Healthy adults favor stable left/right hand choices over performance at an unconstrained reach-to-grasp task.

Reach-to-grasp actions are fundamental to the daily activities of human life, but few methods exist to assess individuals' reaching and grasping actions in unconstrained environments. The Block Building Task (BBT) provides an opportunity to directly observe and quantify these actions, including left/right hand choices. Here we sought to investigate the motor and non-motor causes of left/right hand choices, and optimize the design of the BBT, by manipulating motor and non-motor difficulty in the BBT's unconstrained reach-to-grasp task. We hypothesized that greater motor and non-motor (e.g. cognitive/perceptual) difficulty would drive increased usage of the dominant hand. To test this hypothesis, we modulated block size (large vs. small) to influence motor difficulty, and model complexity (10 vs. 5 blocks per model) to influence non-motor difficulty, in healthy adults (n = 57). Our data revealed that increased motor and non-motor difficulty led to lower task performance (slower task speed), but participants only increased use of their dominant hand only under the most difficult combination of conditions: in other words, participants allowed their performance to degrade before changing hand choices, even though participants were instructed only to optimize performance. These results demonstrate that hand choices during reach-to grasp actions are more stable than motor performance in healthy right-handed adults, but tasks with multifaceted difficulties can drive individuals to rely more on their dominant hand.

Roles of Handedness and Hemispheric Lateralization: Implications for Rehabilitation of the Central and Peripheral Nervous Systems: A Rapid Review.

IMPORTANCE: Handedness and motor asymmetry are important features of occupational performance. With an increased understanding of the basic neural mechanisms surrounding handedness, clinicians will be better able to implement targeted, evidence-based neurorehabilitation interventions to promote functional independence. OBJECTIVE: To review the basic neural mechanisms behind handedness and their implications for central and peripheral nervous system injury. DATA SOURCES: Relevant published literature obtained via MEDLINE. FINDINGS: Handedness, along with performance asymmetries observed between the dominant and nondominant hands, may be due to hemispheric specializations for motor control. These specializations contribute to predictable motor control deficits that are dependent on which hemisphere or limb has been affected. Clinical practice recommendations for occupational therapists and other rehabilitation specialists are presented. CONCLUSIONS AND RELEVANCE: It is vital that occupational therapists and other rehabilitation specialists consider handedness and hemispheric lateralization during evaluation and treatment. With an increased understanding of the basic neural mechanisms surrounding handedness, clinicians will be better able to implement targeted, evidence-based neurorehabilitation interventions to promote functional independence. Plain-Language Summary: The goal of this narrative review is to increase clinicians' understanding of the basic neural mechanisms related to handedness (the tendency to select one hand over the other for specific tasks) and their implications for central and peripheral nervous system injury and rehabilitation. An enhanced understanding of these mechanisms may allow clinicians to better tailor neurorehabilitation interventions to address motor deficits and promote functional independence.

Patient Outcomes After Peripheral Nerve Injury Depend on Bimanual Dexterity and Preserved Use of the Affected Hand.

BACKGROUND: Little is known about how peripheral nerve injury affects human performance, behavior, and life. Hand use choices are important for rehabilitation after unilateral impairment, but rarely measured, and are not changed by the normal course of rehabilitation and daily life. OBJECTIVE: To identify the relationship between hand use (L/R choices), motor performance, and patient-centered outcomes. METHODS: Participants (n = 48) with unilateral peripheral nerve injury were assessed for hand use via Block Building Task, Motor Activity Log, and Edinburgh Handedness Inventory; dexterity (separately for each hand) via Nine-Hole Peg Test, Jebsen Taylor Hand Function Test, and a precision drawing task; patient-centered outcomes via surveys of disability, activity participation, and health-related quality of life; and injury-related factors including injury cause and affected nerve. Factor Analysis of Mixed Data was used to explore relationships between these variables. The data were analyzed under 2 approaches: comparing dominant hand (DH) versus non-dominant hand (NH), or affected versus unaffected hand. RESULTS: The data were best explained by 5 dimensions. Good patient outcomes were associated with NH performance, DH performance (separately and secondarily to NH performance), and preserved function and use of the affected hand; whereas poor patient outcomes were associated with preserved but unused function of the affected hand. CONCLUSION: After unilateral peripheral nerve injury, hand function, hand usage, and patient life arise from a complex interaction of many factors. To optimize rehabilitation after unilateral impairment, new rehabilitation methods are needed to promote performance and use with the NH, as well as the injured hand.

