions, which permit a high degree of control. However, there are scenarios where response time is important, e.g., catching the phone if it were to fall. Laboratory studies of fast visuomotor behaviors often rely on displaced target paradigms where on-going movements are modified in mid-flight following some change in target position (e.g., see ref.1,2). While such online corrections can occur in &#60;150 ms3, it is difficult to ascertain the exact timing of fast visuomotor output using kinematics alone due to the low-pass filtering characteristics of the arm, and because fast visuomotor output supersedes a movement already in mid-flight. Such complications lead to uncertainty about the substrates underlying fast visuomotor responses (see ref.4 for review). Some studies suggest that subcortical structures such as the superior colliculus, rather than fronto-parietal cortical areas, may initiate online corrections5.
This uncertainty regarding the underlying neural substrates may be due, at least in part, to the lack of a reliable biomarker for the output of the fast visuomotor system. Recently, we have described a measure of fast visuomotor responses that may be generated from static postures and recorded via electromyography (EMG). Stimulus-locked responses (SLRs) are time locked bursts of EMG activity that precede voluntary movement6,7, evolving consistently ~100 ms after stimulus onset. As the name implies, SLRs are evoked by stimulus onset, persisting even if an eventual movement is withheld8 or moves in the opposite direction9. Furthermore, SLRs evoked by target displacement in a dynamic paradigm are associated with shorter latency online corrections10. Thus, SLRs provide an objective measure to systematically study the output of a fast visuomotor system involved in short latency RTs, as they may be generated from a static posture and parsed from other EMG signals unrelated to the initial phase of the fast visuomotor response.
The goal of the current study is to present a visually-guided reaching paradigm that robustly elicits SLRs. Previous studies investigating the SLR have reported less than 100% detection rates across participants, even when using more invasive intramuscular recordings6,8,9. Low detection rates and a reliance on invasive recordings limit the usefulness of SLR measures in future investigations into the fast visuomotor system in disease or across the lifespan. While some subjects may simply not express SLRs, the stimuli and behavioral paradigms used previously may not have been ideal to evoke the SLR. Past reports of SLRs have typically used paradigms wherein participants generate visually-guided reaches towards static, suddenly appearing targets6,9. However, a fast visuomotor system is the most likely needed in scenarios where one must rapidly interact with a falling or flying object, leading one&#160;to wonder if moving rather than static stimuli may better evoke SLRs. Therefore, we have adapted a moving target paradigm used to study eye movements11, and combined it with a pro/anti visually guided reaching task used to examine the SLR9. When compared to results from paradigms used previously6,8,9, it was found that SLRs in the emerging target paradigm evolved sooner, attained higher magnitudes, and were more prevalent across our participant sample. Overall, the emerging target paradigm promotes the expression of fast visuomotor responses to such a degree that objective EMG measures can be made reliably with surface recordings, potentiating study within clinical populations and across the lifespan. Further, the emerging target paradigm can be modified in many different ways, promoting more thorough investigations into the sensory, cognitive, and motor factors that promote or modify fast visuomotor responses.

<table><tbody><tr><td>Bagnoli-8 Desktop Surface EMG System</td><td>Delsys Inc.</td><td></td><td>Another reaching apparatus may be used</td></tr><tr><td>Kinarm End-Point Robot</td><td>Kinarm, Kingston, Ontario, Canada</td><td></td><td>Another reaching apparatus may be used</td></tr><tr><td>MATLAB (version R2016a) Stateflow and Simulink applications</td><td>The MathWorks, Inc., Natick, Massachusetts, United States</td><td></td><td></td></tr><tr><td>PROPixx projector</td><td>VPIXX Saint-Bruno, QC, Canada</td><td></td><td>This is a custom built addon for the Kinarm. Other displays may be used. Resolution: 1920 x 1080. Standard viewing monitors may also be used.</td></tr></tbody></table>

an emerging target paradigm to evoke fast visuomotor responses on human upper limb muscles

