Hand preference trajectories as predictors of language outcomes above and beyond SES: Infant patterns explain more variance than toddler patterns at 5 years of age.

Prior studies found hand preference trajectories predict preschool language outcomes. However, this approach has been limited to examining bimanual manipulation in toddlers. It is not known whether hand preference during infancy for acquiring objects (i.e., reach-to-grasp) similarly predicts childhood language ability. The current study explored this motor-language developmental cascade in 90 children. Hand preference for acquiring objects was assessed monthly from 6 to 14 months and language skill was assessed at 5 years. Latent class growth analysis identified three infant hand preference classes: left, early right, and late right. Infant hand preference classes predicted 5-year language skills. Children in the left and early right classes, who were categorized as having a consistent hand preference, had higher expressive and receptive language scores relative to children in the inconsistent late right class. Consistent classes did not differ from each other on language outcomes. Infant hand preference patterns explained more variance for expressive and receptive language relative to previously reported toddler hand preference patterns, above and beyond socioeconomic status (SES). Results suggest that hand preference, measured at different time points across development using a trajectory approach, is reliably linked to later language.

Time-independent relationship between digits closure velocity and hand transport acceleration during reach-to-grasp movements.

Prehension movements in primates have been extensively studied for decades, and hand transport and hand grip adjustment are usually considered as the main components of any object reach-to-grasp action. Evident temporal patterns were found for the velocity of the hand during the transport phase and for the digits kinematics during pre-shaping and enclosing phases. However, such kinematics were always analysed separately in regard to time, and never studied in terms of dependence one from another. Nevertheless, if a reliable one-to-one relationship is proven, it would allow reconstructing the digit velocity (and position) simply by knowing the hand acceleration during reaching motions towards the target object, ceasing the usual dependence seen in literature from time of movement and distance from the target. In this study, the aim was precisely to analyse reach-to-grasp motions to explore if such relationship exists and how it can be formulated. Offline and real-time results not only seem to suggest the existence of a time-independent, one-to-one relationship between hand transport and hand grip adjustment, but also that such relationship is quite resilient to the different intrinsic and extrinsic properties of the target objects such as size, shape and position.

Post-error adjustments occur in both reaching and grasping.

Post-error slowing (PES), the tendency to slow down a behavioral response after a previous error, has typically been investigated during simple cognitive tasks using response time as a measure of PES magnitude. More recently, PES was investigated during a single reach-to-grasp task to determine where post-error adjustments are employed in a more ecological setting. Kinematic analyses in the previous study detected PES during pre-movement planning and within the grasping component of movement execution. In the current study (N = 22), we increased the cognitive demands of a reach-to-grasp task by adding a choice between target and distractor locations to further explore PES, and other post-error adjustments, under different task conditions. We observed a significant main effect of task condition on overall reaction time (RT); however, it did not significantly impact PES or other post-error adjustments. Nonetheless, the results of this study suggest post-error adjustment is a flexible process that can be observed during pre-movement planning and within the onset and magnitude of the reaching component, as well as in the magnitudes of the grasping component. Considering the sum of the results in the context of existing literature, we conclude that the findings add support to a functional account of error reactivity, such that post-error adjustments are implemented intentionally to improve performance.

Neuritogenic glycosaminoglycan hydrogels promote functional recovery after severe traumatic brain injury.