Healthy adults favor stable left/right hand choices over performance at an unconstrained reach-to-grasp task.

Reach-to-grasp actions are fundamental to the daily activities of human life, but few methods exist to assess individuals' reaching and grasping actions in unconstrained environments. The Block Building Task (BBT) provides an opportunity to directly observe and quantify these actions, including left/right hand choices. Here we sought to investigate the motor and non-motor causes of left/right hand choices, and optimize the design of the BBT, by manipulating motor and non-motor difficulty in the BBT's unconstrained reach-to-grasp task We hypothesized that greater motor and non-motor (e.g. cognitive/perceptual) difficulty would drive increased usage of the dominant hand. To test this hypothesis, we modulated block size (large vs. small) to influence motor difficulty, and model complexity (10 vs. 5 blocks per model) to influence non-motor difficulty, in healthy adults (n=57). We hypothesized that healthy adults with high non-dominant hand performance in a precision drawing task should be more likely to use their non-dominant hand in the BBT. Our data revealed that increased motor and non-motor difficulty led to lower task performance (slower speed), but participants only increased use of their dominant hand only under the most difficult combination of conditions: in other words, participants allowed their performance to degrade before changing hand choices, even though participants were instructed only to optimize performance. These results demonstrate that hand choices during reach-to grasp actions are more stable than motor performance in healthy right-handed adults, but tasks with multifaceted difficulties can drive individuals to rely more on their dominant hand. Statements and Declarations: Dr. Philip and Washington University in St. Louis have a licensing agreement with PlatformSTL to commercialize the iPad app used in this study.

Quantifying differences in fMRI preprocessing pipelines via OGRE (One-step General Registration and Extraction).

Volumetric preprocessing methods continue to enjoy great popularity in the analysis of functional MRI (fMRI) data. Among these methods, the software packages FSL (FMRIB, Oxford, UK) and FreeSurfer (LCN, Charlestown, MA) are omnipresent throughout the field. However, it remains unknown what advantages an integrated FSL+FreeSurfer preprocessing approach might provide over FSL alone. Here we developed the One-step General Registration and Extraction (OGRE) pipeline to combine FreeSurfer and FSL tools for brain extraction and registration, for FSL volumetric analysis of fMRI data. We compared preprocessing approaches in a dataset wherein adult human volunteers (N=26) performed a precision drawing task during fMRI scanning. OGRE's preprocessing, compared to traditional FSL preprocessing, led to lower inter-individual variability across the brain, more precise brain extraction, and greater detected activation in sensorimotor areas contralateral to movement. This demonstrates that the introduction of FreeSurfer tools via OGRE preprocessing can improve fMRI data analysis, in the context of FSL's volumetric analysis approach. The OGRE pipeline provides a turnkey method to integrate FreeSurfer-based brain extraction and registration with FSL analysis of task fMRI data.

Motor Assessment With the STEGA iPad App to Measure Handwriting in Children.

