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The literature on speed-accuracy trade-off (SAT) in motor control has evidenced individuality in how individuals trade moments (e.g.. mean and variance) of spatial and temporal errors. These individual tendencies could grasp tendencies of the system given previous experiences and constraints of the organism, a signature of the system control. Nonetheless, such tendency must be robust to small perturbations. Thirty participants performed nine conditions with different time and spatial criteria over 2 days (scanning). In between these scanning conditions, individuals performed a practice condition that required modifications of the individuals' preferred spatial and temporal tendency in the SAT. Our results demonstrated that there were no systematic effects of practice in SAT preferences. However, individual analyses demonstrated significant changes for 25 out of 30 individuals. The latter either attests against a consistent preference or to a more complex characterization of individual SAT tendencies. [ABSTRACT FROM AUTHOR]

Background: The core stability program is commonly utilized as an intervention method to improve postural control. This study aimed to evaluate the effect of core stability exercises on upper limb reaching in children with hemiparetic cerebral palsy (CP). For this purpose, 30 hemiparetic CP children of both sexes were recruited for the study. The children were between the ages of 4 and 6. According to the modified Ashworth scale (MAS), the degree of spasticity varied from 1 to 1 + , and for children who were selected, the average Trunk Control Measurement Scale (TCMS) ranged from 25 to 42. Children were assigned into two groups at random (study group and control group). The pediatric reach test (PRT) was used to assess each child both before and after two consecutive months of therapy. The children in both groups received the same program of selected physical therapy exercises, but the children in the study group also performed the selected physical therapy program in addition to the core stability exercises. Results: By comparing the mean values of all assessed variables before and after therapy, both groups improved significantly (p = 0.0001). When comparing post-treatment outcomes, there were significant differences between the control and study groups in all assessed variables (p = 0.0001) in favor of the study group. Conclusion: Core stability exercises may be used to improve reaching in children with hemiparetic cerebral palsy. Trial registration: This study was authorized by the Faculty of Physical Therapy's ethics committee under the number "REC/012/003125" and registered in ClinicalTrial.gov with the number "NCT05316090" on 9 April 2022 retrospectively. [ABSTRACT FROM AUTHOR]

Patients with Mild Cognitive Impairment (MCI) may exhibit poorer performance in visuomotor tasks than healthy individuals, particularly under conditions with high cognitive load. Few studies have examined reaching movements in MCI and did so without assessing susceptibility to distractor interference. This proof-of-concept study analyzed the kinematics of visually guided reaching movements towards a target dot placed along the participants' midsagittal/reaching axis. Movements were performed with and without a visual distractor (flanker) at various distances from the reaching axis. Participants were instructed to avoid "touching" the flanker during movement execution. The whole sample included 11 patients with MCI due to Alzheimer's disease, 10 healthy older adults, and 12 healthy young adults, all right-handed. Patients with MCI performed reaching movements whose trajectories deviated significantly away from the flanker, especially when it was 1 mm away, with less consistent trajectories than controls. Also, our results suggest that trajectory curvature may discriminate between patients with MCI and healthy older adults. The analysis of reaching movements under conditions of visual interference may enhance the diagnosis of MCI, underscoring the need for multidimensional assessments incorporating both cognitive and motor domains. [ABSTRACT FROM AUTHOR]

Many motor tasks are comprised of sequentially linked action phases, as when reaching for, lifting, transporting, and replacing a cup of coffee. During such tasks, discrete visual, auditory and/or haptic feedback are typically associated with mechanical events at the completion of each action phase, as when breaking and subsequently making contact between the cup and the table. An emerging concept is that important sensorimotor control operations, that affect subsequent action phases, are centred on these discrete multisensory events. By predicting sensory feedback at the completion of action phases, and comparing with the actual feedback that arises, task performance can be continuously monitored. If errors are detected, the sensorimotor system can quickly respond with task-protective corrective actions. The aim of this study was to investigate how discrete multisensory feedback at the completion of action phases are used in these control operations. To investigate this question, 42 healthy human participants (both male and female) performed a visually guided sequential reaching task where auxiliary discrete visual, auditory and/or haptic feedback was associated with the completion of action phases. Occasionally however, this feedback was removed in one or two modalities. The results show that although the task was visually guided, its control was critically influenced by discrete auditory and haptic feedback. Multisensory integration effects occurred, that enhanced the corrective actions, when auditory feedback was unexpectedly removed along with haptic or visual feedback. This multisensory enhancement may facilitate the ability to detect errors during sequential actions and amplify task-protective corrective actions. [ABSTRACT FROM AUTHOR]

The interplay between attention, alertness, and motor planning is crucial for our manual interactions. To investigate the neural bases of this interaction and challenge the views that attention cannot be disentangled from motor planning, we instructed human volunteers of both sexes to plan and execute reaching movements while attending to the target, while attending elsewhere, or without constraining attention. We recorded reaction times to reach initiation and pupil diameter and interfered with the functions of the medial posterior parietal cortex (mPPC) with online repetitive transcranial magnetic stimulation to test the causal role of this cortical region in the interplay between spatial attention and reaching. We found that mPPC plays a key role in the spatial association of reach planning and covert attention. Moreover, we have found that alertness, measured by pupil size, is a good predictor of the promptness of reach initiation only if we plan a reach to attended targets, and mPPC is causally involved in this coupling. Different from previous understanding, we suggest that mPPC is neither involved in reach planning per se, nor in sustained covert attention in the absence of a reach plan, but it is specifically involved in attention functional to reaching. [ABSTRACT FROM AUTHOR]

Abstract Background The core stability program is commonly utilized as an intervention method to improve postural control. This study aimed to evaluate the effect of core stability exercises on upper limb reaching in children with hemiparetic cerebral palsy (CP). For this purpose, 30 hemiparetic CP children of both sexes were recruited for the study. The children were between the ages of 4 and 6. According to the modified Ashworth scale (MAS), the degree of spasticity varied from 1 to 1 + , and for children who were selected, the average Trunk Control Measurement Scale (TCMS) ranged from 25 to 42. Children were assigned into two groups at random (study group and control group). The pediatric reach test (PRT) was used to assess each child both before and after two consecutive months of therapy. The children in both groups received the same program of selected physical therapy exercises, but the children in the study group also performed the selected physical therapy program in addition to the core stability exercises. Results By comparing the mean values of all assessed variables before and after therapy, both groups improved significantly (p = 0.0001). When comparing post-treatment outcomes, there were significant differences between the control and study groups in all assessed variables (p = 0.0001) in favor of the study group. Conclusion Core stability exercises may be used to improve reaching in children with hemiparetic cerebral palsy. Trial registration This study was authorized by the Faculty of Physical Therapy’s ethics committee under the number “REC/012/003125” and registered in ClinicalTrial.gov with the number “NCT05316090” on 9 April 2022 retrospectively.