Objective.Severe traumatic brain injury (sTBI) induced neuronal loss and brain atrophy contribute significantly to long-term disabilities. Brain extracellular matrix (ECM) associated chondroitin sulfate (CS) glycosaminoglycans promote neural stem cell (NSC) maintenance, and CS hydrogel implants have demonstrated the ability to enhance neuroprotection, in preclinical sTBI studies. However, the ability of neuritogenic chimeric peptide (CP) functionalized CS hydrogels in promoting functional recovery, after controlled cortical impact (CCI) and suction ablation (SA) induced sTBI, has not been previously demonstrated. We hypothesized that neuritogenic (CS)CP hydrogels will promote neuritogenesis of human NSCs, and accelerate brain tissue repair and functional recovery in sTBI rats.Approach.We synthesized chondroitin 4-Osulfate (CS-A)CP, and 4,6-O-sulfate (CS-E)CP hydrogels, using strain promoted azide-alkyne cycloaddition (SPAAC), to promote cell adhesion and neuritogenesis of human NSCs,in vitro; and assessed the ability of (CS-A)CP hydrogels in promoting tissue and functional repair, in a novel CCI-SA sTBI model,in vivo. Main results.Results indicated that (CS-E)CP hydrogels significantly enhanced human NSC aggregation and migration via focal adhesion kinase complexes, when compared to NSCs in (CS-A)CP hydrogels,in vitro. In contrast, NSCs encapsulated in (CS-A)CP hydrogels differentiated into neurons bearing longer neurites and showed greater spontaneous activity, when compared to those in (CS-E)CP hydrogels. The intracavitary implantation of (CS-A)CP hydrogels, acutely after CCI-SA-sTBI, prevented neuronal and axonal loss, as determined by immunohistochemical analyses. (CS-A)CP hydrogel implanted animals also demonstrated the significantly accelerated recovery of 'reach-to-grasp' function when compared to sTBI controls, over a period of 5-weeks.Significance.These findings demonstrate the neuritogenic and neuroprotective attributes of (CS)CP 'click' hydrogels, and open new avenues for the development of multifunctional glycomaterials that are functionalized with biorthogonal handles for sTBI repair.

Multimodal convergence in the pedunculopontine tegmental nucleus: Motor, sensory and theta-frequency inputs influence activity of single neurons.

The pedunculopontine tegmental nucleus of the brainstem (PPTg) has extensive interconnections and neuronal-behavioural correlates. It is implicated in movement control and sensorimotor integration. We investigated whether single neuron activity in freely moving rats is correlated with components of skilled forelimb movement, and whether individual neurons respond to both motor and sensory events. We found that individual PPTg neurons showed changes in firing rate at different times during the reach. This type of temporally specific modulation is like activity seen elsewhere in voluntary movement control circuits, such as the motor cortex, and suggests that PPTg neural activity is related to different specific events occurring during the reach. In particular, many neuronal modulations were time-locked to the end of the extension phase of the reach, when fine distal movements related to food grasping occur, indicating strong engagement of PPTg in this phase of skilled individual forelimb movements. In addition, some neurons showed brief periods of apparent oscillatory firing in the theta range at specific phases of the reach-to-grasp movement. When movement-related neurons were tested with tone stimuli, many also responded to this auditory input, allowing for sensorimotor integration at the cellular level. Together, these data extend the concept of the PPTg as an integrative structure in generation of complex movements, by showing that this function extends to the highly coordinated control of the forelimb during skilled reach to grasp movement, and that sensory and motor-related information converges on single neurons, allowing for direct integration at the cellular level.

The contribution of semantic distance knowledge to size constancy in perception and grasping when visual cues are limited.

To achieve a stable perception of object size in spite of variations in viewing distance, our visual system needs to combine retinal image information and distance cues. Previous research has shown that, not only retinal cues, but also extraretinal sensory signals can provide reliable information about depth and that different neural networks (perception versus action) can exhibit preferences in the use of these different sources of information during size-distance computations. Semantic knowledge of distance, a purely cognitive signal, can also provide distance information. Do the perception and action systems show differences in their ability to use this information in calculating object size and distance? To address this question, we presented 'glow-in-the-dark' objects of different physical sizes at different real distances in a completely dark room. Participants viewed the objects monocularly through a 1-mm pinhole. They either estimated the size and distance of the objects or attempted to grasp them. Semantic knowledge was manipulated by providing an auditory cue about the actual distance of the object: "20 cm", "30 cm", and "40 cm". We found that semantic knowledge of distance contributed to some extent to size constancy operations during perceptual estimation and grasping, but size constancy was never fully restored. Importantly, the contribution of knowledge about distance to size constancy was equivalent between perception and action. Overall, our study reveals similarities and differences between the perception and action systems in the use of semantic distance knowledge and suggests that this cognitive signal is useful but not a reliable depth cue for size constancy under restricted viewing conditions.