IMPORTANCE: Handwriting and the fine motor control (hand and fingers) underlying it are key indicators of numerous motor disorders, especially among children. However, current assessment methods are expensive, slow, and subjective, leading to a lack of knowledge about the relationship between handwriting and motor control. OBJECTIVE: To develop and validate the iPad precision drawing app Standardized Tracing Evaluation and Grapheme Assessment (STEGA) to enable rapid quantitative assessment of fine motor control and handwriting. DESIGN: Cross-sectional, single-arm observational study. SETTING: Academic research institution. PARTICIPANTS: Fifty-seven typically developing right-handed children ages 9 to 12 yr with knowledge of cursive. OUTCOMES AND MEASURES: Predicted quality, measured as the correlation between handwriting letter legibility (Evaluation Tool of Children's Handwriting-Cursive [ETCH-C]) and predicted legibility (calculated from STEGA's 120 Hz, nine-variable data). RESULTS: STEGA successfully predicted handwriting (r2 = .437, p < .001) using a support vector regression method. Angular error was the most important aspect of STEGA performance. STEGA was much faster to administer than the ETCH-C (M = 6.7 min, SD = 1.3, versus M = 19.7 min, SD = 5.2). CONCLUSIONS AND RELEVANCE: Assessment of motor control (and especially pen direction control) may provide a meaningful, objective way to assess handwriting. Future studies are needed to validate STEGA with a wider age range, but the initial results indicate that STEGA can provide the first rapid, quantitative, high-resolution, telehealth-capable assessment of the motor control that underpins handwriting. What This Article Adds: The ability to control pen direction may be the most important motor skill for successful handwriting. STEGA may provide the first criterion standard for the fine motor control skills that underpin handwriting, suitable for rehabilitation research and practice.

Corrigendum: Changes in primary somatosensory cortex following allogeneic hand transplantation or autogenic hand replantation.

[This corrects the article DOI: 10.3389/fnimg.2022.919694.].

Failure to Compensate: Patients With Nerve Injury Use Their Injured Dominant Hand, Even When Their Nondominant Is More Dexterous.

OBJECTIVE: To identify how individuals respond to unilateral upper extremity peripheral nerve injury via compensation (increased use of the nondominant hand). We hypothesized that injury to the dominant hand would have a greater effect on hand use (left vs right choices). We also hypothesized that compensation would not depend on current (postinjury) nondominant hand performance because many patients undergo rehabilitation that is not designed to alter hand use. DESIGN: Observational survey, single-arm. SETTINGS: Academic research institution and referral center. PARTICIPANTS: A total of 48 adults (N=48) with unilateral upper extremity peripheral nerve injury. Another 14 declined participation. Referred sample, including all eligible patients from 16 months at 1 nerve injury clinic and 1 hand therapy clinic. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Hand use (% of actions with each hand) via Block Building Task. Dexterity via Jebsen-Taylor Hand Function. RESULTS: Participants preferred their dominant hand regardless of whether it was injured: hand usage (dominant/nondominant) did not differ from typical adults, regardless of injured side (P>.07), even though most participants (77%) were more dexterous with their uninjured nondominant hand (mean asymmetry index, -0.16±0.25). The Block Building Task was sensitive to hand dominance (P=2 × 10-4) and moderately correlated with Motor Activity Log amount scores (r2=0.33, P<.0001). Compensation was associated only with dominant hand dexterity (P=3.9 × 10-3), not on nondominant hand dexterity, rehabilitation, or other patient and/or injury factors (P>.1). CONCLUSIONS: Patients with peripheral nerve injury with dominant hand injury do not compensate with their unaffected nondominant hand, even if it is more dexterous. For the subset of patients unlikely to recover function with the injured hand, they could benefit from rehabilitation that encourages compensation with the nondominant hand.

Quality of Life and Psychosocial Factors as Predictors of Pain Relief Following Nerve Surgery.

