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.</td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td>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

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4.2K Views.  Western University. Presented here is a behavioral paradigm that elicits robust fast visuomotor responses on human upper limb muscles during visually guided reaches.

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

Recording Behavioral Responses to Reflection in Crayfish

Social behavior depends on sensory input from the visual, mechanical and olfactory systems. One important issue concerns the relative roles of each sensory modality in guiding behavior. The role of visual inputs has been examined by isolating visual stimuli from mechanical and chemosensory stimuli. In some studies (Bruski &amp; Dunham, 1987: Delgado-Morales et al., 2004) visual inputs have been removed with blindfolds or low light intensity, and effects of remaining sensory modalities have been elucidated. An alternative approach is to study the effects of visual inputs in the absence of any appropriate mechanical and chemosensory cues. This approach aims to identify the exclusive role of visual inputs. 
We have used two methods to provide visual stimuli to crayfish without providing chemical and mechanical cues. In one method, crayfish are videotaped in an aquarium where half of the walls are covered in mirrors to provide a reflective environment, and the other half are covered in a non-reflective (matte finish) plastic. This gives the crayfish a choice between reflective and non-reflective environments. The reflective environment provides visual cues in the form of reflected images of the crayfish as it moves throughout half of the tank; these visual cues are missing from the non-reflective half of the tank. An alternative method is to videotape the behavior of crayfish in an aquarium separated by a smaller chamber at each end, with a crayfish in one small chamber providing visual cues and an inert object in the opposite small chamber providing visual input from a non-moving, non-crayfish source. 
Our published results indicate that responses of crayfish to the reflective environment depend on socialization and dominance rank. Socialized crayfish spent more time in the reflective environment and exhibited certain behaviors more frequently there than in the non-reflective environment; isolated crayfish showed no such differences. Crayfish that were housed in same-sex pairs developed a social rank of either dominant or subordinate. Responses to reflection differed between dominant and subordinate crayfish (May &amp; Mercier, 2006; May &amp; Mercier, 2007). Dominant crayfish spent more time on the reflective side, entered reflective corners more frequently and spent more time in reflective corners compared to the non-reflective side. Subordinate crayfish walked in reverse more often on the reflective side than on the non-reflective side. Preliminary data suggest similar effects from visual cues provided by a crayfish in a small adjoining chamber (May et al., 2008).

We have developed two methods for studying effects of visual cues on behavior in the absence of tactile and chemical cues. One method involves videotaping responses of crayfish to reflective walls in an aquarium; the other examines effects of visual inputs provided by a live crayfish behind a transparent partition.

Social behavior depends on sensory input from the visual, mechanical and olfactory systems.  One important issue concerns the relative roles of each ...

Vibrodissociation of Neurons from Rodent Brain Slices to Study Synaptic Transmission and Image Presynaptic Terminals

Mechanical dissociation of neurons from the central nervous system has the advantage that presynaptic boutons remain attached to the isolated neuron of interest. This allows for examination of synaptic transmission under conditions where the extracellular and postsynaptic intracellular environments can be well controlled. A vibration-based technique without the use of proteases, known as vibrodissociation, is the most popular technique for mechanical isolation. A micropipette, with the tip fire-polished to the shape of a small ball, is placed into a brain slice made from a P1-P21 rodent. The micropipette is vibrated parallel to the slice surface and lowered through the slice thickness resulting in the liberation of isolated neurons. The isolated neurons are ready for study within a few minutes of vibrodissociation. This technique has advantages over the use of primary neuronal cultures, brain slices and enzymatically isolated neurons including: rapid production of viable, relatively mature neurons suitable for electrophysiological and imaging studies; superior control of the extracellular environment free from the influence of neighboring cells; suitability for well-controlled pharmacological experiments using rapid drug application and total cell superfusion; and improved space-clamp in whole-cell recordings relative to neurons in slice or cell culture preparations. This preparation can be used to examine synaptic physiology, pharmacology, modulation and plasticity. Real-time imaging of both pre- and postsynaptic elements in the living cells and boutons is also possible using vibrodissociated neurons. Characterization of the molecular constituents of pre- and postsynaptic elements can also be achieved with immunological and imaging-based approaches.

This report demonstrates a technique for mechanical isolation of individual viable neurons retaining attached presynaptic boutons. Vibrodissociated neurons have the advantages of rapid production, excellent pharmacological control and improved space-clamp without influence from neighboring cells. This method can be used for imaging of synaptic elements and patch-clamp recording.