To reach towards a seen object, visual information has to be transformed into motor commands. Visual information such as the object&#8217;s color, shape, and size are processed and integrated within numerous brain areas, then ultimately relayed to the motor periphery. In some instances, a reaction is needed as fast as possible. These fast visuomotor transformations, and their underlying neurological substrates, are poorly understood in humans as they have lacked a reliable biomarker. Stimulus-locked responses (SLRs) are short latency (&#60;100 ms) bursts of electromyographic (EMG) activity representing the first wave of muscle recruitment influenced by visual stimulus presentation. SLRs provide a quantifiable output of rapid visuomotor transformations, but SLRs have not been consistently observed in all subjects in past studies. Here we describe a new, behavioral paradigm featuring the sudden emergence of a moving target below an obstacle that consistently evokes robust SLRs. Human participants generated visually guided reaches toward or away from the emerging target using a robotic manipulandum while surface electrodes recorded EMG activity from the pectoralis major muscle. In comparison to previous studies that investigated SLRs using static stimuli, the SLRs evoked with this emerging target paradigm were larger, evolved earlier, and were present in all participants. Reach reaction times (RTs) were also expedited in the emerging target paradigm. This paradigm affords numerous opportunities for modification that could permit systematic study of the impact of various sensory, cognitive, and motor manipulations on fast visuomotor responses. Overall, our results demonstrate that an emerging target paradigm is capable of consistently and robustly evoking activity within a fast visuomotor system.