Background: Peripheral nerve injuries may result in pain, disability, and decreased quality of life (QoL). Pain is an incompletely understood experience and is associated with emotional and behavioral qualities. We hypothesized that pain following peripheral nerve surgery could be predicted by changes in emotions or QoL postoperatively. Methods: Using prospectively collected data, a retrospective study design was used to evaluate the relationships among pain, QoL, and psychosocial factors in patients who underwent peripheral nerve surgery. Patients completed questionnaires rating pain; impact of pain on QoL, sadness, depression, frustration, anger, and hopefulness before surgery; and each postoperative follow-up visit. Multilevel modeling was used to assess the concurrent and lagged relationships between pain and psychosocial factors. Results: Increased pain was concurrently associated with decreased hopefulness (P = .001) and increased the impact on QoL, sadness, depression, and anger (P < .001). In lagged analyses, the impact on QoL and anger prospectively predicted pain (P < .001 and P = .02, respectively). Pain predicted subsequent scores of QoL, sadness, depression, anger, and hopefulness (P < .01). Having an upper limb nerve injury and self-report of "no comment for childhood trauma" were predictors of postsurgical pain. Conclusion: Psychosocial measures and pain are reciprocally related among patients who underwent surgery for peripheral nerve injuries or compression. Our study provides evidence of the important relationships among psychosocial factors, pain, and outcome and identifies treatment targets following nerve surgery.

Interhemispheric Parietal-Frontal Connectivity Predicts the Ability to Acquire a Nondominant Hand Skill.

Introduction: After chronic impairment of the right dominant hand, some individuals are able to compensate with increased performance with the intact left nondominant hand. This process may depend on the nondominant (right) hemisphere's ability to access dominant (left) hemisphere mechanisms. To predict or modulate patients' ability to compensate with the left hand, we must understand the neural mechanisms and connections that underpin this process. Methods: We studied 17 right-handed healthy adults who underwent resting-state functional connectivity (FC) magnetic resonance imaging scans before 10 days of training on a left-hand precision drawing task. We sought to identify right-hemisphere areas where FC from left-hemisphere seeds (primary motor cortex, intraparietal sulcus [IPS], inferior parietal lobule) would predict left-hand skill learning or magnitude. Results: Left-hand skill learning was predicted by convergent FC from left primary motor cortex and left IPS onto the same small region (0.31 cm3) in the right superior parietal lobule (SPL). Discussion: For patients who must compensate with the left hand, the right SPL may play a key role in integrating left-hemisphere mechanisms that typically control the right hand. Our study provides the first model of how interhemispheric functional connections in the human brain may support compensation after chronic injury to the right hand.

Cortical Plasticity in Rehabilitation for Upper Extremity Peripheral Nerve Injury: A Scoping Review.

IMPORTANCE: Poor outcomes after upper extremity peripheral nerve injury (PNI) may arise, in part, from the challenges and complexities of cortical plasticity. Occupational therapy practitioners need to understand how the brain changes after peripheral injury and how principles of cortical plasticity can be applied to improve rehabilitation for clients with PNI. OBJECTIVE: To identify the mechanisms of cortical plasticity after PNI and describe how cortical plasticity can contribute to rehabilitation. DATA SOURCES: PubMed and Embase (1900-2017) were searched for articles that addressed either (1) the relationship between PNI and cortical plasticity or (2) rehabilitative interventions based on cortical plastic changes after PNI. STUDY SELECTION AND DATA COLLECTIO: : PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines were followed. Articles were selected if they addressed all of the following concepts: human PNI, cortical plasticity, and rehabilitation. Phantom limb pain and sensation were excluded. FINDINGS: Sixty-three articles met the study criteria. The most common evidence level was Level V (46%). We identified four commonly studied mechanisms of cortical plasticity after PNI and the functional implications for each. We found seven rehabilitative interventions based on cortical plasticity: traditional sensory reeducation, activity-based sensory reeducation, selective deafferentation, cross-modal sensory substitution, mirror therapy, mental motor imagery, and action observation with simultaneous peripheral nerve stimulation. CONCLUSION AND RELEVANCE: The seven interventions ranged from theoretically well justified (traditional and activity-based sensory reeducation) to unjustified (selective deafferentation). Overall, articles were heterogeneous and of low quality, and future research should prioritize randomized controlled trials for specific neuropathies, interventions, or cortical plasticity mechanisms. WHAT THIS ARTICLE ADDS: This article reviews current knowledge about how the brain changes after PNI and how occupational therapy practitioners can take advantage of those changes for rehabilitation.