Mechanical dissociation of neurons from the central nervous system has the advantage that presynaptic boutons remain attached to the isolated neuron of ...

Correlating Behavioral Responses to fMRI Signals from Human Prefrontal Cortex: Examining Cognitive Processes Using Task Analysis

The aim of this methods paper is to describe how to implement a neuroimaging technique to examine complementary brain processes engaged by two similar tasks. Participants' behavior during task performance in an fMRI scanner can then be correlated to the brain activity using the blood-oxygen-level-dependent signal. We measure behavior to be able to sort correct trials, where the subject performed the task correctly and then be able to examine the brain signals related to correct performance. Conversely, if subjects do not perform the task correctly, and these trials are included in the same analysis with the correct trials we would introduce trials that were not only for correct performance. Thus, in many cases these errors can be used themselves to then correlate brain activity to them. We describe two complementary tasks that are used in our lab to examine the brain during suppression of an automatic responses: the stroop1 and anti-saccade tasks. The emotional stroop paradigm instructs participants to either report the superimposed emotional 'word' across the affective faces or the facial 'expressions' of the face stimuli1,2. When the word and the facial expression refer to different emotions, a conflict between what must be said and what is automatically read occurs. The participant has to resolve the conflict between two simultaneously competing processes of word reading and facial expression. Our urge to read out a word leads to strong 'stimulus-response (SR)' associations; hence inhibiting these strong SR's is difficult and participants are prone to making errors. Overcoming this conflict and directing attention away from the face or the word requires the subject to inhibit bottom up processes which typically directs attention to the more salient stimulus. Similarly, in the anti-saccade task3,4,5,6, where an instruction cue is used to direct only attention to a peripheral stimulus location but then the eye movement is made to the mirror opposite position. Yet again we measure behavior by recording the eye movements of participants which allows for the sorting of the behavioral responses into correct and error trials7 which then can be correlated to brain activity. Neuroimaging now allows researchers to measure different behaviors of correct and error trials that are indicative of different cognitive processes and pinpoint the different neural networks involved.

The goal of our research is to correlate behavior to brain activity. Accurate behavioral measures and imaging techniques allow us to elucidate brain-behavior relationships.

The aim of this methods paper is to describe how to implement a neuroimaging technique to examine complementary brain processes engaged by two similar ...

An Injury Paradigm to Investigate Central Nervous System Repair in Drosophila

An experimental method has been developed to investigate the cellular responses to central nervous system (CNS) injury using the fruit-fly Drosophila. Understanding repair and regeneration in animals is a key question in biology. The damaged human CNS does not regenerate, and understanding how to promote the regeneration is one of main goals of medical neuroscience. The powerful genetic toolkit of Drosophila can be used to tackle the problem of CNS regeneration.
A lesion to the CNS ventral nerve cord (VNC, equivalent to the vertebrate spinal cord) is applied manually with a tungsten needle. The VNC can subsequently be filmed in time-lapse using laser scanning confocal microscopy for up to 24 hr to follow the development of the lesion over time. Alternatively, it can be cultured, then fixed and stained using immunofluorescence to visualize neuron and glial cells with confocal microscopy. Using appropriate markers, changes in cell morphology and cell state as a result of injury can be visualized. With ImageJ and purposely developed plug-ins, quantitative and statistical analyses can be carried out to measure changes in wound size over time and the effects of injury in cell proliferation and cell death. These methods allow the analysis of large sample sizes. They can be combined with the powerful genetics of Drosophila to investigate the molecular mechanisms underlying CNS regeneration and repair.

An Injury Paradigm to Investigate Central Nervous System Repair in Drosophila

An injury paradigm using the Drosophila larval ventral nerve cord to investigate central nervous system regeneration and repair is described. Stabbing followed by laser scanning confocal microscopy in time-lapse and fixed specimens, combined with quantitative analysis with purposefully developed software and genetics, are used to investigate the molecular mechanisms of CNS regeneration and repair.

An experimental method has been developed to investigate the cellular responses to central nervous system (CNS) injury using the fruit-fly Drosophila. ...