AutoRG: An automatized reach-to-grasp platform technology for assessing forelimb motor function, neural circuit activation, and cognition in rodents.

BACKGROUND: Rodent reach-to-grasp function assessment is a translationally powerful model for evaluating neurological function impairments and recovery responses. Existing assessment platforms are experimenter-dependent, costly, or low-throughput with limited output measures. Further, a direct histologic comparison of neural activation has never been conducted between any novel, automated platform and the well-established single pellet skilled reach task (SRT). NEW METHOD: To address these technological and knowledge gaps, we designed an open-source, low-cost Automatized Reach-to-Grasp (AutoRG) pull platform that reduces experimenter interventions and variability. We assessed reach-to-grasp function in rats across seven progressively difficult stages using AutoRG. We mapped AutoRG and SRT-activated motor circuitries in the rat brain using volumetric imaging of the immediate early gene-encoded Arc (activity-regulated cytoskeleton-associated) protein. RESULTS: Rats demonstrated robust forelimb reaching and pulling behavior after training in AutoRG. Reliable force versus time responses were recorded for individual reach events in real time, which were used to derive several secondary functional measures of performance. Moreover, we provide the first demonstration that for a training period of 30 min, AutoRG and SRT both engage similar neural responses in the caudal forelimb area (CFA), rostral forelimb area (RFA), and sensorimotor area (S1). CONCLUSION: AutoRG is the first low-cost, open-source pull system designed for the scale-up of volitional forelimb motor function testing and characterization of rodent reaching behavior. The similarities in neuronal activation patterns observed in the rat motor cortex after SRT and AutoRG assessments validate the AutoRG as a rigorously characterized, scalable alternative to the conventional SRT and expensive commercial systems.

Cortico-cortical drive in a coupled premotor-primary motor cortex dynamical system.

In the conventional view of sensorimotor control, the premotor cortex (PM) plans actions that are executed by the primary motor cortex (M1). This notion arises in part from many experiments that have imposed a preparatory "planning" period, during which PM becomes active without M1. But during many natural movements, PM and M1 are co-activated, making it difficult to distinguish their functional roles. We leverage coupled dynamical systems models (cDSMs) to uncover interactions between PM and M1 during movements performed with no preparatory period. We build cDSMs using neural and behavioral data recorded from two non-human primates as they performed a reach-grasp-manipulate task. PM and M1 interact dynamically throughout these movements. Whereas PM drives the M1 in some situations, in other situations, M1 drives PM activity, contrary to the conventional assumption. Our DSM framework provides additional predictions differentiating the roles of PM and M1 in controlling movement.

Reach-to-grasp kinematics and kinetics with and without visual feedback in early-stage Alzheimer's disease.

This study aimed to investigate the effects of early-stage Alzheimer's disease (AD) on the reach-to-grasp kinematics and kinetics with and without visual supervision of the grasping arm and hand. Seventeen patients who had been diagnosed with early-stage AD and 17 age- and gender-matched, cognitive normal (CN) adults participated in the experiment. A mirror operating system was designed to block the visual feedback of their grasping hand and forearms but to virtually show grasped targets. The target for reach-to-grasp kinematics was a reflective marker installed on a base; and the target for reach-to-grasp kinetics was a custom-made apparatus installed with two six-component force/torque transducers. Kinematics and kinetic parameters were used to quantify the reach-to-grasp performances. Results showed that the early-stage AD remarkably decreased the reaching speed, reduced the grasping accuracy and increased the transportation variability for reach-to-grasp kinematics. For kinetic analysis, early-stage AD extended the preload duration, disturbed the grip and lift forces coordination, and increased the feedforward proportion in the grasping force control. The AD-related changes in the reach-to-grasp kinematic and kinetic parameters depended on visual feedback and were associated with nervous system function according to correlation analyses with the neuropsychological testing. These results suggest that the abnormal kinematic and kinetic characteristics may correlate with the neuropsychological status of early-stage AD, and that the reach-to-grasp kinematic and kinetic maneuver could potentially be used as a novel tool for non-invasive screening or evaluation of early-stage AD.