Impact of Handedness on Disability After Unilateral Upper-Extremity Peripheral Nerve Disorder.

Background: Impairment of the dominant hand should lead to greater disability than impairment of the nondominant hand, but few studies have tested this directly, especially in the domain of upper-extremity peripheral nerve disorder. The aim of this study was to identify the association between hand dominance and standardized measures of disability and health status after upper-extremity peripheral nerve disorder. Methods: An existing database was reanalyzed to identify the relationship between affected-side (dominant vs nondominant) on individuals with unilateral upper-extremity peripheral nerve disorder (N = 400). Primary measure of disability was the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire. Results: We found no differences in standardized measures of disability or health status between patients with affected dominant hand and patients with an affected nondominant hand. However, a post hoc exploratory analysis revealed that patients with an affected dominant hand reported substantially reduced ability to perform 2 activities in the DASH questionnaire: "write" and "turn a key." Conclusions: Following unilateral upper-extremity peripheral nerve disorder, impairment of the dominant hand (compared with impairment of the nondominant hand) is associated with reduced ability to perform specific activities, but this reduced ability is not reflected in standardized measures of disability and health status. To adequately identify disability following unilateral impairment of the dominant hand with the DASH, individual items must be used instead of the total score. New or alternative measures are also recommended.

Interhemispheric transfer of post-amputation cortical plasticity within the human somatosensory cortex.

Animal models reveal that deafferenting forelimb injuries precipitate reorganization in both contralateral and ipsilateral somatosensory cortices. The functional significance and duration of these effects are unknown, and it is unclear whether they also occur in injured humans. We delivered cutaneous stimulation during functional magnetic resonance imaging (fMRI) to map the sensory cortical representation of the intact hand and lower face in a group of chronic, unilateral, upper extremity amputees (N = 19) and healthy matched controls (N = 29). Amputees exhibited greater activity than controls within the deafferented former sensory hand territory (S1f) during stimulation of the intact hand, but not of the lower face. Despite this cortical reorganization, amputees did not differ from controls in tactile acuity on their intact hands. S1f responses during hand stimulation were unrelated to tactile acuity, pain, prosthesis usage, or time since amputation. These effects appeared specific to the deafferented somatosensory modality, as fMRI visual mapping paradigm failed to detect any differences between groups. We conclude that S1f becomes responsive to cutaneous stimulation of the intact hand of amputees, and that this modality-specific reorganizational change persists for many years, if not indefinitely. The functional relevance of these changes, if any, remains unknown.

Grasping with a new hand: Improved performance and normalized grasp-selective brain responses despite persistent functional changes in primary motor cortex and low-level sensory and motor impairments.

Hand loss can now be reversed through surgical transplantation years or decades after amputation. Remarkably, these patients come to use their new hand to skilfully grasp and manipulate objects. The brain mechanisms that make this possible are unknown. Here we test the hypothesis that the anterior intraparietal cortex (aIPC) - a multimodal region implicated in hand preshaping and error correction during grasping - plays a key role in this compensatory grasp control. Motion capture and fMRI are used to characterize hand kinematics and brain responses during visually guided grasping with a transplanted hand at 26 and 41 months post-transplant in patient DR, a former hand amputee of 13 years. Compared with matched controls, DR shows increasingly normal grasp kinematics paralleled by increasingly robust grasp-selective fMRI responses within the very same brain areas that show grasp-selectivity in controls, including the aIPC, premotor and cerebellar cortices. Paradoxically, over this same time DR exhibits significant limitations in basic sensory and motor functions, and persistent amputation-related functional reorganization of primary motor cortex. Movements of the non-transplanted hand positively activate the ipsilateral primary motor hand area - a functional marker of persistent interhemispheric amputation-related reorganization. Our data demonstrate for the first time that even after more than a decade of living as an amputee the normative functional brain organization governing the control of grasping can be restored. We propose that the aIPC and interconnected premotor and cerebellar cortices enable grasp normalization by compensating for the functional impact of reorganizational changes in primary sensorimotor cortex and targeting errors in regenerating peripheral nerves.