Background: The prefrontal cortex (PFC) is an important node for action planning in the frontoparietal reaching network but its role in reaching in children with cerebral palsy (CP) is unexplored. This case–control study combines a robotic task with functional near-infrared spectroscopy (fNIRS) to concurrently assess reaching accuracy and PFC activity during time-constrained, goal-directed reaching in children with CP. We hypothesized that reaching accuracy in children with CP would be lower than in typically developing children and would be related to PFC activity. Methods: Fourteen children with spastic CP (5-11 y; Manual Ability Classification System level I-II) and 14 age-, sex- and arm dominance-matched typically developing controls performed seated uniplanar reaches with a robotic arm (KINARM End-Point Lab) to hit visual targets projected onto a screen. Four blocks of 10 reaching trials each were performed for each arm. Time constraint (high, low) was varied across blocks by changing the time participants had to hit the target. Results: Children with CP displayed lower reaching accuracy compared to controls, with greater deficits observed in the non-preferred arm (d = 1.916, p < 0.001) than the preferred arm (d = 1.033, p = 0.011). Inter-limb differences in accuracy were observed only in children with CP (d = 0.839, p < 0.001). PFC activity differed across groups during preferred arm reaching, with PFC deactivation observed in children with CP under high time constraints compared to PFC activation in controls (d = 1.086, p = 0.006). Children with CP also exhibited lower PFC activity under high time constraint compared to low time constraint in the preferred arm (d = 0.702, p = 0.001). PFC activity was positively related to reaching accuracy across time constraints in both arms in children with CP, but not in controls. Conclusions: Contrasting patterns of PFC activity observed in children with CP compared to age- and sex-matched controls during a robotic reaching task lends support for the concurrent use of fNIRS and robotics to assess goal-directed reaching in CP. Trial Registration: Data collected as part of a larger randomized controlled trial; https://clinicaltrials.gov/ct2/show/NCT03484078 [ABSTRACT FROM AUTHOR]

Purpose/aim: The ability to perform routine tasks during reaching and activities of daily living (ADLs) is impaired as a result of deterioration in the postural adjustments after stroke. Trunk stability is needed to maintain balance, correct scapular position and posture while moving the upper extremity. The objective was to examine the effect of scapular exercises on the scapular stability, trunk control and ADLs. Materials and methods: Patients (50–85 years) with acute hemiparetic stroke were participated in this double blind randomized controlled study. The patients in both group were treated with the exercise program according to the Bobath concept and isometric scapular exercises were applied to the study group in addition to these exercises. The participants in both groups were taken into the physiotherapy program for 5 days and each program were taken 30 min. Patient assessment included Lateral scapular slide test (LSST), Trunk Impairment Scale (TIS), Trunk Control Test (TCT), Modified Barthel Index (MBI) and Reaching Performance Test (RPT). Results: Significant increases were observed distance in protraction, between protraction – retraction at 90° of shoulder abduction and flexion and retraction in 90° of shoulder abduction within both groups. Only the study group produced improvement in protraction of 90° of shoulder flexion (p < 0.05). While both groups achieved a significant improvement in TIS, MBI, RPT scores, TCT scores increased significantly only in study group (p < 0.05). Conclusions: The adding isometric scapular exercises to the rehabilitation program significantly increased the effectivity of neurorehabilitation on increasing trunk control, independence during ADLs, reaching performance and reducing trunk impairment. [ABSTRACT FROM AUTHOR]

A vexing characteristic of motor disability after stroke is that many individuals fail to use their affected arm effectively despite having the capacity to do so, a phenomenon termed arm nonuse. Based on the hypothesis that nonuse is influenced by the competing cognitive demands of many daily activities, we examined the effects of cognitive load on arm choice and motor performance in individuals with stroke using a novel virtual reality paradigm that mimics the demands of real-life visual search, object selection, and reaching to targets. Twenty individuals with single left or right hemispheric chronic stroke (11 left cerebrovascular accident; 9 right cerebrovascular accident) and 10 age-matched neurotypical participants completed the Virtual Reality Arm Choice task, in which they reached for target objects in an array under varied cognitive demand. To manipulate cognitive demand, we varied the semantic similarity of objects in the reaching space and the presence or absence of a secondary task. The results showed reduced use of the paretic arm under increased demand. Under cognitive load, participants with stroke also showed slower reach initiation, slower movements, increased reach curvature, and increased performance differences between the paretic and non-paretic arms. The arm choice of neurotypical individuals was also modulated under cognitive load. These data indicate that cognitive factors influence arm choice and motor performance in naturalistic reaching tasks in individuals with chronic stroke. Performance decrements under cognitive load may in turn influence reduced paretic arm use during daily activities. [ABSTRACT FROM AUTHOR]

Interlimb differences in reach control could impact the learning of a motor sequence that requires whole-arm movements. The purpose of this study was to investigate the learning of an implicit, 3-dimensional whole-arm sequence task with the non-dominant left arm compared to the dominant right arm. Thirty-one right-hand dominant adults completed two consecutive days of practice of a motor sequence task presented in a virtual environment with either their dominant right or non-dominant left arm. Targets were presented one-at-a-time alternating between Random and Repeated sequences. Task performance was indicated by the time to complete the sequence (response time), and kinematic measures (hand path distance, peak velocity) were used to examine how movements changed over time. While the Left Arm group was slower than the Right Arm group at baseline, both groups significantly improved response time with practice with the Left Arm group demonstrating greater gains. The Left Arm group improved performance by decreasing hand path distance (straighter path to targets) while the Right Arm group improved performance through a smaller decrease in hand path distance combined with increasing peak velocity. Gains made during practice on Day 1 were retained on Day 2 for both groups. Overall, individuals reaching with the non-dominant left arm learned the whole-arm motor sequence task but did so through a different strategy than individuals reaching with the dominant right arm. The strategy adopted for the learning of movement sequences that require whole-arm movements may be impacted by differences in reach control between the nondominant and dominant arms. [ABSTRACT FROM AUTHOR]

Background: Many daily activities depend on visual inputs to improve motor accuracy and minimize errors. Reaching tasks present an ecological framework for examining these visuomotor interactions, but our comprehension of how different amounts of visual input affect motor outputs is still limited. The present study fills this gap, exploring how hand-related visual bias affects motor performance in a reaching task (to draw a line between two dots). Methods: Our setup allowed us to show and hide the visual feedback related to the hand position (cursor of a computer mouse), which was further disentangled from the visual input related to the task (tip of the line). Results: Data from 53 neurotypical participants indicated that, when the hand-related visual cue was visible and disentangled from the task-related visual cue, accommodating movements in response to spatial distortions were less accurate than when the visual cue was absent. Conclusions: We interpret these findings with reference to the concepts of motor affordance of visual cues, shifts between internally- and externally-oriented cognitive strategies to perform movements, and body-related reference frames. [ABSTRACT FROM AUTHOR]

Attention is needed to perform goal-directed vision-guided movements. We investigated whether the direction of covert attention modulates movement outcomes and dynamics. Right-handed and left-handed volunteers attended to a spatial location while planning a reach toward the same hemifield, the opposite one, or planned a reach without constraining attention. We measured behavioral variables as outcomes of ipsilateral and contralateral reaching and the tangling of behavioral trajectories obtained through principal component analysis as a measure of the dynamics of motor control. We found that the direction of covert attention had significant effects on the dynamics of motor control, specifically during contralateral reaching. Data suggest that motor control was more feedback-driven when attention was directed leftward than when attention was directed rightward or when it was not constrained, irrespectively of handedness. These results may help to better understand the neural bases of asymmetrical neurological diseases like hemispatial neglect. [ABSTRACT FROM AUTHOR]