Electrophysiological Method for Recording Intracellular Voltage Responses of Drosophila Photoreceptors and Interneurons to Light Stimuli In Vivo

Voltage responses of insect photoreceptors and visual interneurons can be accurately recorded with conventional sharp microelectrodes. The method described here enables the investigator to measure long-lasting (from minutes to hours) high-quality intracellular responses from single Drosophila R1-R6 photoreceptors and Large Monopolar Cells (LMCs) to light stimuli. Because the recording system has low noise, it can be used to study variability among individual cells in the fly eye, and how their outputs reflect the physical properties of the visual environment. We outline all key steps in performing this technique. The basic steps in constructing an appropriate electrophysiology set-up for recording, such as design and selection of the experimental equipment are described. We also explain how to prepare for recording by making appropriate (sharp) recording and (blunt) reference electrodes. Details are given on how to fix an intact fly in a bespoke fly-holder, prepare a small window in its eye and insert a recording electrode through this hole with minimal damage. We explain how to localize the center of a cell's receptive field, dark- or light-adapt the studied cell, and to record its voltage responses to dynamic light stimuli. Finally, we describe the criteria for stable normal recordings, show characteristic high-quality voltage responses of individual cells to different light stimuli, and briefly define how to quantify their signaling performance. Many aspects of the method are technically challenging and require practice and patience to master. But once learned and optimized for the investigator's experimental objectives, it grants outstanding in vivo neurophysiological data.

Electrophysiological Method for Recording Intracellular Voltage Responses of Drosophila Photoreceptors and Interneurons to Light Stimuli In Vivo

Sharp microelectrodes enable accurate electrophysiological characterization of photoreceptor and visual interneuron output in living Drosophila. Here we show how to use this method to record high-quality voltage responses of individual cells to controlled light stimulation. This method is ideal for studying neural information processing in insect compound eyes.

Voltage responses of insect photoreceptors and visual interneurons can be accurately recorded with conventional sharp microelectrodes. The method ...

A Computerized Test Battery to Study Pharmacodynamic Effects on the Central Nervous System of Cholinergic Drugs in Early Phase Drug Development

Investigating potential pharmacodynamic effects in an early phase of central nervous system (CNS) drug research can provide valuable information for further development of new compounds. A computerized and thoroughly validated battery of neuropsychological and neurophysiological tests has been shown to be sensitive to detect drug-induced effects of multiple new and existing compounds. The test battery covers the main CNS domains, which have been shown to respond to drug effects and can be repeatedly administered following drug administration to characterize the concentration-effect profile of a drug.
The standard tests in the battery are saccadic eye movement, smooth pursuit eye movement, the Bowdle visual analog scale (VAS), the Bond and Lader VAS, body sway, adaptive tracking, visual verbal learning, and quantitative electroencephalography (qEEG). However, the test battery is adaptive in nature, meaning that it can be composed and adjusted with tests fit to investigate specific drug classes, or even specific receptors.
Showing effects of new cholinergic drugs designed to have a pro-cognitive outcome has been difficult. The pharmacological challenge model is a tool for early proof-of-pharmacology. Here, a marketed drug is used to induce temporary and reversible disease-like symptoms in healthy subjects, via a pharmacological mechanism related to the disease that is targeted as indication for the new compound. The test battery was implemented to investigate the potential of the nicotinic receptor antagonist mecamylamine to be used as a challenge model for cholinergic dysfunction, as seen in neurodegenerative disorders.
A worsening of scores in a dose dependent manner on the visual verbal learning test (VVLT; a test for learning and memory abilities) and the adaptive tracking test (a measure of visuomotor control and arousal), in particular, showed that the test battery is sensitive to showing acute pharmacodynamic effect after administration of anti-cholinergic drugs.

A validated computerized battery of neuropsychological and neurophysiological tests is used to study pharmacodynamic effects on the central nervous system of newly developed drugs in early phase development. To demonstrate the test battery, the acute effects of mecamylamine and the reversal of these effects by two agonist drugs are described.

Investigating potential pharmacodynamic effects in an early phase of central nervous system (CNS) drug research can provide valuable information for ...

An In Ovo Model for Testing Insulin-mimetic Compounds

Elevated blood glucose levels in type 2 diabetes mellitus (T2DM), a complex and multifactorial metabolic disease, are caused by insulin resistance and &#946;-cell failure. Various strategies, including the injection of insulin or the usage of insulin-sensitizing drugs, were pursued to treat T2DM or at least reduce the symptoms. In addition, the application of herbal compounds has attracted increasing attention. Thus, it is necessary to find efficient test systems to identify and characterize insulin-mimetic compounds. Here we developed a modified chick embryo model, which enables testing of synthetic compounds and herbal extracts with insulin-mimetic properties. Using a fluorescence microscopy-based primary screen, which quantifies the translocation of Glucose transporter 4 (Glut4) to the plasma membrane, we were able to identify compounds, mainly herbal extracts, which lead to an increase of intracellular glucose concentrations in adipocytes. However, the efficacy of these substances requires further verification in a living organism. Thus, we used an in-ovo approach to identify their blood glucose-reducing properties. The approval by an ethics committee is not needed since the use of chicken embryos during the first two-thirds of embryonic development is not considered an animal experiment. Here, the application of this model is described in detail.

