Experimental Brain Research

Cybersickness is a major barrier to the widespread adoption of virtual reality (VR), yet its underlying neurophysiological mechanisms remain poorly understood. This study investigated the relationship between vestibulomotor weighting and cybersickness. Vestibulomotor weighting was quantified using electrical vestibular stimulation (EVS), with coherence and gain between the EVS input and medial-lateral center-of-pressure (ML-CoP) responses indexing the contribution of vestibular input to postural control. Thirty-eight healthy young adults (females n=21, males n=17) completed a standing VR rollercoaster task while receiving continuous stochastic EVS (0-25 Hz; {+/-}4.5 mA), with ML-CoP responses recorded using a force plate. Cybersickness was assessed using the Fast Motion Sickness Scale (FMS) and Simulator Sickness Questionnaire, and participants were classified as non-sick (FMS < 5), medium-sick (FMS [&ge;] 5), or high-sick (terminated the VR exposure early due to intolerance). Baseline EVS-ML-CoP coherence across 2.5-8 Hz was significantly greater in high-sick than in non-sick participants, indicating elevated vestibulomotor weighting in individuals who developed symptoms. During VR exposure, coherence declined over time in symptomatic groups (mean slope = -0.0027 for medium-sick), whereas non-sick participants maintained consistently low coherence (mean slope = -0.0005). Despite this reduction in vestibular coupling, postural sway increased in the high-sick group relative to the medium-and non-sick groups (+29% vs. -7% and -30% change in ML-CoP RMS, respectively), while vestibular-evoked response amplitude decreased (gain reduced by 64% across 2.5-3.5 Hz). These findings indicate that greater baseline vestibulomotor weighting was associated with increased susceptibility to cybersickness, whereas reductions in vestibular contributions during VR with EVS reflected adaptive reweighting that was insufficient to prevent instability and symptom progression. Together, the results highlight baseline sensory reliance as a key determinant of cybersickness vulnerability and suggest that reweighting during exposure plays a secondary, mitigating role. New and NoteworthyWe provide the first evidence that baseline vestibulomotor weighting predicts susceptibility to cybersickness in virtual reality and is dynamically reduced during exposure. Using electrical vestibular stimulation, we show that symptomatic individuals begin with greater reliance on vestibular input for postural control and progressively downweight these signals in response to sensory conflict.

A consistent finding across studies with older adults is that they typically perform worse at spatial memory tasks, particularly those conducted in virtual reality and involving novel environments, compared to young adults. While the underlying reasons for this difference remain unclear, some proposed hypotheses include differences in sensory cue integration and cue conflict resolution. Here, we tested older (n = 29) and young adults (n = 28) in immersive and walkable virtual reality using both correctly rendered and illusory hallways to test how visual cues (i.e., an intersection) and self-motion cues are integrated. In the illusory or false-intersection condition, we hypothesized that participants who walked an uncrossed path would merge two disconnected intersections, creating the illusion of a crossed path. The overall accuracy and pointing patterns were similar between young and older adults in both true- and false-intersection conditions. We did find, however, a significant age by condition interaction effect in egocentric pointing variability where older adults showed lower variability in the illusory condition and higher variability in the control condition. At the same time, older adults also drew worse maps for the control condition compared to young adults. However, the pointing error correlated with the accuracy of maps drawn regardless of age, suggesting that the pointing patterns shown by both age groups related to their underlying representations of the paths. Our findings are inconsistent with a global deficit in allocentric navigation or path integration and instead suggest that more subtle differences in strategy use might manifest with age.

IntroductionAction observation modulates corticospinal excitability, with most previous studies indicating an increase in excitability in the muscles involved in the observed movement. In addition, previous work suggests that modulation of corticospinal excitability could be specific to the timing of the stimulation, muscle, and direction of movement. Here we examined the influence of these factors on corticospinal excitability. MethodParticipants observed stimuli presenting a static hand, followed by an image of the endpoint of an index/little finger abduction movement. Transcranial magnetic stimulation was delivered at time points from 100-800ms after movement onset. Stimuli were presented in various orientations to study possible effects of anatomical positioning and movement direction, compared relative to the control condition of a static hand. ResultsCorticospinal excitability was lower at early timings (100-400ms), before rising to a plateau at later timings (500-800ms) which did not differ from the static hand condition. This facilitation was muscle-specific, with higher excitability for the muscle involved in the observed movement. By contrast, the relative direction of movement did not influence corticospinal excitability. DiscussionThese results replicate the time-dependent modulation of corticospinal excitability induced by action observation; however, we argue that simply interpreting such effects as an increase in excitability may be overly simplistic. In line with previous studies, we argue that the choice of control condition used during action observation studies may be critical to the overall direction of effects.