Although the stereoscopic effect in 3D virtual reality (VR) space has been studied, its influence on motor performance, specifically how stereoscopic objects affect behavioral outcomes like reaching, remains unclear. Previous research has primarily focused on perceptual aspects rather than on how stereoscopic visual input impacts motor control at the behavioral level. Thus, we investigated the effects of stereoscopic objects in a VR environment on reaching performance, examining whether the stereoscopic effect of objects is a significant aspect enough to affect performance at the behavioral level. While doing so, we investigated young and older adults separately, as age is a critical factor influencing motor performance. Fourteen young and 23 older participants performed a reaching task in the VR space. The target objects were 2D and 3D, deviating from the initial position by 10 and 20 cm. The movement attributed to feedforward control was analyzed using end-point error and smoothness of movement. Our results revealed that older participants had significantly worse predictive control than young participants in the 3D long task, suggesting that the positions of 3D objects were more difficult to predict than those of 2D objects. Young participants showed a significant difference in smoothness between 2D and 3D objects, which was not observed in older participants. This may reflect the floor effect in older participants. Under the short-distance condition, neither group showed a significant difference, suggesting the ceiling effect by distance. We confirmed that the effect of stereoscopic objects was not drastic but it did hamper the reaching performance. [ABSTRACT FROM AUTHOR]

Shoulder exosuits are a promising new technology that could enable individuals with neuromuscular impairments to independently perform activities of daily living, however, scarce evidence exists to evaluate their ability to support such activities. Consequently, it is not understood how humans adapt motion in response to assistance from a shoulder exosuit. In this study, we developed a cable-driven shoulder exosuit and evaluated its effect on reaching and drinking tasks within a cohort of 18 healthy subjects to quantify changes to muscle activity and kinematics as well as trial-to-trial learning in duration and actuator switch timing. The exosuit successfully reduced mean muscle activity in the middle (reaching: 23.4 ± 26.3%, drinking: 20.0 ± 25.1%) and posterior (reaching: 12.8 ± 10.3%, drinking: 4.0 ± 7.2%) deltoid across both functional tasks. Likewise, the exosuit reduced integrated muscle activity in the middle deltoid (reaching: 22.2 ± 22.7%, drinking: 14.9 ± 27.0%). Exosuit assistance also altered kinematics such that individuals allowed their arms to follow forces applied by the exosuit. In terms of learning, subjects reduced movement duration by 15.6 ± 11.9% as they practiced using the exosuit. Reducing movement duration allowed subjects to reduce integrated muscle activity in the anterior (15.2 ± 10.3%), middle (14.7 ± 9.7%), and posterior (14.8 ± 9.7%) deltoids. Similarly, subjects activated the actuator switch earlier over the course of many assisted trials. The muscle activity reductions during both reaching and drinking demonstrate the promise of shoulder exosuits to enable independent function among individuals with neuromuscular impairments. The kinematic response to assistance and learning features observed in movement duration provide insight into human-exosuit interaction principles that could inform future exosuit development. NEW & NOTEWORTHY: Shoulder exosuits assist arm function, but it is not understood how assistance affects motion. We evaluated spatiotemporal movement features and muscle activity during assisted and unassisted arm motions. Introducing the exosuit caused individuals to let their arms follow assistive forces. Furthermore, individuals learned to use the exosuit with practice by moving more quickly to reduce cumulative effort and by activating assistance earlier. These results demonstrate that individuals adapt exosuit-assisted motion to reduce effort. [ABSTRACT FROM AUTHOR]

Incentives tend to drive improvements in performance. But when incentives get too high, we can "choke under pressure" and underperform right when it matters most. What neural processes might lead to choking under pressure? We studied rhesus monkeys performing a challenging reaching task in which they underperformed when an unusually large "jackpot" reward was at stake, and we sought a neural mechanism that might result in that underperformance. We found that increases in reward drive neural activity during movement preparation into, and then past, a zone of optimal performance. We conclude that neural signals of reward and motor preparation interact in the motor cortex (MC) in a manner that can explain why we choke under pressure. [Display omitted] • Rhesus monkeys "choke under pressure" in a difficult reaching task • Neural activity in the motor cortex scales monotonically with reward magnitude • These reward signals adversely interact with movement preparation • This adverse interaction constitutes a neural basis of choking under pressure Why do we "choke under pressure," underperforming when we want to succeed the most? Smoulder et al. identify a neural basis of this paradoxical phenomenon in the motor cortex, where greater rewards influence movement preparatory neural states to be closer to, then farther from, an optimal zone for upcoming movements. [ABSTRACT FROM AUTHOR]

Abstract Background Planning and executing movements requires the integration of different sensory modalities, such as vision and proprioception. However, neurological diseases like stroke can lead to full or partial loss of proprioception, resulting in impaired movements. Recent advances focused on providing additional sensory feedback to patients to compensate for the sensory loss, proving vibrotactile stimulation to be a viable option as it is inexpensive and easy to implement. Here, we test how such vibrotactile information can be integrated with visual signals to estimate the spatial location of a reach target. Methods We used a center-out reach paradigm with 31 healthy human participants to investigate how artificial vibrotactile stimulation can be integrated with visual-spatial cues indicating target location. Specifically, we provided multisite vibrotactile stimulation to the moving dominant arm using eccentric rotating mass (ERM) motors. As the integration of inputs across multiple sensory modalities becomes especially relevant when one of them is uncertain, we additionally modulated the reliability of visual cues. We then compared the weighing of vibrotactile and visual inputs as a function of visual uncertainty to predictions from the maximum likelihood estimation (MLE) framework to decide if participants achieve quasi-optimal integration. Results Our results show that participants could estimate target locations based on vibrotactile instructions. After short training, combined visual and vibrotactile cues led to higher hit rates and reduced reach errors when visual cues were uncertain. Additionally, we observed lower reaction times in trials with low visual uncertainty when vibrotactile stimulation was present. Using MLE predictions, we found that integration of vibrotactile and visual cues followed optimal integration when vibrotactile cues required the detection of one or two active motors. However, if estimating the location of a target required discriminating the intensities of two cues, integration violated MLE predictions. Conclusion We conclude that participants can quickly learn to integrate visual and artificial vibrotactile information. Therefore, using additional vibrotactile stimulation may serve as a promising way to improve rehabilitation or the control of prosthetic devices by patients suffering loss of proprioception.

Abstract Background Children with unilateral cerebral palsy (CP) exhibit motor impairments predominantly on one side of the body, while also having ipsilesional and bilateral impairments. These impairments are known to persist through adulthood, but their extent have not been described in adults with CP. This study’s aim is to characterize bilateral and unilateral upper limbs impairments in adults with CP. Methods Nineteen adults with CP (34.3 years old ± 11.5) performed three robotic assessments in the Kinarm Exoskeleton Lab, including two bilateral tasks (Object Hit [asymmetric independent goals task] and Ball on Bar [symmetric common goal task]) and one unilateral task (Visually Guided Reaching, performed with the more affected arm [MA] and less affected arm [LA]). Individual results were compared to sex, age and handedness matched normative data, describing the proportion of participants exhibiting impairments in each task-specific variable (e.g., Hand speed), each performance category (e.g., Feedforward control) and in global task performance. Associations were assessed using Spearman correlation coefficients between: 1: the results of the MA and LA of each limb in the unilateral task; and 2: the results of each limb in the unilateral vs. the bilateral tasks. Results The majority of participants exhibited impairments in bilateral tasks (84%). The bilateral performance categories (i.e., Bimanual) identifying bilateral coordination impairments were impaired in the majority of participants (Object Hit: 57.8%; Ball on Bar: 31.6%). Most of the participants were impaired when performing a unilateral task with their MA arm (63%) and a smaller proportion with their LA arm (31%). The Feedforward control was the unilateral performance category showing the highest proportion of impaired participants while displaying the strongest relationship between the MA and LA arms impairments (rs = 0.93). Feedback control was the unilateral performance category most often associated with impairments in bilateral tasks (6 out of 8 performance categories). Conclusions Adults with CP experienced more impairment in bilateral tasks while still having substantial impairments in unilateral tasks. They frequently display Feedforward control impairments combined with a higher reliance on Feedback control during both bilateral and unilateral tasks, leading to poorer motor performance.