Contributions of the parietal cortex to increased efficiency of planning-based action selection.

Response selection is foundational to adaptive behavior, and considerable attention has been devoted to investigating this behavior under conditions in which the mapping between stimuli and responses is fixed. Results from prior studies implicate the left supramarginal gyrus (SMg), premotor and prefrontal cortices, as well as the cerebellum in this essential function. Yet, many goal-directed motor behaviors have multiple solutions with flexible mappings between stimuli and responses whose solutions are believed to involve prospective planning. Studies of selection under conditions of flexible mappings also reveal involvement of the left SMg, as well as bilateral premotor, superior parietal cortex (SPL) and pre-supplementary motor (pre-SMA) cortices, along with the cerebellum. This evidence is, however, limited by exclusive reliance on tasks that involve selection in the absence of overt action execution and without complete control of possible confounding effects related to differences in stimulus and response processing demands. Here, we address this limitation through use of a novel fMRI repetition suppression (FMRI-RS) paradigm. In our prime-probe design, participants select and overtly pantomime manual object rotation actions when the relationship between stimuli and responses is either flexible (experimental condition) or fixed (control condition). When trials were repeated in prime-probe pairs of the experimental condition, we detected improvements in performance accompanied by a significant suppression of blood oxygen-level dependent (BOLD) responses in: left SMg extending into and along the length of the intraparietal sulcus (IPS), right IPS, bilateral caudal superior parietal lobule (cSPL), dorsal premotor cortex (dPMC), pre-SMA, and in the lateral cerebellum. Further, region-of-interest analyses revealed interaction effects of fMRI-RS in the experimental versus control condition within left SMg and cerebellum, as well as in bilateral caudal SPL. These efficiency effects cannot be attributed to the repetition of stimulus or response processing, but instead are planning-specific and generally consistent with earlier findings from conventional fMRI investigations. We conclude that repetition-related increases in the efficiency of planning-based selection appears to be associated with parieto-cerebellar networks.

Increased functional connectivity between cortical hand areas and praxis network associated with training-related improvements in non-dominant hand precision drawing.

Chronic forced use of the non-dominant left hand yields substantial improvements in the precision and quality of writing and drawing. These changes may arise from increased access by the non-dominant (right) hemisphere to dominant (left) hemisphere mechanisms specialized for end-point precision control. To evaluate this prediction, 22 healthy right-handed adults underwent resting state functional connectivity (FC) MRI scans before and after 10 days of training on a left hand precision drawing task. 89% of participants significantly improved left hand speed, accuracy, and smoothness. Smoothness gains were specific to the trained left hand and persistent: 6 months after training, 71% of participants exhibited above-baseline movement smoothness. Contrary to expectations, we found no evidence of increased FC between right and left hemisphere hand areas. Instead, training-related improvements in left hand movement smoothness were associated with increased FC between both sensorimotor hand areas and a left-lateralized parieto-prefrontal network implicated in manual praxis. By contrast, skill retention at 6 months was predicted by changes including decreased FC between the representation of the trained left hand and bilateral sensorimotor, parietal, and premotor cortices, possibly reflecting consolidation and a disengagement of early learning processes. These data indicate that modest amounts of training (<200min total) can induce substantial, persistent improvements the precision and quality of non-dominant hand control in healthy adults, supported by strengthened connectivity between bilateral sensorimotor hand areas and a left-lateralized parieto-prefrontal praxis network.

Compensatory changes accompanying chronic forced use of the nondominant hand by unilateral amputees.