An In Ovo Model for Testing Insulin-mimetic Compounds

In this study, we describe an in-ovo system as a promising tool to test insulin-mimetic compounds in a living organism. The main advantages include adequate throughput rates and acceptable costs, which enable the identification of phytochemicals with insulin-mimetic properties.

Elevated blood glucose levels in type 2 diabetes mellitus (T2DM), a complex and multifactorial metabolic disease, are caused by insulin resistance and ...

FM Dye Cycling at the Synapse: Comparing High Potassium Depolarization, Electrical and Channelrhodopsin Stimulation

FM dyes are used to study the synaptic vesicle (SV) cycle. These amphipathic probes have a hydrophilic head and hydrophobic tail, making them water-soluble with the ability to reversibly enter and exit membrane lipid bilayers. These styryl dyes are relatively non-fluorescent in aqueous medium, but insertion into the outer leaflet of the plasma membrane causes a &#62;40X increase in fluorescence. In neuronal synapses, FM dyes are internalized during SV endocytosis, trafficked both within and between SV pools, and released with SV exocytosis, providing a powerful tool to visualize presynaptic stages of neurotransmission. A primary genetic model of glutamatergic synapse development and function is the Drosophila neuromuscular junction (NMJ), where FM dye imaging has been used extensively to quantify SV dynamics in a wide range of mutant conditions. The NMJ synaptic terminal is easily accessible, with a beautiful array of large synaptic boutons ideal for imaging applications. Here, we compare and contrast the three ways to stimulate the Drosophila NMJ to drive activity-dependent FM1-43 dye uptake/release: 1) bath application of high [K+] to depolarize neuromuscular tissues, 2) suction electrode motor nerve stimulation to depolarize the presynaptic nerve terminal, and 3) targeted transgenic expression of channelrhodopsin variants for light-stimulated, spatial control of depolarization. Each of these methods has benefits and disadvantages for the study of genetic mutation effects on the SV cycle at the Drosophila NMJ. We will discuss these advantages and disadvantages to assist the selection of the stimulation approach, together with the methodologies specific to each strategy. In addition to fluorescent imaging, FM dyes can be photoconverted to electron-dense signals visualized using transmission electron microscopy (TEM) to study SV cycle mechanisms at an ultrastructural level. We provide the comparisons of confocal and electron microscopy imaging from the different methods of Drosophila NMJ stimulation, to help guide the selection of future experimental paradigms.

Synaptic vesicle (SV) cycling is the core mechanism of intercellular communication at neuronal synapses. FM dye uptake and release are the primary means of quantitatively assaying SV endo- and exocytosis. Here, we compare all the stimulation methods to drive FM1-43 cycling at the Drosophila neuromuscular junction (NMJ) model synapse.

FM dyes are used to study the synaptic vesicle (SV) cycle. These amphipathic probes have a hydrophilic head and hydrophobic tail, making them ...

The Combined Use of Transcranial Direct Current Stimulation and Robotic Therapy for the Upper Limb

Neurologic disorders such as stroke and cerebral palsy are leading causes of long-term disability and can lead to severe incapacity and restriction of daily activities due to lower and upper limb impairments. Intensive physical and occupational therapy are still considered main treatments, but new adjunct therapies to standard rehabilitation that may optimize functional outcomes are being studied.
Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that polarizes underlying brain regions through the application of weak direct currents through electrodes on the scalp, modulating cortical excitability. Increased interest in this technique can be attributed to its low cost, ease of use, and effects on human neural plasticity. Recent research has been performed to determine the clinical potential of tDCS in diverse conditions such as depression, Parkinson&#39;s disease, and motor rehabilitation after stroke. tDCS helps enhance brain plasticity and seems to be a promising technique in rehabilitation programs.
A number of robotic devices have been developed to assist in the rehabilitation of upper limb function after stroke. The rehabilitation of motor deficits is often a long process requiring multidisciplinary approaches for a patient to achieve maximum independence. These devices do not intend to replace manual rehabilitation therapy; instead, they were designed as an additional tool to rehabilitation programs, allowing immediate perception of results and tracking of improvements, thus helping patients to stay motivated.
Both tDSC and robot-assisted therapy are promising add-ons to stroke rehabilitation and target the modulation of brain plasticity, with several reports describing their use to be associated with conventional therapy and the improvement of therapeutic outcomes. However, more recently, some small clinical trials have been developed that describe the associated use of tDCS and robot-assisted therapy in stroke rehabilitation. In this article, we describe the combined methods used in our institute for improving motor performance after stroke.