Background: A rodent autism spectrum disorder (ASD) model based on prenatal exposure to valproic acid (VPA) is widely recognized as a prominent model. Social behavior in rodent ASD models has primarily been evaluated through a three-chamber approach test. However, in this study, we focused on social attention in the VPA model of ASD. Methods: In male C57BL/6 J mice, attentional behaviors toward conspecifics were examined through reaching tasks around 9–11 weeks of age. On embryonic day 12.5, pregnant mice underwent a subcutaneous injection of 600 mg/kg VPA sodium salt dissolved in 0.9% saline solution (VPA group) or saline solution alone (Sal group) into their neck fat. Thirty-six mice—nine each in the VPA and saline groups, and 18 partners—underwent training in reaching behavior. Subsequently, we examined whether the VPA or Sal group demonstrated focused attention toward their partners during reaching tasks. A two-way analysis of variance (ANOVA) (condition [VPA/Sal] × situation [face-to-face (attention)/not paying attention (not attention)]) was conducted on the average success rate of the situation. Additionally, we measured the duration of sniffing behavior between pairs of mice in an open field twice in total at 4 and 8 weeks of age before reaching task. The pairs were constructed by pairing a VPA or Sal group mouse with its partner, with the objective of facilitating initial encounters between the mice. A one-way ANOVA was conducted on the average duration of sniffing behavior data from 4 weeks and a second one-way ANOVA on data from 8 weeks. Results: The analysis revealed a significant interaction between condition and situation in the reaching task [F (1, 28) = 6.75, p = 0.015, ηp² = 0.19]. The simple main effect test exhibited that the “not paying attention” rate was significantly higher than that of the “face-to-face” in the VPA group (p < 0.01). The results revealed a not significant difference in the average duration of sniffing behavior at 4 weeks [F (3, 32) = 2.71, p = 0.06, n.s., ηp² = 0.20], but significant difference at 8 weeks [F (3, 32) = 4.12, p < 0.05, ηp² = 0.28]. Multiple comparisons using the Bonferroni method revealed significant differences in the sniffing duration at 8 weeks between from the partner toward the VPA mouse and from the partner toward the Sal mouse (p < 0.05). Conclusion: The VPA rodent model of ASD exhibited differences in social attention compared to the saline group. By focusing on social attention and exploring various ASD models, insights can be gained from the neural mechanisms underlying gaze abnormalities during social interaction in individuals with ASD. [ABSTRACT FROM AUTHOR]

Background: Planning and executing movements requires the integration of different sensory modalities, such as vision and proprioception. However, neurological diseases like stroke can lead to full or partial loss of proprioception, resulting in impaired movements. Recent advances focused on providing additional sensory feedback to patients to compensate for the sensory loss, proving vibrotactile stimulation to be a viable option as it is inexpensive and easy to implement. Here, we test how such vibrotactile information can be integrated with visual signals to estimate the spatial location of a reach target. Methods: We used a center-out reach paradigm with 31 healthy human participants to investigate how artificial vibrotactile stimulation can be integrated with visual-spatial cues indicating target location. Specifically, we provided multisite vibrotactile stimulation to the moving dominant arm using eccentric rotating mass (ERM) motors. As the integration of inputs across multiple sensory modalities becomes especially relevant when one of them is uncertain, we additionally modulated the reliability of visual cues. We then compared the weighing of vibrotactile and visual inputs as a function of visual uncertainty to predictions from the maximum likelihood estimation (MLE) framework to decide if participants achieve quasi-optimal integration. Results: Our results show that participants could estimate target locations based on vibrotactile instructions. After short training, combined visual and vibrotactile cues led to higher hit rates and reduced reach errors when visual cues were uncertain. Additionally, we observed lower reaction times in trials with low visual uncertainty when vibrotactile stimulation was present. Using MLE predictions, we found that integration of vibrotactile and visual cues followed optimal integration when vibrotactile cues required the detection of one or two active motors. However, if estimating the location of a target required discriminating the intensities of two cues, integration violated MLE predictions. Conclusion: We conclude that participants can quickly learn to integrate visual and artificial vibrotactile information. Therefore, using additional vibrotactile stimulation may serve as a promising way to improve rehabilitation or the control of prosthetic devices by patients suffering loss of proprioception. [ABSTRACT FROM AUTHOR]

Reaching movements can be redirected during their progress to handle unexpected visual changes, such as a change in target location. It is important to know when these redirections start, i.e., the online reaction time (oRT), but this information is not readily evident since redirections are embedded within a time-varying baseline movement that differs from trial to trial. The one previous study that evaluated the performance of different oRT identification methods utilized simulated redirections with the exact same onset, rather than a range of onsets as would be typically encountered. We addressed this gap by utilizing batches of "hybrid" trials with temporal spread in their oRTs. Each hybrid trial combined a sampled baseline movement with an idealized corrective response. Two new methods had the most accurate identification of online reaction times: 1) a threshold-aligned grand mean regression, and 2) a template-based approach we term the canonical correction search. The threshold-aligned grand mean regression is simple to implement and effective. The canonical correction search is a more complex procedure but arguably better linked to the underlying response. Applying the two methods to a published dataset revealed more delayed oRTs than was previously reported along with new information such as the width of oRT distributions. Taken together, our results demonstrate the utility of two new methods for dissecting corrective action from ongoing movement. NEW & NOTEWORTHY: Advancing our understanding of visual feedback control requires methods that accurately identify the onset of corrective action. We developed a modified regression approach and a template-based approach to identify the online reaction time of single-reaching movements. Both outperform previous methods when challenged by temporal jitter in the response onset and increased background noise. [ABSTRACT FROM AUTHOR]

The motor impairments experienced by people with Parkinson's disease (PD) are exacerbated during memory‐guided movements. Despite this, the effect of antiparkinson medication on memory‐guided movements has not been elucidated. We evaluated the effect of antiparkinson medication on motor control during a memory‐guided reaching task with short and long retention delays in participants with PD and compared performance to age‐matched healthy control (HC) participants. Thirty‐two participants with PD completed the motor section of the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS‐UPDRS III) and performed a memory‐guided reaching task with two retention delays (0.5 s and 5 s) while on and off medication. Thirteen HC participants completed the MDS‐UPDRS III and performed the memory‐guided reaching task. In the task, medication increased movement velocity, decreased movement time, and decreased reaction time toward what was seen in the HC. However, movement amplitude and reaching error were unaffected by medication. Shorter retention delays increased movement velocity and amplitude, decreased movement time, and decreased error, but increased reaction times in the participants with PD and HC. Together, these results imply that antiparkinson medication is more effective at altering the neurophysiological mechanisms controlling movement velocity and reaction time compared with other aspects of movement control. [ABSTRACT FROM AUTHOR]