Stimulus locked responses (SLRs) are brief bursts of muscle activity time locked to the stimulus onset that evolve well before the larger volley of muscle recruitment associated with movement onset. The time-locked nature of the SLR produced a &#8216;banding&#8217; of muscle activity visible at ~100 ms when viewing all trials sorted for reaction time (RT) (Figure 1a, highlighted by grey boxes). As shown in Figure 1a, SLRs was dependent on target location, with SLRs on the right pectoralis major consisting of an increase or decrease in muscle recruitment following leftward or rightward target presentation, respectively. SLRs were detected with an RT split analysis (methods 4.1.4), whereby separate time-series ROC analyses were performed on early and late RT trials (Figure 1b- purple versus green). This analysis indicates whether EMG onset was invariant to stimulus or movement onset, which was determined by the slope of the line connecting early and late discrimination times plotted as a function of RT (Figure 1c). Previous studies of the SLR using static stimuli reported detection rates across all participants below 70%8,9. Here, a comparison was made to the effectiveness of an emerging target paradigm in evoking SLRs to that obtained using a paradigm with static targets.
In the emerging target paradigm (Supplemental Figure 1), subjects reached towards emerging moving targets instead of stationary targets. Figure 2 shows data from two subjects reaching toward a stationary target (first and third rows) or moving targets that emerge beneath an occluder (second and fourth rows). Participant 1 does not exhibit an SLR in the static paradigm, but exhibits a clear SLR in the emerging target paradigm; SLRs were apparent as a vertical band of activity in the trial-by-trial plots (Figure 2a) ~100 ms after stimulus onset in the emerging target but not static paradigm. The SLR was also apparent in the mean EMG traces (Figure 2b) for participant 1 in the emerging target but not static paradigm (red traces in top two rows of Figure 2b). Participant 1 provided an example of someone who does not exhibit an SLR in a static paradigm used previously in the literature, but who does exhibit an SLR in the emerging target paradigm. In contrast, while participant 2 exhibited an SLR in both the static and emerging target paradigms, the magnitude of the SLR was much greater in the emerging target paradigm, with magnitudes approaching that attained just before movement onset.
We compared the properties of the SLRs observed in the emerging targets versus static paradigm across the sample, examining data collected in the pro-reach condition. As shown in Figure 3a (green lines), and consistent with the representative results in Figure 2, SLR magnitude was considerably larger in the emerging target versus static paradigm, with recruitment magnitudes in the interval 80-120 ms after stimulus onset increasing fivefold on average. In contrast to such systematic changes in SLR magnitude, the latency of detected SLRs did not differ in the static versus emerging target paradigm (Figure 3a, purple lines). As shown in Figure 3b (blue bars), SLRs was detected in all five participants in the emerging target paradigm (i.e., a prevalence of 100%), but only in three participants in a paradigm with static targets (i.e., a prevalence of 60%, resembling previous reports8,9). Observing SLRs on all participants in the emerging target paradigm was even more impressive considering that we relied on non-invasive surface EMG recordings, whereas previous reports have generally relied on invasive intramuscular EMG recordings. Importantly, while reach RTs tended to be much shorter in the emerging target versus static paradigm (Figure 3b, black lines), SLRs do not simply arise in the emerging target paradigm due to expedited RTs. For example, the data for Participant 1 in Figure 2 exhibited prominent SLRs in the emerging target but not static paradigm for overlapping ranges of reach RTs. Finally, we also examined how the instruction to move away from the emerging target influenced the SLRs. As found previously with static targets9, SLR magnitudes in the anti-reach condition were muted compared to that in the pro-reach condition (Figure 3c, blue lines; see also mean EMG traces in Figure 2, Figure 4). This shows that emerging target paradigm can be used to study aspects of cognitive control, which in this case related to consolidation of the instruction to move either toward or away from an emerging target.
We show data recorded from all five participants in Figure 4, in order to illustrate the variability in the characteristics of SLRs recorded in the static versus emerging target paradigms in the pro- and anti-reach conditions (the grey boxes in Figure 4 depict the SLR interval). As with participant 1 (shown in upper two rows in Figure 2), participant 5 also exhibited an SLR in the emerging target but not static paradigm in the pro-reach condition. As with participant 2 (shown in lower two rows in Figure 2), participants 3 and 4 also exhibited considerably larger SLRs in the emerging target versus static paradigms in the pro-reach condition. Two other features of the data shown in Figure 4 deserve emphasis. First, in participants 3, 4 and 5, we observed a larger SLR in the anti-reach variant of the emerging target task, with the time-series ROC peaking above 0.6 before assuming levels near 0. An SLR toward the stimulus in an anti-reach condition has been observed previously9, and we have related this to the brief movement of the hand toward the stimulus in an anti-reach variant of an on-line correction task3. Second, in the pro-reach condition in the emerging target task, a distinct separation was observed between the SLR and ensuing movement-aligned activity in some participants (e.g., participants 1, 3 and 5; see how time-series ROC drops briefly after peaking during the SLR interval), but found that the SLR blended into movement-aligned activity in others (e.g., participants 2 and 4). As noted below, this relates to the design of algorithms for detecting the SLR.
Overall, the emerging target paradigm is more effective at evoking SLRs and short RTs than paradigms using static targets. This is demonstrated by increases in SLR prevalence, magnitude, and shorter latency RTs with respect to static targets.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61428/61428fig01.jpg" /> 
Figure 1: SLR detection.&#160;Example of an SLR from a representative participant, illustrating the detection criteria for SLRs. (a) Trial-by-trial recruitment for right pectoralis major muscle for right or left reaches in the pro-reach condition. Each row is a different trial. Intensity of color conveys the magnitude of EMG activity. Trials were sorted by reach RT (white boxes) and aligned to stimulus onset (black line). The SLR appeared as a vertical banding of activity highlighted by grey boxes; note how EMG activity increased or decreased (time-locked ~90 ms) after leftward or rightward stimulus presentation, respectively. Purple or green bars indicate the trials contributing to the early or late RT groups, respectively. (b) Time-series ROC analysis indicating time of EMG discrimination for early (purple) and late (green) trials shown in (a). (c) For the early (purple) and late (green) groups, mean RT was plotted as a function of ROC discrimination. The slope of the line connecting these two points is 83.7&#730;, indicating that EMG activity was more aligned to stimulus presentation than movement onset. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61428/61428fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61428/61428fig02.jpg" /> 
Figure 2: Representative results.&#160;Data from participants 1 and 2 showing the variability in the presence or absence or SLRs in the static (1st and 3rd rows), and the consistency of SLR presence in the emerging target paradigms (2nd and 4th rows). (a) Trial-by-trial recruitment for right pectoralis major muscle for these participants (same format as Figure 1a). Conditions exhibiting an SLR are outlined in purple (2nd, 3rd and 4th rows). (b) Mean +/- SE of EMG activity for both pro (red) and anti (blue) reaches, segregated by the side of stimulus presentation (fainter traces used for movements in the non-preferred direction). (c) Time-series ROC analysis for pro (red) and anti (blue) reaches shown in (b). SLR epoch highlighted in grey box; horizontal dashed lines at 0.4 and 0.6. Vertical colored lines (if present in pro condition) show the discrimination time for pro- (red) or anti- (blue) reach trials. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61428/61428fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61428/61428fig03.jpg" /> 
Figure 3: Effects of an emerging target paradigm on SLR characteristics and reach RT.&#160;(a) SLR latency (purple) and magnitude (green) for pro reaches in static versus emerging target paradigms. Latency defined as first 8 out of 10 continuous data points surpassing ROC threshold of 0.6 (see methods). Magnitude of SLR was defined as the integrated area over 30 ms after SLR discrimination between the mean EMG activity on left versus right trials. All magnitudes were normalized to the maximum for the participant across conditions (e.g., a value of 1 indicates the maximal response). (b) SLR prevalence and reach RT. (c) SLR magnitude and latency results from pro and anti-reaches in the emerging target paradigm. * denotes significance at p&#60;.05 compared to static or anti condition based on unpaired t-test. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61428/61428fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61428/61428fig04.jpg" /> 
Figure 4: Mean EMG and time-series ROC analyses for all participants.&#160;Left column of plots: Mean +/- SE of EMG activity for both pro (red) and anti (blue) reaches, segregated by the side of stimulus presentation (fainter traces used for movements in the non-preferred direction). Right column of plots: Time-series ROC analysis for pro (red) and anti (blue) reaches shown in (left column of plots). SLR epoch highlighted in grey box; horizontal dashed lines at 0.4 and 0.6. Vertical colored lines (if present in pro condition) show the discrimination time for pro- (red) or anti- (blue) reach trials. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61428/61428fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Supplementary Figure 1: Top view of task in the robotic reaching device. Large white dot on lower left side represents the photodiode. White target (T1) is shown exiting the inverted &#8216;y&#8217; path to the left. White dot to the right of T1 represents RTC in the midst of a visually guided reach. The occluder is shown here as green, indicating a pro reach was required. T0 not shown, due to the simultaneous disappearance with target emergence. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61428/61428supfig01.jpg" target="_blank">Please click here to download this figure.</a>