Motor imagery is a cognitive process that engages the motor system and facilitates motor learning, recovery, and performance. Its effectiveness relies on the activation of corticospinal pathways, which can be modulated by action observation. This study investigated whether observing graspable objects facilitates corticospinal excitability during motor imagery, and whether immersive virtual reality amplifies this effect. Twelve healthy adults of either sex completed a single session involving six conditions: rest, object observation on a screen or in virtual reality, motor imagery alone, and combined observation with motor imagery. Transcranial magnetic stimulation was used to record motor-evoked potentials from hand and forearm muscles, and fatigue and imagery quality were quantified. Results showed that observing a manipulable object during motor imagery significantly increased corticospinal excitability. This facilitation was strongest when the object was presented in a virtual environment. The effect was muscle-specific, targeting the agonist hand muscle of the imagined action (Abductor Pollicis Brevis), and was more pronounced at the higher stimulation intensity. Fatigue and imagery quality were similar across conditions. These findings indicate that object affordances can prime motor circuits and enhance motor imagery-induced neural activation, with immersive environments further reinforcing this effect. This is the first study demonstrating that combining motor imagery with virtual object observation maximizes corticospinal excitability. This approach may represent a promising tool for rehabilitation and sports training. Further studies should identify the optimal parameters and the neurophysiological markers of cortical modulation for this combination. NEW & NOTEWORTHYUsing transcranial magnetic stimulation with immersive virtual reality, we showed for the first time that observing a virtual object associated with the imagined movement increased corticospinal excitability to a greater extent than motor imagery performed alone.

The amplitude of motor-evoked potentials (MEPs) elicited using transcranial magnetic stimulation (TMS) has been shown to decrease in the short interval prior to response initiation. The cause of this premovement MEP suppression is currently unclear and has been attributed to various processes such as preparation-related inhibition preventing the premature release of planned action or increasing signal-to-noise ratio to facilitate rapid response initiation. The present study explored whether the decrease in MEP amplitude is affected by the task requirements, using reaction time (RT) paradigms that differ in the timeline of preparation and initiation of a motor response. Participants completed simple RT (SRT), choice RT (CRT), and go/no-go (GNG) tasks, while TMS was applied at various times between the warning signal and go-signal. It was hypothesized that if MEP suppression relates to preparation level, the greatest suppression would be observed during the SRT and GNG tasks, as these paradigms encourage advance preparation and response inhibition. Conversely, if the reduction in corticospinal excitability is associated with facilitating response initiation processes, then suppression would be expected for all tasks, including the CRT paradigm in which preparation does not occur until presentation of the go-signal. Results showed MEP amplitudes decreased for all tasks as the go-signal approached; however, both the SRT and GNG had significantly greater MEP suppression 50 ms prior to, and coincident with the go-signal. These results indicate that the nature and origin of the suppression is likely multifactorial and relates to both preparatory and initiation-related processes, with the timeline and magnitude of suppression dependent on the nature of the task being executed. Impact StatementTranscranial magnetic stimulation was used to elicit motor-evoked potentials to examine the timeline of corticospinal activation during the instructed delay period for choice, simple and go/no-go reaction time tasks. For all tasks, corticospinal excitability was initially elevated compared to baseline, followed by a similar magnitude of early suppression. However, just prior to the go-signal, those tasks that allowed advance preparation showed additional suppression, providing novel information linking pre-movement corticospinal suppression to preparatory and inhibition processes.