In daily life tasks of the upper limb, we must make quick corrections with our hands in unstable postural situations. Postural and reaching control mechanisms are involved in the accurate execution of upper-limb tasks. This research aimed to determine the effect of different postural stability conditions on the motor performance of the upper limb in a reaching task with non-static targets. 19 young participants performed a reaching task toward targets that exhibited a change in position (at 200 or 600 ms) in different postural conditions (bipedal-firm, bipedal-foam, and unipedal-foam surface). Performance on the screen (motion time and spatial error), balance (center of pressure displacements, CoP), and index finger movements were recorded during the reaching task. The instability affects the finger kinematic (displacements) and CoP kinematic (displacements, speed, and smoothness) without affecting the performance on the screen (precision and duration). The timing of target change affects the performance on the screen, finger kinematic (speed and smoothness), and CoP kinematic (displacements, speed, and smoothness). Postural and reaching control systems enable accurate hand motions in less stable situations, even in reaching tasks with non-static targets. The postural and reaching control systems can protect the end-effector performance during unstable conditions but not during trials with less time to correct the motion. • Postural instability does not affect the finger performance on the screen of non-static reaching. • Postural instability affects the finger and CoP kinematics during non-static reaching. • The timing of target change affects the performance of reaching and body kinematics. • Postural and reaching control systems can protect finger performance on the screen during unstable conditions. • Postural and reaching control systems cannot protect finger performance on the screen with little time to correct. [ABSTRACT FROM AUTHOR]

This study examined the co‐development of infant reaching and postural control across the transition to arms‐free sitting at home. We observed infants with typical likelihood (TL; n = 24) and elevated likelihood (EL; n = 20) for autism at four biweekly sessions spanning the transition to arms‐free sitting (infant age = 4.5–8 months at first session). At each session, infants sat on a pressure‐sensitive mat with external support or independently, wore magneto‐inertial sensors on both wrists, and reached for toys presented at midline. Analyses focused on characterizing and comparing control of sitting during reaching actions and standard kinematic metrics of reaching during Supported versus Independent Sitting. Although EL infants achieved arms‐free sitting later than TL peers, there were no group differences on any measures. Across sessions, infants' control of the sitting posture during concurrent reaching movements improved in both contexts, though they were less stable as they reached when sitting independently compared to when sitting with support. A similar effect was apparent in the kinematics of reaches, with overall improvement over time, but evidence of poorer control in Independent relative to Supported Sitting. Taken together, these findings underscore the mutually influential and dynamic relations between emerging skills and well‐established behaviors. [ABSTRACT FROM AUTHOR]

Background: Children with unilateral cerebral palsy (CP) exhibit motor impairments predominantly on one side of the body, while also having ipsilesional and bilateral impairments. These impairments are known to persist through adulthood, but their extent have not been described in adults with CP. This study's aim is to characterize bilateral and unilateral upper limbs impairments in adults with CP. Methods: Nineteen adults with CP (34.3 years old ± 11.5) performed three robotic assessments in the Kinarm Exoskeleton Lab, including two bilateral tasks (Object Hit [asymmetric independent goals task] and Ball on Bar [symmetric common goal task]) and one unilateral task (Visually Guided Reaching, performed with the more affected arm [MA] and less affected arm [LA]). Individual results were compared to sex, age and handedness matched normative data, describing the proportion of participants exhibiting impairments in each task-specific variable (e.g., Hand speed), each performance category (e.g., Feedforward control) and in global task performance. Associations were assessed using Spearman correlation coefficients between: 1: the results of the MA and LA of each limb in the unilateral task; and 2: the results of each limb in the unilateral vs. the bilateral tasks. Results: The majority of participants exhibited impairments in bilateral tasks (84%). The bilateral performance categories (i.e., Bimanual) identifying bilateral coordination impairments were impaired in the majority of participants (Object Hit: 57.8%; Ball on Bar: 31.6%). Most of the participants were impaired when performing a unilateral task with their MA arm (63%) and a smaller proportion with their LA arm (31%). The Feedforward control was the unilateral performance category showing the highest proportion of impaired participants while displaying the strongest relationship between the MA and LA arms impairments (rs = 0.93). Feedback control was the unilateral performance category most often associated with impairments in bilateral tasks (6 out of 8 performance categories). Conclusions: Adults with CP experienced more impairment in bilateral tasks while still having substantial impairments in unilateral tasks. They frequently display Feedforward control impairments combined with a higher reliance on Feedback control during both bilateral and unilateral tasks, leading to poorer motor performance. [ABSTRACT FROM AUTHOR]

Precision reaching often requires corrective submovements to obtain the desired goal. Most studies of reaching have focused on single initial movements, and implied the cortical encoding model was the same for all submovements. However, corrective submovements may show different encoding patterns from the initial submovement with distinct patterns of activation across the population. Two rhesus macaques performed a precision center-out-task with small targets. Neural activity from single units in the primary motor cortex and associated behavioral data were recorded to evaluate movement characteristics. Neural population data and individual neuronal firing rates identified with a peak finding algorithm to identify peaks in hand speed were examined for encoding differences between initial and corrective submovements. Individual neurons were fitted with a regression model that included the reach vector, position, and speed to predict firing rate. For both initial and corrective submovements, the largest effect remained movement direction. We observed a large subset changed their preferred direction greater than 45° between initial and corrective submovements. Neuronal depth of modulation also showed considerable variation when adjusted for movement speed. By using principal component analysis, neural trajectories of initial and corrective submovements progressed through different neural subspaces. These findings all suggest that different neural encoding patterns exist for initial and corrective submovements within the cortex. We hypothesize that this variation in how neurons change to encode small, corrective submovements might allow for a larger portion of the neural space being used to encode a greater range of movements with varying amplitudes and levels of precision. NEW & NOTEWORTHY: Neuronal recordings matched with kinematic behavior were collected in a precision center-out task that often required corrective movements. We reveal large differences in preferred direction and depth of modulation between initial and corrective submovements across the neural population. We then present a model of the neural population describing how these shifts in tuning create different subspaces for signaling initial and corrective movements likely to improve motor precision. [ABSTRACT FROM AUTHOR]

Following events such as fatigue or stroke, individuals often move their trunks forward during reaching, leveraging a broader muscle group even when only arm movement would suffice. In previous work, we showed the existence of a "force reserve": a phenomenon where individuals, when challenged with a heavy weight, adjusted their motor coordination to preserve approximately 40% of their shoulder's force. Here, we investigated if such reserve can predict hip, shoulder, and elbow movements and torques resulting from an induced shoulder strength deficit. We engaged 20 healthy participants in a reaching task with incrementally heavier dumbbells, analyzing arm and trunk movements via motion capture and joint torques through inverse dynamics. We simulated these movements using an optimal control model of a 3-degree-of-freedom upper body, contrasting three cost functions: traditional sum of squared torques, a force reserve function incorporating a nonlinear penalty, and a normalized torque function. Our results demonstrate a clear increase in trunk movement correlated with heavier dumbbell weights, with participants employing compensatory movements to maintain a shoulder force reserve of approximately 40% of maximum torque. Simulations showed that while traditional and reserve functions accurately predicted trunk compensation, only the reserve function effectively predicted joint torques under heavier weights. These findings suggest that compensatory movements are strategically employed to minimize shoulder effort and distribute load across multiple joints in response to weakness. We discuss the implications of the force reserve cost function in the context of optimal control of human movements and its relevance for understanding compensatory movements poststroke. NEW & NOTEWORTHY: Our study reveals key findings on compensatory movements during upper limb reaching tasks under shoulder strength deficits, as observed poststroke. Using heavy dumbbells with healthy volunteers, we demonstrate how forward trunk displacement conserves around 40% of shoulder strength reserve during reaching. We show that an optimal controller employing a cost function combining squared motor torque and a nonlinear penalty for excessive muscle activation outperforms traditional controllers in predicting torques and compensatory movements in these scenarios. [ABSTRACT FROM AUTHOR]