Watch this Scientific Journal Video about An Emerging Target Paradigm to Evoke Fast Visuomotor Responses on Human Upper Limb Muscles at JoVE.com

An Emerging Target Paradigm to Evoke Fast Visuomotor Responses on Human Upper Limb Muscles

Presented here is a behavioral paradigm that elicits robust fast visuomotor responses on human upper limb muscles during visually guided reaches.

To reach towards a seen object, visual information has to be transformed into motor commands. Visual information such as the object&#8217;s color, shape, ...

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Nanyang Technological University

Research

JoVE Journal

Neuroscience

4.2K Views.  Western University. Hier gepresenteerd is een gedragskundig paradigma dat robuuste snelle visuomotorische reacties op menselijke bovenste ledematen spieren tijdens visueel geleide bereikt elicits.

Video: An Emerging Target Paradigm to Evoke Fast Visuomotor Responses on Human Upper Limb Muscles

Corticospinal Excitability Modulation During Action Observation

This study used the transcranial magnetic stimulation/motor evoked potential (TMS/MEP) technique to pinpoint when the automatic tendency to mirror someone else's action becomes anticipatory simulation of a complementary act. TMS was delivered to the left primary motor cortex corresponding to the hand to induce the highest level of MEP activity from the abductor digiti minimi (ADM; the muscle serving little finger abduction) as well as the first dorsal interosseus (FDI; the muscle serving index finger flexion/extension) muscles. A neuronavigation system was used to maintain the position of the TMS coil, and electromyographic (EMG) activity was recorded from the right ADM and FDI muscles. Producing original data with regard to motor resonance, the combined TMS/MEP technique has taken research on the perception-action coupling mechanism a step further. Specifically, it has answered the questions of how and when observing another person's actions produces motor facilitation in an onlooker's corresponding muscles and in what way corticospinal excitability is modulated in social contexts.

Single-pulse transcranial magnetic stimulation over the primary motor cortex, neuronavigation, and registration of electromyographic activity of hand muscles were used in this study to explore corticospinal excitability while participants were observing action sequences.

This study used the transcranial magnetic stimulation/motor evoked potential (TMS/MEP) technique to pinpoint when the automatic tendency to mirror someone ...

Behavior

Methods to Explore the Influence of Top-down Visual Processes on Motor Behavior

Kinesthetic awareness is important to successfully navigate the environment. When we interact with our daily surroundings, some aspects of movement are deliberately planned, while others spontaneously occur below conscious awareness. The deliberate component of this dichotomy has been studied extensively in several contexts, while the spontaneous component remains largely under-explored. Moreover, how perceptual processes modulate these movement classes is still unclear. In particular, a currently debated issue is whether the visuomotor system is governed by the spatial percept produced by a visual illusion or whether it is not affected by the illusion and is governed instead by the veridical percept. Bistable percepts such as 3D depth inversion illusions (DIIs) provide an excellent context to study such interactions and balance, particularly when used in combination with reach-to-grasp movements. In this study, a methodology is developed that uses a DII to clarify the role of top-down processes on motor action, particularly exploring how reaches toward a target on a DII are affected in both deliberate and spontaneous movement domains.