Can we use peripheral vision to create a visuospatial map for compensatory reach-to-grasp reactions?

Perturbation-induced reach-to-grasp reactions are dependent on vision to capture environmental features of potential support surfaces. Previous research proposed the use of an intrinsic visuospatial map of the environment to reduce delays in motor responses (e.g., stepping, grasping a handrail). Forming such a map from foveal vision would be challenging during movement as it would require constant foveal scanning. The objective of this study was to determine if compensatory reach-to-grasp reactions could be successfully executed while relying on a visuospatial map acquired using peripheral vision. Subjects were instructed to respond to a perturbation by grasping a handle randomly located at 0°, 20° or 40° in their field of view under three visual conditions: full vision throughout the entire trial (FV), vision available prior to perturbation only (MAP), and vision available post-perturbation only (ONLINE). Electromyography was used to determine reaction time and kinematic data were collected to determine initial reach angle. Overall, participants were successful in arresting whole-body motion across all visual conditions and handle locations. Initial reach angles were target specific when vision was available prior to perturbation onset (FV and MAP). However, the 40° handle location produced a greater initial reach angle in MAP, suggesting some limitations for mapping in the further visual periphery. These findings suggest that peripheral vision contributes to the ability to spatially locate targets by building an a priori visuospatial map, which benefits the control of rapid compensatory reach-to-grasp reactions evoked in the response to unpredictable events of instability.

Global organization of neuronal activity only requires unstructured local connectivity.

Modern electrophysiological recordings simultaneously capture single-unit spiking activities of hundreds of neurons spread across large cortical distances. Yet, this parallel activity is often confined to relatively low-dimensional manifolds. This implies strong coordination also among neurons that are most likely not even connected. Here, we combine in vivo recordings with network models and theory to characterize the nature of mesoscopic coordination patterns in macaque motor cortex and to expose their origin: We find that heterogeneity in local connectivity supports network states with complex long-range cooperation between neurons that arises from multi-synaptic, short-range connections. Our theory explains the experimentally observed spatial organization of covariances in resting state recordings as well as the behaviorally related modulation of covariance patterns during a reach-to-grasp task. The ubiquity of heterogeneity in local cortical circuits suggests that the brain uses the described mechanism to flexibly adapt neuronal coordination to momentary demands.

Distributed and Localized Dynamics Emerge in the Mouse Neocortex during Reach-to-Grasp Behavior.

A long-standing question in systems neuroscience is to what extent task-relevant features of neocortical processing are localized or distributed. Coordinated activity across the neocortex has been recently shown to drive complex behavior in the mouse, while activity in selected areas is canonically associated with specific functions (e.g., movements in the case of the motor cortex). Reach-to-grasp (RtG) movements are known to be dependent on motor circuits of the neocortex; however, the global activity of the neocortex during these movements has been largely unexplored in the mouse. Here, we characterized, using wide-field calcium imaging, these neocortex-wide dynamics in mice of either sex engaging in an RtG task. We demonstrate that, beyond motor regions, several areas, such as the visual and the retrosplenial cortices, also increase their activity levels during successful RtGs, and homologous regions across the ipsilateral hemisphere are also involved. Functional connectivity among neocortical areas increases transiently around movement onset and decreases during movement. Despite this global phenomenon, neural activity levels correlate with kinematics measures of successful RtGs in sensorimotor areas only. Our findings establish that distributed and localized neocortical dynamics co-orchestrate efficient control of complex movements.SIGNIFICANCE STATEMENT Mammals rely on reaching and grasping movements for fine-scale interactions with the physical world. In the mouse, the motor cortex is critical for the execution of such behavior, yet little is known about the activity patterns across neocortical areas. Using the mesoscale-level networks as a model of cortical processing, we investigated the hypothesis that areas beyond the motor regions could participate in RtG planning and execution, and indeed a large network of areas is involved while performing RtGs. Movement kinematics correlates mostly with neural activity in sensorimotor areas. By demonstrating that distributed and localized neocortical dynamics for the execution of fine movements coexist in the mouse neocortex during RtG, we offer an unprecedented view on the neocortical correlates of mammalian motor control.