The handshake is the most acceptable gesture of greeting in many cultures throughout many centuries. To date, robotic arms are not capable of fully replicating this typical human gesture. Using multiple sensors that detect contact forces and displacements, we characterized the movements that occurred during handshakes. A typical human-to- human handshake took around 3.63 s (SD = 0.45 s) to perform. It can be divided into three phases: reaching (M = 0.92 s, SD = 0.45 s), contact (M = 1.96 s, SD = 0.46 s), and return (M = 0.75 s, SD = 0.12 s). The handshake was further investigated to understand its subtle movements. Using a multiphase jerk minimization model, a smooth human-to- human handshake can be modelled with fifth or fourth degree polynomials at the reaching and return phases, and a sinusoidal function with exponential decay at the contact phase. We show that the contact phase (1.96 s) can be further divided according to the following subphases: preshake (0.06 s), main shake (1.31 s), postshake (0.06 s), and a period of no movement (0.52 s) just before both hands are retracted. We compared these to the existing handshake models that were proposed for physical human-robot interaction (pHRI). From our findings in human-to-human handshakes, we proposed guidelines for a more natural handshake movement between humanoid robots and their human partners. [ABSTRACT FROM AUTHOR]

Prism adaptation (PA) affects visuospatial attention such as spatial orienting in both the right and left hemifields; however, the systematic after-effects of PA on visuospatial attention remain unclear. Visuospatial attention can be affected by non-spatial attentional factors, and postural control difficulty, which delays the reaction time (RT) to external stimulation, may be one such factor. Therefore, we aimed to investigate the influence of postural control difficulty on changes in spatial orienting of attention after leftward PA. Seventeen healthy young adults underwent 15-min and 5-min PA procedures for a leftward visual shift (30 diopters). Participants underwent the Posner cueing test immediately before (pre-evaluation) and in between and after the PA procedures (post-evaluations) while standing barefoot on the floor (normal standing condition) and on a balance-disc (balance standing condition). In the pre-evaluation, RTs in the balance standing condition were significantly longer compared to those in the normal standing condition for targets appearing in both the right and left hemifields. Leftward PA improved the RT for targets appearing in the right, but no left, hemifield in the balance standing condition, such that RTs for targets in the right hemifield in the post-evaluation were not significantly different between the two standing conditions. However, leftward PA did not significantly change RTs for targets in both hemifields in the normal standing condition. Therefore, postural control difficulty may enhance sensitivity to the features of the visuospatial cognitive after-effects of leftward PA. [ABSTRACT FROM AUTHOR]

Although the stereoscopic effect in 3D virtual reality (VR) space has been studied, its influence on motor performance, specifically how stereoscopic objects affect behavioral outcomes like reaching, remains unclear. Previous research has primarily focused on perceptual aspects rather than on how stereoscopic visual input impacts motor control at the behavioral level. Thus, we investigated the effects of stereoscopic objects in a VR environment on reaching performance, examining whether the stereoscopic effect of objects is a significant aspect enough to affect performance at the behavioral level. While doing so, we investigated young and older adults separately, as age is a critical factor influencing motor performance. Fourteen young and 23 older participants performed a reaching task in the VR space. The target objects were 2D and 3D, deviating from the initial position by 10 and 20 cm. The movement attributed to feedforward control was analyzed using end-point error and smoothness of movement. Our results revealed that older participants had significantly worse predictive control than young participants in the 3D long task, suggesting that the positions of 3D objects were more difficult to predict than those of 2D objects. Young participants showed a significant difference in smoothness between 2D and 3D objects, which was not observed in older participants. This may reflect the floor effect in older participants. Under the short-distance condition, neither group showed a significant difference, suggesting the ceiling effect by distance. We confirmed that the effect of stereoscopic objects was not drastic but it did hamper the reaching performance.

Abstract Background Movement smoothness is a potential kinematic biomarker of upper extremity (UE) movement quality and recovery after stroke; however, the measurement properties of available smoothness metrics have been poorly assessed in this group. We aimed to measure the reliability, responsiveness and construct validity of several smoothness metrics. Methods This ancillary study of the REM-AVC trial included 31 participants with hemiparesis in the subacute phase of stroke (median time since stroke: 38 days). Assessments performed at inclusion (Day 0, D0) and at the end of a rehabilitation program (Day 30, D30) included the UE Fugl Meyer Assessment (UE-FMA), the Action Research Arm Test (ARAT), and 3D motion analysis of the UE during three reach-to-point movements at a self-selected speed to a target located in front at shoulder height and at 90% of arm length. Four smoothness metrics were computed: a frequency domain smoothness metric, spectral arc length metric (SPARC); and three temporal domain smoothness metrics (TDSM): log dimensionless jerk (LDLJ); number of submovements (nSUB); and normalized average rectified jerk (NARJ). Results At D30, large clinical and kinematic improvements were observed. Only SPARC and LDLJ had an excellent reliability (intra-class correlation > 0.9) and a low measurement error (coefficient of variation 0.8) and not to changes in movement straightness (non-significant correlations). Most construct validity hypotheses tested were verified except for TDSM with low correlations with clinical metrics at D0 (rSpearman

Previous studies suggest that bimanual coordination recruits neural mechanisms that explicitly couple control of the arms, resulting in symmetric kinematics. However, the higher symmetry for actions that require congruous joint motions compared with noncongruous joint motions calls into question the concept of control coupling as a general policy. An alternative view proposes that codependence might emerge from an optimal feedback controller that minimizes control effort and costs in task performance. Support for this view comes from studies comparing conditions in which both hands move a shared or independent virtual objects. Because these studies have mainly focused on congruous bimanual movements, it remains unclear if kinematic symmetry emerges from such control policies. We now examine movements with congruous or noncongruous joint motions (inertially symmetric or asymmetric, respectively) under shared or independent cursors conditions. We reasoned that if a control policy minimizes kinematic differences between limbs, spatiotemporal symmetry should remain relatively unaffected by inertial asymmetries. As shared tasks reportedly elicit greater interlimb codependence, these conditions should elicit higher bilateral covariance regardless of inertial asymmetries. Our results indicate a robust spatiotemporal symmetry only under inertially symmetric conditions, regardless of cursor condition. We simulated bimanual reaching using an optimal feedback controller with and without explicit costs of kinematic asymmetry, finding that only the latter mirrored our empirical data. Our findings support the hypothesis that bimanual control policies do not include kinematic asymmetry as a cost when it is not demanded by task constraints suggesting that kinematic symmetry depends critically on mechanical movement conditions. NEW & NOTEWORTHY: Previously, the control coupling hypothesis and task-dependent control hypothesis have been shown to be robust in the bimanually symmetrical movement, but whether the same policy remains robust in the bimanually asymmetrical movement remains unclear. Here, with evidence from empirical and simulation data, we show that a spatiotemporal symmetry between the arms is not predicated on control coupling, but instead it is predicated on the symmetry of mechanical conditions (e.g. limb inertia) between the arms. [ABSTRACT FROM AUTHOR]