It is unclear how top-down signals from the ventral visual stream affect movement. We developed a paradigm to test motor behavior towards a target on a 3D depth inversion illusion. Significant differences are reported in both deliberate, goal-directed movements and automatic actions under illusory and veridical viewing conditions.

Kinesthetic awareness is important to successfully navigate the environment. When we interact with our daily surroundings, some aspects of movement are ...

Functional Near Infrared Spectroscopy of the Sensory and Motor Brain Regions with Simultaneous Kinematic and EMG Monitoring During Motor Tasks

There are several advantages that functional near-infrared spectroscopy (fNIRS) presents in the study of the neural control of human movement. It is relatively flexible with respect to participant positioning and allows for some head movements during tasks. Additionally, it is inexpensive, light weight, and portable, with very few contraindications to its use. This presents a unique opportunity to study functional brain activity during motor tasks in individuals who are typically developing, as well as those with movement disorders, such as cerebral palsy. An additional consideration when studying movement disorders, however, is the quality of actual movements performed and the potential for additional, unintended movements. Therefore, concurrent monitoring of both blood flow changes in the brain and actual movements of the body during testing is required for appropriate interpretation of fNIRS results. Here, we show a protocol for the combination of fNIRS with muscle and kinematic monitoring during motor tasks. We explore gait, a unilateral multi-joint movement (cycling), and two unilateral single-joint movements (isolated ankle dorsiflexion, and isolated hand squeezing). The techniques presented can be useful in studying both typical and atypical motor control, and can be modified to investigate a broad range of tasks and scientific questions.

Monitoring brain activity during upright motor tasks is of great value when investigating the neural source of movement disorders. Here, we demonstrate a protocol that combines functional near infrared spectroscopy with continuous monitoring of muscle and kinematic activity during 4 types of motor tasks.

There are several advantages that functional near-infrared spectroscopy (fNIRS) presents in the study of the neural control of human movement. It is ...

Multifunctional Setup for Studying Human Motor Control Using Transcranial Magnetic Stimulation, Electromyography, Motion Capture, and Virtual Reality

The study of neuromuscular control of movement in humans is accomplished with numerous technologies. Non-invasive methods for investigating neuromuscular function include transcranial magnetic stimulation, electromyography, and three-dimensional motion capture. The advent of readily available and cost-effective virtual reality solutions has expanded the capabilities of researchers in recreating &#8220;real-world&#8221; environments and movements in a laboratory setting. Naturalistic movement analysis will not only garner a greater understanding of motor control in healthy individuals, but also permit the design of experiments and rehabilitation strategies that target specific motor impairments (e.g. stroke). The combined use of these tools will lead to increasingly deeper understanding of neural mechanisms of motor control. A key requirement when combining these data acquisition systems is fine temporal correspondence between the various data streams. This protocol describes a multifunctional system&#8217;s overall connectivity, intersystem signaling, and the temporal synchronization of recorded data. Synchronization of the component systems is primarily accomplished through the use of a customizable circuit, readily made with off the shelf components and minimal electronics assembly skills.

Transcranial magnetic stimulation, electromyography, and 3D motion capture are commonly used non-invasive techniques for investigating neuromuscular function in humans. In this paper, we describe a protocol that synchronously samples data generated by all three of these tools along with the unique addition of virtual reality stimulus presentation and feedback.

The study of neuromuscular control of movement in humans is accomplished with numerous technologies. Non-invasive methods for investigating neuromuscular ...