Background. Pain influences motor function and has been proposed to reduce corticospinal and intracortical excitability. At the same time, performance can be maintained during pain, at the cost of increased perceived effort, a centrally generated signal reflecting resource engagement. Here, we tested whether contralateral thermal heat pain-related changes in corticospinal and intracortical excitability contribute to increased effort perception. Methods. In this preregistered transcranial magnetic stimulation (TMS) study, twenty-one healthy participants received single and paired pulse TMS at rest and during submaximal isometric right wrist flexions performed at 20% maximal peak force. Trials were conducted under a control condition or during contralateral thermal stimulation (painful or non-painful warm) applied to the left forearm. After each contraction, participants rated the intensity of their perceived effort. Corticospinal and intracortical excitability of the right wrist flexor was assessed at rest and during submaximal contractions. Results. Contralateral heat pain significantly increased perceived effort compared with the control and warm conditions. Contralateral heat pain did not reduce corticospinal or intracortical excitability. Conversely, contralateral heat pain increased corticospinal excitability, reflected primarily in decreased cortical silent period duration. Perceived effort was associated with the subjective experience of pain rather than with TMS-derived variables. Conclusions. These findings suggest that increased effort during contralateral heat pain cannot be attributed to inhibition of the primary motor cortex or the corticospinal pathway. The higher perceived effort in the presence of contralateral heat pain likely reflects the cognitive cost of pain rather than alterations in the transmission of the motor command.

Postural control depends on the ability to adapt motor responses to changing environmental and physiological conditions. Neuromuscular fatigue (NMF) is known to alter balance and muscle activation patterns, yet its effects on motor adaptation during whole-body postural tasks and on the persistence of learned strategies remain unclear. This study investigated whether localized NMF of the ankle dorsiflexors influences adaptation to a novel postural perturbation task and whether learning under fatigue induces persistent changes during subsequent re-exposure. Twenty-five healthy young adults were assigned to either a fatigue (FAT) or no-fatigue (NoFAT) group and completed two experimental sessions separated by 48-72 h allowing recovery from acute fatigue for fatigued group. Participants adapted to repeated mechanical perturbations while standing upright, while ground reaction forces and electromyographic activity of lower-limb muscles were recorded. NMF did not impair overall adaptation performance, as both groups exhibited similar reductions in performance error across practice. However, participants exposed to fatigue exhibited altered postural recovery dynamics, characterized by a reduced return toward the initial posture following perturbation release. These differences persisted during re-exposure on the subsequent day, despite the absence of acute fatigue. In parallel, NMF modified muscle activation and coactivation patterns involving both fatigued and non-fatigued muscles, several of which were retained during re-exposure. These findings indicate that the central nervous system preserves successful adaptation to postural perturbations under fatigue by reorganizing neuromuscular coordination and stabilization strategies. Learning under fatigue therefore influences not only immediate motor execution, but also shapes the longer-term representation of postural control strategies.

The ability to accurately perceive arm position is essential for motor control and depends on the integration of proprioceptive and visual information. However, how lifelong visual impairment (VI) affects position sense and its neural correlates remains unclear. We quantified arm position sense and associated cognitive-motor load in right-handed visually impaired (n = 7) and normally sighted (NS; n = 7) individuals using three bilateral arm position matching tasks: joint angle matching (JAM; internal coordinates), hand direction-distance matching (DDM; external coordinates), and mirror direction-distance matching (MDDM; external coordinates kinematically identical to JAM). Cognitive load was assessed using the contingent negative variation (CNV) from EEG recordings. VI participants exhibited reduced accuracy and precision of arm position sense in most conditions, and greater CNV magnitude, particularly in the left parietal cortex. Across both groups, performance was worse and CNV magnitude was greater in the DDM task compared with JAM, whereas JAM and MDDM yielded similar behavioral and neural outcomes. These findings indicate that (i) visual experience enhances arm position sense, and (ii) representing limb position in external coordinates imposes greater cognitive demands than encoding joint-based posture. The similarity between JAM and MDDM suggests that participants preferentially rely on internal representations when task kinematics permit.

Healthy young and older adults completed two randomized sessions of split-belt treadmill walking, with and without a concurrent cognitive task. When the single-task session occurred first, both age groups showed savings in step length asymmetry during re-adaptation one week later. However, performing the dual-task session first reduced savings, and this order-effect was greater in older adults compared to young adults. These findings suggest that cognitive load during initial motor adaptation interferes with savings, but once stored, locomotor readaptation is resilient to dual-tasking.