Recent work showed that individuals with cerebellar degeneration could leverage intact reinforcement learning (RL) to alter their movement. However, there was marked inter-individual variability in learning, and the factors underlying it were unclear. Cerebellum-dependent sensory prediction may contribute to RL in motor contexts by enhancing body state estimates, which are necessary to solve the credit-assignment problem. The objective of this study was to test the relationship between the predictive component of state estimation and RL in individuals with cerebellar degeneration. Individuals with cerebellar degeneration and neurotypical control participants completed two tasks: an RL task that required them to alter the angle of reaching movements and a state estimation task that tested the somatosensory perception of active and passive movement. The state estimation task permitted the calculation of the active benefit shown by each participant, which is thought to reflect the cerebellum-dependent predictive component of state estimation. We found that the cerebellar and control groups showed similar magnitudes of learning with reinforcement and active benefit on average, but there was substantial variability across individuals. Using multiple regression, we assessed potential predictors of RL. Our analysis included active benefit, somatosensory acuity, clinical ataxia severity, movement variability, movement speed, and age. We found a significant relationship in which greater active benefit predicted better learning with reinforcement in the cerebellar, but not the control group. No other variables showed significant relationships with learning. Overall, our results support the hypothesis that the integrity of sensory prediction is a strong predictor of RL after cerebellar damage. [ABSTRACT FROM AUTHOR]

Background: Movement smoothness is a potential kinematic biomarker of upper extremity (UE) movement quality and recovery after stroke; however, the measurement properties of available smoothness metrics have been poorly assessed in this group. We aimed to measure the reliability, responsiveness and construct validity of several smoothness metrics. Methods: This ancillary study of the REM-AVC trial included 31 participants with hemiparesis in the subacute phase of stroke (median time since stroke: 38 days). Assessments performed at inclusion (Day 0, D0) and at the end of a rehabilitation program (Day 30, D30) included the UE Fugl Meyer Assessment (UE-FMA), the Action Research Arm Test (ARAT), and 3D motion analysis of the UE during three reach-to-point movements at a self-selected speed to a target located in front at shoulder height and at 90% of arm length. Four smoothness metrics were computed: a frequency domain smoothness metric, spectral arc length metric (SPARC); and three temporal domain smoothness metrics (TDSM): log dimensionless jerk (LDLJ); number of submovements (nSUB); and normalized average rectified jerk (NARJ). Results: At D30, large clinical and kinematic improvements were observed. Only SPARC and LDLJ had an excellent reliability (intra-class correlation > 0.9) and a low measurement error (coefficient of variation < 10%). SPARC was responsive to changes in movement straightness (rSpearman=0.64) and to a lesser extent to changes in movement duration (rSpearman=0.51) while TDSM were very responsive to changes in movement duration (rSpearman>0.8) and not to changes in movement straightness (non-significant correlations). Most construct validity hypotheses tested were verified except for TDSM with low correlations with clinical metrics at D0 (rSpearman<0.5), ensuing low predictive validity with clinical metrics at D30 (non-significant correlations). Conclusions: Responsiveness and construct validity of TDSM were hindered by movement duration and/or noise-sensitivity. Based on the present results and concordant literature, we recommend using SPARC rather than TDSM in reaching movements of uncontrolled duration in individuals with spastic paresis after stroke. Trial Registration: NCT01383512, https://clinicaltrials.gov/, June 27, 2011. Highlights: Reliability, responsiveness and construct validity of SPARC were satisfactory. Responsiveness and construct validity of LDLJ, NARJ and nSUB were highly related to movement duration. LDLJ had an excellent reliability and a low measurement error, but not NARJ and nSUB. [ABSTRACT FROM AUTHOR]

Despite recent studies indicating a significant correlation between somatosensory deficits and rehabilitation outcomes, how prevailing somatosensory deficits affect stroke survivors' ability to correct their movements and recover overall remains unclear. To explore how major deficits in somatosensory systems impede stroke survivors' motor correction to various external loads, we conducted a study with 13 chronic stroke survivors who had hemiparesis. An inertial, elastic, or viscous load, which was designed to impose perturbing forces with various force profiles, was introduced unexpectedly during the reaching task using a programmable haptic robot. Participants' proprioception and cutaneous sensation were also assessed using passive movement detection, finger-to-nose, mirror, repositioning, and Weinstein pressure tests. These measures were then analyzed to determine whether the somatosensory measures significantly correlated with the estimated reaching performance parameters, such as initial directional error, positional deviation, velocity deviations, and speed of motor correction were measured. Of 13 participants, 5 had impaired proprioception, as they could not recognize the passive movement of their elbow joint, and they kept showing larger initial directional errors even after the familiarization block. Such continuously found inaccurate initial movement direction might be correlated with the inability to develop the spatial body map especially for calculating the initial joint torques when starting the reaching movement. Regardless of whether proprioception was impaired or not, all participants could show the stabilized, constant reaching movement trajectories. This highlights the role of proprioception especially in the execution of a planned movement at the early stage of reaching movement. [ABSTRACT FROM AUTHOR]

When carrying out a sequence of movements, humans can plan several steps in advance to make the movement smooth.

Real-world actions often comprise a series of movements that cannot be entirely planned before initiation. When these actions are executed rapidly, the planning of multiple future movements needs to occur simultaneously with the ongoing action. How the brain solves this task remains unknown. Here, we address this question with a new sequential arm reaching paradigm that manipulates how many future reaches are available for planning while controlling execution of the ongoing reach. We show that participants plan at least two future reaches simultaneously with an ongoing reach. Further, the planning processes of the two future reaches are not independent of one another. Evidence that the planning processes interact is twofold. First, correcting for a visual perturbation of the ongoing reach target is slower when more future reaches are planned. Second, the curvature of the current reach is modified based on the next reach only when their planning processes temporally overlap. These interactions between future planning processes may enable smooth production of sequential actions by linking individual segments of a long sequence at the level of motor planning.

Adaptive motor behavior depends on the coordinated activity of multiple neural systems distributed across the brain. While the role of sensorimotor cortex in motor learning has been well established, how higher-order brain systems interact with sensorimotor cortex to guide learning is less well understood. Using functional MRI, we examined human brain activity during a reward-based motor task where subjects learned to shape their hand trajectories through reinforcement feedback. We projected patterns of cortical and striatal functional connectivity onto a low-dimensional manifold space and examined how regions expanded and contracted along the manifold during learning. During early learning, we found that several sensorimotor areas in the dorsal attention network exhibited increased covariance with areas of the salience/ventral attention network and reduced covariance with areas of the default mode network (DMN). During late learning, these effects reversed, with sensorimotor areas now exhibiting increased covariance with DMN areas. However, areas in posteromedial cortex showed the opposite pattern across learning phases, with its connectivity suggesting a role in coordinating activity across different networks over time. Our results establish the neural changes that support reward-based motor learning and identify distinct transitions in the functional coupling of sensorimotor to transmodal cortex when adapting behavior.

Attention is needed to perform goal-directed vision-guided movements. We investigated whether the direction of covert attention modulates movement outcomes and dynamics. Right-handed and left-handed volunteers attended to a spatial location while planning a reach toward the same hemifield, the opposite one, or planned a reach without constraining attention. We measured behavioral variables as outcomes of ipsilateral and contralateral reaching and the tangling of behavioral trajectories obtained through principal component analysis as a measure of the dynamics of motor control. We found that the direction of covert attention had significant effects on the dynamics of motor control, specifically during contralateral reaching. Data suggest that motor control was more feedback-driven when attention was directed leftward than when attention was directed rightward or when it was not constrained, irrespectively of handedness. These results may help to better understand the neural bases of asymmetrical neurological diseases like hemispatial neglect.