Plasticity in Cervical Motor Circuits following Spinal Cord Injury and Rehabilitation.

Neuroplasticity is a robust mechanism by which the central nervous system attempts to adapt to a structural or chemical disruption of functional connections between neurons. Mechanical damage from spinal cord injury potentiates via neuroinflammation and can cause aberrant changes in neural circuitry known as maladaptive plasticity. Together, these alterations greatly diminish function and quality of life. This review discusses contemporary efforts to harness neuroplasticity through rehabilitation and neuromodulation to restore function with a focus on motor recovery following cervical spinal cord injury. Background information on the general mechanisms of plasticity and long-term potentiation of the nervous system, most well studied in the learning and memory fields, will be reviewed. Spontaneous plasticity of the nervous system, both maladaptive and during natural recovery following spinal cord injury is outlined to provide a baseline from which rehabilitation builds. Previous research has focused on the impact of descending motor commands in driving spinal plasticity. However, this review focuses on the influence of physical therapy and primary afferent input and interneuron modulation in driving plasticity within the spinal cord. Finally, future directions into previously untargeted primary afferent populations are presented.

A wearable ring-shaped inertial system to identify action planning impairments during reach-to-grasp sequences: a pilot study.

BACKGROUND: The progressive ageing of the population is leading to an increasing number of people affected by cognitive decline, including disorders in executive functions (EFs), such as action planning. Current procedures to evaluate cognitive decline are based on neuropsychological tests, but novel methods and approaches start to be investigated. Reach-to-grasp (RG) protocols have shown that intentions can influence the EFs of action planning. In this work, we proposed a novel ring-shaped wearable inertial device, SensRing, to measure kinematic parameters during RG and after-grasp (AG) tasks with different end-goals. The aim is to evaluate whether SensRing can characterize the motor performances of people affected by Mild Neurocognitive Disorder (MND) with impairment in EFs. METHODS: Eight Individuals with dysexecutive MND, named d-MND, were compared to ten older healthy subjects (HC). They were asked to reach and grasp a can with three different intentions: to drink (DRINK), to place it on a target (PLACE), or to pass it to a partner (PASS). Twenty-one kinematic parameters were extracted from SensRing inertial data. RESULTS: Seven parameters resulted able to differentiate between HC and d-MND in the RG phase, and 8 features resulted significant in the AG phase. d-MND, indeed, had longer reaction times (in RG PLACE), slower peak velocities (in RG PLACE and PASS, in AG DRINK and PLACE), longer deceleration phases (in all RG and AG DRINK), and higher variability (in RG PLACE, in AG DRINK and PASS). Furthermore, d-MND showed no significant differences among conditions, suggesting that impairments in EFs influence their capabilities in modulating the action planning based on the end-goal. CONCLUSIONS: Based on this explorative study, the system might have the potential for objectifying the clinical assessment of people affected by d-MND by administering an easy motor test. Although these preliminary results have to be investigated in-depth in a larger sample, the portability, wearability, accuracy, and ease-of use of the system make the SensRing potentially appliable for remote applications at home, including analysis of protocols for neuromotor rehabilitation in patients affected by MND.

Reach-to-Grasp: A Multisensory Experience.

The reach-to-grasp movement is ordinarily performed in everyday living activities and it represents a key behavior that allows humans to interact with their environment. Remarkably, it serves as an experimental test case for probing the multisensory architecture of goal-oriented actions. This review focuses on experimental evidence that enhances or modifies how we might conceptualize the "multisensory" substrates of prehension. We will review evidence suggesting that how reach-to-grasp movements are planned and executed is influenced by information coming from different sensory modalities such as vision, proprioception, audition, taste, and olfaction. The review closes with some considerations about the predominant role of the multisensory constituents in shaping prehensile behavior and how this might be important for future research developments, especially in the rehabilitative domain.