Sensory degradation with aging can impair balance control, partly by disrupting visual contributions to self-motion estimation. We investigated how aging affects the control of frontal plane center of mass (CoM) trajectories during walking with exposure to repeated visual perturbations. We hypothesized that aging would increase responses to visual perturbations and decrease adaptation to repeated visual perturbation exposure. We applied three visual perturbations to 14 healthy older (age: 75.0{+/-}2.4) and 16 younger adults (age: 23.4{+/-}3.9) walking on a treadmill: fixating a stationary target with the background moving to the right (MB), tracking a target moving rightward over a stationary background with head rotation (MT-HR), and tracking a moving target with eye movement only (MT-EM). Deviations of CoM position and foot placement due to the visual perturbations were assessed. Over the whole trial, the older adults exhibited larger CoM position variability in MB and MT-HR conditions. During visual perturbation epochs, both age groups deviated in the same direction except MB. In MB, the older adults deviated to an opposite direction after a few perturbation repetitions. Moreover, in MT-HR and MT-EM, the older adults deviated earlier than the younger adults and they deviated more in the MT-HR condition. This indicates that older adults exhibit reduced ability to accurately estimate self-motion through correction by other sensory modalities when exposed to visual perturbations. Over repeated perturbations, the older adults showed decreased CoM deviations in MT-EM, which suggests that they still maintain the capacity to downweight visual information after repeated exposure.

Interlimb skill generalization, defined as the transfer of a newly learned skill from the trained to the untrained limb, represents a fundamental aspect of human motor behavior with significant implications for rehabilitation and athletic training. Skill generalization is influenced by processes that drive learning and interact with the newly acquired memory. For instance, in our recent work, we reported that performing a secondary, cognitively demanding task immediately after a short skill-training session impaired skill generalization when the untrained arm was tested 24-hour later. This suggests that working memory (WM) interacts with the early stage of skill memory consolidation processes and thereby impacts skill generalization. Motivated by this finding, in the current study, we investigate how WM interacts with reactivated skill memory and its subsequent impact on skill generalization, tested 24 or 48-hour post skill training. We recruited right-handed young participants (n=95) who performed a fast, accurate reaching task with their dominant right arm during a short training session (50 trials) on Day-1. After 24-hour on Day-2, depending on the group type, participants had a brief skill reactivation session (10 trials or no reactivation) and then performed the WM task (or a control task) with their right arm. Interlimb generalization to the untrained left arm was assessed either immediately after the WM/control task on Day-2 or after a 24-hour gap on Day-3. We found that, engaging in the WM task (compared to the control task) after skill reactivation on Day-2 enhanced immediate generalization. Conversely, when generalization was tested 24-hour later on Day-3, the same WM engagement impaired skill generalization. These findings demonstrate that WM engagement during the post-reactivation phase has a time-dependent influence on interlimb generalization. WM can facilitate immediate generalization, possibly by sustaining neural processes that promote skill memory generalization across effectors. However, when a 24-hour time gap is introduced, generalization is disrupted following WM engagement, possibly because of interference between underlying neural processes involved in WM and reactivation-induced (re)consolidation of the skill memory. This study highlights the delicate interplay among WM, motor memory reactivation dynamics, and skill generalization and suggests a time-dependent interplay of neural processes critical for optimizing outcomes in motor learning and clinical rehabilitation protocols.

Sensorimotor adaptation is a motor learning process that contributes to movement flexibility and is thought to arise from the interaction of fast and slow adaptive processes. Evidence suggests that declarative memory contributes to adaptation through its influence on the fast process. Although adaptation deficits are common following stroke, the mechanisms underlying these deficits remain unclear. This study investigated differences in locomotor adaptation rate and forgetting between individuals with chronic stroke and age-matched controls and examined how these measures were associated with immediate declarative memory performance. Individuals with chronic stroke (n = 23) and age- and education-matched controls (n = 21) completed four 4-minute bouts of split-belt treadmill adaptation separated by rest breaks. Adaptation rate, adaptation magnitude, and forgetting were quantified from exponential fits to normalized step-length asymmetry data. Immediate declarative memory was quantified using the Repeatable Battery for the Assessment of Neuropsychological Status, and associations between adaptation measures and immediate declarative memory were evaluated using robust linear regression. Participants with stroke adapted less (p = 0.001) and more slowly (p = 0.039) than controls during early adaptation and forgot less of the adapted behavior during the first rest break (p = 0.024). Notably, poorer immediate declarative memory performance was associated with reduced forgetting during the initial rest break, irrespective of group assignment (p = 0.035). This relationship supports the hypothesis that declarative memory contributes to adaptation through a cognitively mediated fast process. These findings suggest that cognitive impairment contributes to altered adaptation following stroke and highlight the importance of considering cognitive factors when investigating motor learning mechanisms and rehabilitation outcomes in neurological populations.