Conventionally, the adaptive body area for prism adaptation (PA) has been limited to the visible area of prism glasses, especially the unilateral upper limbs. In this study, we developed a virtual reality system that extends PA's adaptive body area. This system sets the visible area of the target and introduces a symbolic representation of the body position to realize a head position adaptation task. As a result, the develped system generates PA not to individual body parts but to a collection of multiple motor units. Furthermore, experimental results in healthy subjects showed that the head position adaptation task could generate PA in the upper trunk system (The upper trunk system is defined as a system consisting of the upper trunk, head, and upper extremities) and displace it to the left anteriorly. Therefore, the head position adaptation task is expected to be effective for the postural correction of USN patients with upper trunk system tilt to the right posteriorly. Moreover, the developed system has potential applications in a wide range of fields, such as detecting cerebellar disorders. [ABSTRACT FROM AUTHOR]

A defining feature of most primates is a hand with five fingers. Spider monkeys are an exception because they have four fingers and no thumb. Despite the prevalence of reach-to-grasp research in primates, it is not known how the lack of a thumb affects reaching and grasping in spider monkeys. Drawing on patterns that have been well described in human adults, human infants, and other nonhuman primates, this study characterized prehension in Colombian spider monkeys (Ateles fusciceps rufiventris). Monkeys reached for two differently sized food objects and reaches were digitized offline for two-dimensional kinematic analysis. Grasp strategy was coded from video as preshaped when the hand was adjusted to grasp the food before contact, or not preshaped when the hand was adjusted to grasp the food after contact. Monkeys exhibited variability in reach smoothness that contrasted with the typical pattern seen in other adult primates and instead resembled the pattern observed in human infants. Monkeys anticipated the object to be grasped approximately half of the time. Reaches where the hand was preshaped to the object were smoother than reaches where the hand was adjusted to grasp after object contact. For the small object, reaches with preshaping were straighter than reaches without preshaping. Results are the first evidence of kinematic signatures for reach-to-grasp actions in spider monkeys. [ABSTRACT FROM AUTHOR]

Background and Objective: Upper extremity impairment is one of the complications in hemiplegic children. The purpose of modified constraint‐induced movement therapy (mCIMT) is to improve the function of impaired arms and hands in these children. This study compared the efficacy of mCIMT and the approach of neurodevelopmental therapy (NDT) on reaching capacity in children with spastic hemiplegia. Methods: Fifty‐two spastic hemiplegic children ranging in age from four to 6 years were selected for this study from an outpatient clinic and biomechanical lab (Prince Sattam bin Abdulaziz University, KSA). They were randomly divided into two experimental groups: group I received NDT and group II received mCIMT for the involved upper limb and restriction of the uninvolved arm movements for 12 weeks (three times per week). Both groups received a conventional exercise program in addition to experimental one. Active elbow extension range of motion and three‐dimensional motion analysis of the reaching task were measured before and after 3 months of treatment. Results: Significant enhancement in all pre‐treatment and post‐treatment outcomes was observed in both groups by a two‐way mixed MANOVA; furthermore, Group II (mCIMT) showed the most significant improvement (elbow extension, percentage of reach to peak velocity, movement time and movement units) when comparing the post‐treatment outcomes between the two groups (p < 0.001). Implication for Physiotherapy Practice: Addition of mCIMT to a conventional exercise was superior to adding NDT exercise therapy in promoting the performance of reaching pattern in hemiplegic children. [ABSTRACT FROM AUTHOR]

This study departs from the conventional research on horizontal plane reach movements by examining human motor control strategies in vertical plane elastic load reach movements conducted without visual feedback. Here, participants performed shoulder presses with elastic resistances at low, moderate, and high intensities without access to visual information about their hand position, relying exclusively on proprioceptive feedback and synchronizing their movements with a metronome set at a 3 s interval. The results revealed consistent performance symmetry across different intensities in terms of the reach speed (p = 0.254–0.736), return speed (p = 0.205–0.882), and movement distance (p = 0.480–0.919). This discovery underscores the human capacity to uphold bilateral symmetry in movement execution when relying solely on proprioception. Furthermore, this study observed an asymmetric velocity profile where the reach duration remained consistent irrespective of the load (1.15 s), whereas the return duration increased with higher loads (1.39 s–1.45 s). These findings suggest that, in the absence of visual feedback, the asymmetric velocity profile does not result from the execution of the action but rather represents a deliberate deceleration post-reach aimed at achieving the target position as generated by the brain's internal model. These findings hold significant implications for interpreting rehabilitation approaches under settings devoid of visual feedback. [ABSTRACT FROM AUTHOR]

Previous studies showed numerous evidence for the interlimb asymmetries in motor performance during arm reaching movements. Furthermore, these interlimb asymmetries have been shown to associate with spatial patterns of hand selection behavior. Importantly, these interlimb asymmetries can be modified systematically by occlusion of visual feedback, or a long-term sports training. In this study, we asked about the effects of a short-term training on interlimb asymmetries. Eighteen healthy young participants underwent a 12-week novice traditional archery training (TAT). Their unimanual dominant and nondominant arm reaching movement performance was assessed before and after TAT. We found that movement accuracy, movement precision, and movement efficiency in the experimental group have all improved significantly as a result of TAT. These improvements were comparable across both arms, thus the interlimb differences in movement performance were not affected by the short-term TAT and remained similar. These results suggest that while short-term training may contribute positively to reaching performance, it is unlikely to have a significant impact on the differences observed between the dominant and nondominant arms. This unique characteristics of dominant and nondominant arm should be taken into consideration when developing targeted sports and rehabilitation programs for athletes or individuals with acute or chronic motor deficits. [ABSTRACT FROM AUTHOR]

BACKGROUND: Stroke often causes impairments in goal-directed movements, which are commonly assessed using goal-directed reaching tasks. Here we present two individuals poststroke who performed two robotic reaching tasks: 1. Visually Guided Reaching (VGR); reaching a cursor representing the fingertip to virtual targets, 2. Reverse Visually Guided Reaching (RVGR); where the cursor moves in the opposite direction of hand motion, requiring a novel cognitive rule. Participants are typically more successful at reaching targets in the simple VGR task compared to the more complex RVGR task (~92% of our database). The two cases are notable as they performed better on RVGR compared to VGR. CASE DESCRIPTIONS: Case 1: 80-year-old patient with left hemorrhagic thalamic stroke, with interventricular extension, presenting with right hemiparesis/reduced motor control. They were unable to complete reaches to any targets in VGR (0/40 targets), but were able to reach ~30% of the targets (15/48) in RVGR. Case 2: 76-year-old patient with a left ischemic pontine stroke, presenting with right hemiparesis/reduced motor control. They were unable to complete reaches to any targets in VGR (0/40) but were able to reach ~60% of the targets in RVGR (29/48). INTERPRETATION: Better performance in RVGR compared to VGR may be associated with a "dual-task benefit" and has potential clinical implications, including informing neuro-rehabilitative strategies, potentially by including tasks with added complexity or cognitive components. These findings also highlight the utility of robotic tools to provide novel environments within which to identify unique patterns of impairments and abilities. [ABSTRACT FROM AUTHOR]