Event-related Potentials During Target-response Tasks to Study Cognitive Processes of Upper Limb Use in Children with Unilateral Cerebral Palsy

Unilateral Cerebral Palsy (CP) is a neurodevelopmental disorder that is a very common cause of disability in childhood. It is characterized by unilateral motor impairments that are frequently dominated in the upper limb. In addition to a reduced movement capacity of the affected upper limb, several children with unilateral CP show a reduced awareness of the remaining movement capacity of that limb. This phenomenon of disregarding the preserved capacity of the affected upper limb is regularly referred to as Developmental Disregard (DD). Different theories have been postulated to explain DD, each suggesting slightly different guidelines for therapy. Still, cognitive processes that might additionally contribute to DD in children with unilateral CP have never been directly studied. The current protocol was developed to study cognitive aspects involved in upper limb control in children with unilateral CP with and without DD. This was done by recording event-related potentials (ERPs) extracted from the ongoing EEG during target-response tasks asking for a hand-movement response. ERPs consist of several components, each of them associated with a well-defined cognitive process (e.g., the N1 with early attention processes, the N2 with cognitive control and the P3 with cognitive load and mental effort). Due to its excellent temporal resolution, the ERP technique enables to study several covert cognitive processes preceding overt motor responses and thus allows insight into the cognitive processes that might contribute to the phenomenon of DD. Using this protocol adds a new level of explanation to existing behavioral studies and opens new avenues to the broader implementation of research on cognitive aspects of developmental movement restrictions in children.

Several children with unilateral Cerebral Palsy seem to disregard the preserved capacity of their affected upper limb. This Developmental Disregard is extensively described in the literature but the involved cognitive processes have not been studied. To study underlying cognitive factors of upper limb control, an event-related potential protocol was developed.

Unilateral Cerebral Palsy (CP) is a neurodevelopmental disorder that is a very common cause of disability in childhood. It is characterized by unilateral ...

Combining Multiple Data Acquisition Systems to Study Corticospinal Output and Multi-segment Biomechanics

Transcranial magnetic stimulation techniques allow for an in-depth investigation into the neural mechanisms that underpin human behavior. To date, the use of TMS to study human movement, has been limited by the challenges related to precisely timing the delivery of TMS to features of the unfolding movement and, also, by accurately characterizing kinematics and kinetics. To overcome these technical challenges, TMS delivery and acquisition systems should be integrated with an online motion tracking system. The present manuscript details technical innovations that integrate multiple acquisition systems to facilitate and advance the use of TMS to study human movement. Using commercially available software and hardware systems, a step-by-step approach to both the hardware assembly and the software scripts necessary to perform TMS studies triggered by specific features of a movement is provided. The approach is focused on the study of upper limb, planar, multi-joint reaching movements. However, the same integrative system is amenable to a multitude of sophisticated studies of human motor control.

The use of transcranial magnetic stimulation (TMS) to study human motor control requires the integration of data acquisition systems to control TMS delivery and simultaneously record human behavior. The present manuscript provides a detailed methodology for integrating data acquisition systems for the purpose of investigating human movement via TMS.

Transcranial magnetic stimulation techniques allow for an in-depth investigation into the neural mechanisms that underpin human behavior. To date, the use ...

Design and Use of an Apparatus for Presenting Graspable Objects in 3D Workspace

Reaching and grasping are highly-coupled movements, and their underlying neural dynamics have been widely studied in the last decade. To distinguish reaching and grasping encodings, it is essential to present different object identities independent of their positions. Presented here is the design of an automatic apparatus that is assembled with a turning table and three-dimensional (3D) translational device to achieve this goal. The turning table switches different objects corresponding to different grip types while the 3D translational device transports the turning table in 3D space. Both are driven independently by motors so that the target position and object are combined arbitrarily. Meanwhile, wrist trajectory and grip types are recorded via the motion capture system and touch sensors, respectively. Furthermore, representative results that demonstrate successfully trained monkey using this system are described. It is expected that this apparatus will facilitate researchers to study kinematics, neural principles, and brain-machine interfaces related to upper limb function.

Presented here is a protocol to build an automatic apparatus that guides a monkey to perform the flexible reach-to-grasp task. The apparatus combines a 3D translational device and turning table to present multiple objects in an arbitrary position in 3D space.

Reaching and grasping are highly-coupled movements, and their underlying neural dynamics have been widely studied in the last decade. To distinguish ...