The combined use of transcranial direct current stimulation and robotic therapy as an add-on for conventional rehabilitation therapy may result in improved therapeutic outcomes due to modulation of brain plasticity. In this article, we describe the combined methods used in our institute for improving motor performance after stroke.

Neurologic disorders such as stroke and cerebral palsy are leading causes of long-term disability and can lead to severe incapacity and restriction of ...

The Evoked Potential Operant Conditioning System (EPOCS): A Research Tool and an Emerging Therapy for Chronic Neuromuscular Disorders

The Evoked Potential Operant Conditioning System (EPOCS) is a software tool that implements protocols for operantly conditioning stimulus-triggered muscle responses in people with neuromuscular disorders, which in turn can improve sensorimotor function when applied appropriately. EPOCS monitors the state of specific target muscles&#8212;e.g., from surface electromyography (EMG) while standing, or from gait cycle measurements while walking on a treadmill&#8212;and automatically triggers calibrated stimulation when pre-defined conditions are met. It provides two forms of feedback that enable a person to learn to modulate the targeted pathway&#39;s excitability. First, it continuously monitors ongoing EMG activity in the target muscle, guiding the person to produce a consistent level of activity suitable for conditioning. Second, it provides immediate feedback of the response size following each stimulation and indicates whether it has reached the target value.
To illustrate its use, this article describes a protocol through which a person can learn to decrease the size of the Hoffmann reflex&#8212;the electrically-elicited analog of the spinal stretch reflex&#8212;in the soleus muscle. Down-conditioning this pathway&#39;s excitability can improve walking in people with spastic gait due to incomplete spinal cord injury. The article demonstrates how to set up the equipment; how to place stimulating and recording electrodes; and how to use the free software to optimize electrode placement, measure the recruitment curve of direct motor and reflex responses, measure the response without operant conditioning, condition the reflex, and analyze the resulting data. It illustrates how the reflex changes over multiple sessions and how walking improves. It also discusses how the system can be applied to other kinds of evoked responses and to other kinds of stimulation, e.g., motor evoked potentials to transcranial magnetic stimulation; how it can address various clinical problems; and how it can support research studies of sensorimotor function in health and disease.

The Evoked Potential Operant Conditioning System EPOCS: A Research Tool and an Emerging Therapy for Chronic Neuromuscular Disorders

The Evoked Potential Operant Conditioning System aids scientific investigation of sensorimotor function and can administer targeted neurobehavioral training that can impact sensorimotor rehabilitation in neuromuscular disorders. This article describes its capabilities and illustrates its application in modifying a simple spinal reflex to achieve lasting improvement in motor function.

The Evoked Potential Operant Conditioning System (EPOCS) is a software tool that implements protocols for operantly conditioning stimulus-triggered muscle ...

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

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Recording Behavioral Responses to Reflection in Crayfish

Vibrodissociation of Neurons from Rodent Brain Slices to Study Synaptic Transmission and Image Presynaptic Terminals

Correlating Behavioral Responses to fMRI Signals from Human Prefrontal Cortex: Examining Cognitive Processes Using Task Analysis

An Injury Paradigm to Investigate Central Nervous System Repair in Drosophila

Electrophysiological Method for Recording Intracellular Voltage Responses of Drosophila Photoreceptors and Interneurons to Light Stimuli In Vivo

A Computerized Test Battery to Study Pharmacodynamic Effects on the Central Nervous System of Cholinergic Drugs in Early Phase Drug Development

An In Ovo Model for Testing Insulin-mimetic Compounds

FM Dye Cycling at the Synapse: Comparing High Potassium Depolarization, Electrical and Channelrhodopsin Stimulation

The Combined Use of Transcranial Direct Current Stimulation and Robotic Therapy for the Upper Limb

The Evoked Potential Operant Conditioning System (EPOCS): A Research Tool and an Emerging Therapy for Chronic Neuromuscular Disorders