Amputation of the dominant hand forces patients to use the nondominant hand exclusively, including for tasks (e.g., writing and drawing) that were formerly the sole domain of the dominant hand. The behavioral and neurological effects of this chronic forced use of the nondominant hand remain largely unknown. Yet, these effects may shed light on the potential to compensate for degradation or loss of dominant hand function, as well as the mechanisms that support motor learning under conditions of very long-term training. We used a novel precision drawing task and fMRI to investigate 8 adult human amputees with chronic (mean 33 years) unilateral dominant (right) hand absence, and right-handed matched controls (8 for fMRI, 19 for behavior). Amputees' precision drawing performances with their left hands reached levels of smoothness (associated with left hemisphere control), acceleration time (associated with right hemisphere control), and speed equivalent to controls' right hands, whereas accuracy maintained a level comparable with controls' left hands. This compensation is supported by an experience-dependent shift from heavy reliance on the dorsodorsal parietofrontal pathway (feedback control) to the ventrodorsal pathway and prefrontal regions involved in the cognitive control of goal-directed actions. Relative to controls, amputees also showed increased activity within the former cortical sensorimotor hand territory in the left (ipsilateral) hemisphere. These data demonstrate that, with chronic and exclusive forced use, the speed and quality of nondominant hand precision endpoint control in drawing can achieve levels nearly comparable with the dominant hand.

Simultaneous reconstruction of continuous hand movements from primary motor and posterior parietal cortex.

Primary motor cortex (MI) and parietal area PE both participate in cortical control of reaching actions, but few studies have been able to directly compare the form of kinematic encoding in the two areas simultaneously during hand tracking movements. To directly compare kinematic coding properties in these two areas under identical behavioral conditions, we recorded simultaneously from two chronically implanted multielectrode arrays in areas MI and PE (or areas 2/5) during performance of a continuous manual tracking task. Monkeys manually pursued a continuously moving target that followed a series of straight-line movement segments, arranged in a sequence where the direction (but not length) of the upcoming segment varied unpredictably as each new segment appeared. Based on recordings from populations of MI (31-143 units) and PE (22-87 units), we compared hand position and velocity reconstructions based on linear filters. We successfully reconstructed hand position and velocity from area PE (mean r (2) = 0.751 for position reconstruction, r (2) = 0.614 for velocity), demonstrating trajectory reconstruction from each area. Combing these populations provided no reconstruction improvements, suggesting that kinematic representations in MI and PE encode overlapping hand movement information, rather than complementary or unique representations. These overlapping representations may reflect the areas' common engagement in a sensorimotor feedback loop for error signals and movement goals, as required by a task with continuous, time-evolving demands and feedback. The similarity of information in both areas suggests that either area might provide a suitable target to obtain control signals for brain computer interface applications.

Stimulus-response correspondence across peripersonal space is unaffected by chronic unilateral limb loss.

Previous findings show an advantage in response speed when stimulus and response correspond spatially (i.e., the Simon effect). Chronic unilateral amputees show altered spatial perception near their affected hand, providing an opportunity to investigate whether experience also affects the visuomotor stimulus-response (S-R) mapping that underlies the Simon effect. We used a two-alternative, forced-choice paradigm to probe the spatial correspondence between visual cues and responses, in 14 unilateral upper limb amputees and 14 matched controls. We presented visual stimuli in 5 different locations within peripersonal space, including the midline, and found a smooth gradient of S-R correspondence effects. This is consistent with the hypothesis that S-R correspondence is represented along a spatial gradient. Unilateral amputees performed indistinguishably from matched controls, regardless of whether stimuli appeared in the hemispace ipsi- or contralateral to their missing limbs. This is inconsistent with the hypothesis that experience-dependent visual distortions entail changes in the S-R mapping; alternatively, it could reflect a complete experience independence of the Simon effect. We propose that the affordance competition hypothesis (Cisek in Philos Trans R Soc B Biol Sci 362:1585-1599, 2007) explains the Simon effect and the underlying gradient of S-R correspondence.