A Modified Lean and Release Technique to Emphasize Response Inhibition and Action Selection in Reactive Balance

Assessment of reactive balance traditionally imposes some type of perturbation to upright stance or gait followed by measurement of the resultant corrective behavior. These measures include muscle responses, limb movements, ground reaction forces, and even direct neurophysiological measures such as electroencephalography. Using this approach, researchers and clinicians can infer some basic principles regarding how the nervous system controls balance to avoid a fall. One limitation with the way in which these assessments are currently used is that they heavily emphasize reflexive actions without any need to revise automatic postural reactions. Such an exclusive focus on these highly stereotypical reactions would fail to adequately address how we can modify these reactions should the need arise (e.g., avoiding an obstacle with a recovery step). This would appear to be a glaring omission when one considers the enormous complexity of the environments we face daily. Overall, the status quo when evaluating the neural control of balance fails to truly expose how higher brain resources contribute to preventing falls in complex settings. The present protocol offers a way to require suppression of automatic, but inappropriate corrective balance reactions, and force a selection among alternative action choices to successfully recover balance following postural perturbation.

Here we offer a protocol that allows the user to selectively change affordances and/or constraints on movements that are relevant for recovering balance after postural perturbation.

Assessment of reactive balance traditionally imposes some type of perturbation to upright stance or gait followed by measurement of the resultant ...

Capturing Dynamic Finger Gesturing with High-resolution Surface Electromyography and Computer Vision

Finger gestures are a critical element in human communication, and as such, finger gesture recognition is widely studied as a human-computer interface for state-of-the-art prosthetics and optimized rehabilitation. Surface electromyography (sEMG), in conjunction with deep learning methods, is considered a promising method in this domain. However, current methods often rely on cumbersome recording setups and the identification of static hand positions, limiting their effectiveness in real-world applications. The protocol we report here presents an advanced approach combining a wearable surface EMG and finger&#160;tracking system to capture comprehensive data during dynamic hand movements. The method records muscle activity from soft printed electrode arrays (16 electrodes) placed on the forearm as subjects perform gestures in different hand positions and during movement. Visual instructions prompt subjects to perform specific gestures while EMG and finger positions are recorded. The integration of synchronized EMG recordings and finger tracking data enables comprehensive analysis of muscle activity patterns and corresponding gestures. The reported approach demonstrates the potential of combining EMG and visual tracking technologies as an important resource for developing intuitive and responsive gesture recognition systems with applications in prosthetics, rehabilitation, and interactive technologies. This protocol aims to guide researchers and practitioners, fostering further innovation and application of gesture recognition in dynamic and real-world scenarios.

The paper presents a comprehensive protocol for simultaneously recording hand-electromyography (EMG) and visual finger tracking during natural finger gesturing. The visual data is designed to serve as the ground truth for the development of accurate EMG-based computational models for finger gesture recognition.

Finger gestures are a critical element in human communication, and as such, finger gesture recognition is widely studied as a human-computer interface for ...

Bioengineering

Assessing Corticospinal Excitability During Goal-Directed Reaching Behavior

Reaching is a widely studied behavior in motor physiology and neuroscience research. While reaching has been examined using a variety of behavioral manipulations, there remain significant gaps in the understanding of the neural processes involved in reach planning, execution, and control. The novel approach described here combines a two-dimensional reaching task with transcranial magnetic stimulation (TMS) and concurrent electromyography (EMG) recording from multiple muscles. This method allows for the noninvasive detection of corticospinal activity at precise time points during the unfolding of reaching movements. The example task code includes a delayed response reaching task with two possible targets displayed &#177; 45&#176; off the midline. Single pulse TMS is delivered on the majority of task trials, either at the onset of the preparatory cue (baseline) or 100 ms prior to the imperative cue (delay). This sample design is suitable for investigating changes in corticospinal excitability during reach preparation. The sample code also includes a visuomotor perturbation (i.e., cursor rotation of &#177; 20&#176;) to investigate the effects of adaptation on corticospinal excitability during reach preparation. The task parameters and TMS delivery can be adjusted to address specific hypotheses about the state of the motor system during reaching behavior. In the initial implementation, motor evoked potentials (MEPs) were successfully elicited on 83% of TMS trials, and reach trajectories were recorded on all trials.

Reaching is a fundamental skill that allows humans to interact with the environment. Several studies have aimed to characterize reaching behavior using a variety of methodologies. This paper offers an open-source application of transcranial magnetic stimulation to assess the state of corticospinal excitability in humans during reaching task performance.

Reaching is a widely studied behavior in motor physiology and neuroscience research. While reaching has been examined using a variety of behavioral ...

An Emerging Target Paradigm to Evoke Fast Visuomotor Responses on Human Upper Limb Muscles

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