Striatal bilateral control of skilled forelimb movement.

Skilled motor behavior requires bihemispheric coordination, and participation of striatal outputs originating from two neuronal groups identified by distinctive expression of D1 or D2 dopamine receptors. We trained mice to reach for and grasp a single food pellet and determined how the output pathways differently affected forelimb trajectory and task efficiency. We found that inhibition and excitation of D1-expressing spiny projection neurons (D1SPNs) have a similar effect on kinematics results, as if excitation and inhibition disrupt the whole ensemble dynamics and not exclusively one kind of output. In contrast, D2SPNs participate in control of target accuracy. Further, ex vivo electrophysiological comparison of naive mice and mice exposed to the task showed stronger striatal neuronal connectivity for ipsilateral D1 and contralateral D2 neurons in relation to the paw used. In summary, while the output pathways work together to smoothly execute skill movements, practice of the movement itself changes synaptic patterns.

Persistent grasping errors produce depth cue reweighting in perception.

When a grasped object is larger or smaller than expected, haptic feedback automatically recalibrates motor planning. Intriguingly, haptic feedback can also affect 3D shape perception through a process called depth cue reweighting. Although signatures of cue reweighting also appear in motor behavior, it is unclear whether this motor reweighting is the result of upstream perceptual reweighting, or a separate process. We propose that perceptual reweighting is directly related to motor control; in particular, that it is caused by persistent, systematic movement errors that cannot be resolved by motor recalibration alone. In Experiment 1, we inversely varied texture and stereo cues to create a set of depth-metamer objects: when texture specified a deep object, stereo specified a shallow object, and vice versa, such that all objects appeared equally deep. The stereo-texture pairings that produced this perceptual metamerism were determined for each participant in a matching task (Pre-test). Next, participants repeatedly grasped these depth metamers, receiving haptic feedback that was positively correlated with one cue and negatively correlated with the other, resulting in persistent movement errors. Finally, participants repeated the perceptual matching task (Post-test). In the condition where haptic feedback reinforced the texture cue, perceptual changes were correlated with changes in grasping performance across individuals, demonstrating a link between perceptual reweighting and improved motor control. Experiment 2 showed that cue reweighting does not occur when movement errors are rapidly corrected by standard motor adaptation. These findings suggest a mutual dependency between perception and action, with perception directly guiding action, and actions producing error signals that drive motor and perceptual learning.

Effects of high-frequency repetitive transcranial magnetic stimulation on reach-to-grasp performance in individuals with Parkinson's disease: a preliminary study.

Individuals with Parkinson's disease (PD) have deficits in reach-to-grasp (RTG) execution and visuospatial processing which may be a result of dopamine deficiency in two brain regions: primary motor cortex (M1) and dorsolateral prefrontal cortex (DLPFC). We hypothesized that improvement following M1 stimulation would be the result of a direct impact on motor execution; whereas, DLPFC stimulation would improve the role of DLPFC in visuospatial processing. The aim of pilot study was to investigate the effects of HF-rTMS on RTG performance by stimulating either M1 or DLPFC. Thirty individuals with PD participated (H&Y stages I-III). All of them were more affected on the right side. Participants were allocated into three groups. The DLPFC group received HF-rTMS over left DLPFC; while, the M1 group received HF-rTMS over left M1 of extensor digitorum communis representational area. The control group received HF-rTMS over the vertex. Before and immediately post HF-rTMS, right-hand RTG performance was measured under no barrier and barrier conditions. Additionally, TMS measures including motor-evoked-potential (MEP) amplitude and cortical silent period (CSP) were determined to verify the effects of HF-rTMS. For the results, there were no significant differences among the three groups. However, only the M1 group showed a significant decrease in movement time immediately after HF-rTMS for a barrier condition. Moreover, the M1 group showed a near-significant increase in hand opening and transport velocity. As for the DLPFC group, there was a near-significant increase in temporal transport-grasp coordination and a significant increase in velocity. Increased MEP amplitudes and a significantly longer CSP in the M1 and DLPFC groups confirmed the effects of HF-rTMS. Regarding non-significant results among the three groups, it is still inconclusive whether there were different effects of the rTMS on the two stimulation areas. This is a preliminary study demonstrating that HF-rTMS to M1 may improve RTG execution; whereas, HF-rTMS to DLPFC may improve visuospatial processing demands of RTG.

Agency and Performance of Reach-to-Grasp With Modified Control of a Virtual Hand: Implications for Rehabilitation.

This study investigated how modified control of a virtual hand executing reach-to-grasp affects functional performance and agency (perception of control). The objective of this work was to demonstrate positive relationships between reaching performance and grasping agency and motivate greater consideration of agency in movement rehabilitation. We hypothesized that agency and performance have positive correlation across varying control modes of the virtual hand. In this study, each participant controlled motion of a virtual hand through motion of his or her own hand. Control of the virtual hand was modified according to a specific control mode. Each mode involved the virtual hand moving at a modified speed, having noise, or including a level of automation. These specific modes represent potential control features to adapt for a rehabilitation device such as a prosthetic arm and hand. In this study, significant changes in agency and performance were observed across the control modes. Overall, a significant positive relationship (p < 0.001) was observed between the primary performance metric of reach (tracking a minimum path length trajectory) and an implicit measurement of agency (intentional binding). Intentional binding was assessed through participant perceptions of time-intervals between grasp contact and a sound event. Other notable findings include improved movement efficiency (increased smoothness, reduced acceleration) during expression of higher agency and shift toward greater implicit versus explicit agency with higher control speed. Positively relating performance and agency incentivizes control adaptation of powered movement devices, such as prostheses or exoskeletons, to maximize both user engagement and functional performance. Agency-based approaches may foster user-device integration at a cognitive level and facilitate greater clinical retention of the device. Future work should identify robust and automated methods to adapt device control for increased agency. Objectives include how virtual reality (VR) may identify optimal control of real-world devices and assessing real-time agency from neurophysiological signals.

Toward natural grasping with a tool: effects of practice and required accuracy on the kinematics of tool-use grasping.

Studies have suggested that the proficiency of an end effector is the primary factor that defines kinematics of reach-to-grasp movements across the types of effectors, such as the hand or a tool. In particular, the duration of the plateau, or the time of static open aperture (i.e., the distance between tips of effectors), is typically longer for tool use compared with natural grasping with a hand. This study investigated how improvement in the proficiency of tool use modifies the kinematics of reach-to-grasp movements. To clarify the effects of required accuracy on the kinematics in tool-use grasping, movement speed and difficulty of grasping were manipulated. The results showed that plateau duration, the length of which indicates that reaching and grasping components are temporally dissociated, shortened as tool-use practice proceeded. These results indirectly support the idea that shortened plateau duration was induced by improvement in the proficiency of tool use. Moreover, plateau duration was shortened at faster movement speeds or under conditions not requiring accurate grasping, even without any practice of tool-use grasping. Additional analyses found that plateau duration did not scale with movement time. These results suggest that the kinematic features supposed to be characteristic of tool-use grasping are not inevitable but are greatly influenced by a strategy that is not intentionally but rather automatically implemented to compensate for the lack of proficiency of end effectors, in agreement with the idea that the brain focuses on the tips of an end effector regardless of its effector type in reach-to-grasp movements.NEW & NOTEWORTHY This study is the first reporting the relation between characteristic aperture time profile, called plateau duration, and movement time of tool-use grasping. The results suggest that improved coordination between reaching and grasping components was induced by improvement in the proficiency of tool use but not by just shortened movement time. The results also indicate the possibility that the constraints for calculations in motor planning are essentially the same between hand-use grasping and tool-use grasping.