Humans consistently decrease the amount of force they produce during isometric finger pressing in the absence of visual feedback, a phenomenon often called force drift. This decrease in force production has been attributed to limitations in working memory and/or adaptive neural control processes that minimize energy consumption. In this study, we investigated a potential peripheral reason for such force drifts: increases in the coefficient of friction between the fingertip and the surface it contacts due to changes in fingertip contact area as the fingertip hydrates under prolonged pressure. We investigated this possibility by eliciting force drifts from participants performing isometric pressing tasks against smooth glass, which shows the phenomenon of increasing contact area during prolonged contact, and a polymer which does not exhibit this phenomenon. We confirmed that the coefficient of friction only increased on the glass plate, however we did not observe a difference in force drifts between these two surfaces, although we found some evidence that force drift could be associated with coefficient of friction. Our findings suggest that factors other than peripheral changes in coefficient of friction are the primary drivers of force drifts.

Response inhibition, the ability to suppress contextually inappropriate actions, is a cornerstone of cognitive control and is commonly assessed using paradigms such as the go/no-go task. However, traditional go/no-go paradigms rely on binary outcomes such as commission errors, which offer limited insight into the dynamic, graded behavioral adjustments underlying successful stopping. The present study developed a novel mouse-tracking go/no-go paradigm with a dynamic start to capture inhibitory processes during ongoing execution. Twenty-three healthy young adults completed the task in two sessions separated by approximately one week to evaluate the test-retest reliability of standard behavioral measures (error rates and reaction times), and three kinematic features: path length, mean velocity, and mean acceleration. Results revealed robust differences between go and no-go trials across all measures. Successful inhibition was characterized by significantly shorter path lengths and reduced mean velocity and acceleration compared to go trials. Critically, all measures demonstrated moderate-to-good test-retest reliability across sessions, with intraclass correlation coefficients ranging from .75 to .85 for go trials and from .59 to .83 for no-go trials. These findings establish construct validity and psychometric reliability of the current mouse-tracking go/no-go paradigm. The demonstrated stability of these measures provides the methodological foundation for their use in cross-sectional, longitudinal, and intervention research targeting inhibitory control.

Muscle fatigue potentially interferes with proprioceptive afference from peripheral "movement sensors"-- the proprioceptors, which may hinder the crucial sensorimotor integration and thus locomotor performance. However, little is known about how muscle fatigue affects cortical processing of proprioceptive afference. Twenty-four healthy volunteers (30.7 {+/-} 6.5 yrs, 13 females) participated in the experiment, which included magnetoencephalography (MEG) recordings during ankle proprioceptive stimulation (2-Hz passive movements), and fatigue tasks comprised of isometric ankle plantar flexion. Corticokinematic coherence (CKC) between foot acceleration and MEG signals was examined before (PRE) and [~]3 min after (POST) the fatigue tasks to quantify the cortical proprioceptive processing. CKC peaked in the gradiometer pairs above the foot region of the primary sensorimotor (SM1) cortex in each participant. CKC strength did not show significant difference between PRE and POST at 2 Hz (0.30 {+/-} 0.12 vs. 0.30 {+/-} 0.14, p = 0.981) or its first harmonic at 4 Hz (0.38 {+/-} 0.14 vs. 0.37 {+/-} 0.13, p = 0.724). However, 4-Hz MEG power was [~]30% lower in POST than in PRE. Surprisingly, fatigue-induced bilateral increase of alpha and beta power was observed in SM1 hand regions during the movement stimulation. Our results indicated that the early processing of proprioceptive afference from the ankle joint was negligibly affected by muscle fatigue, or it recovered rapidly. The effects of muscle fatigue on the proprioceptive processing appear to extend beyond the primary somatotopic regions to bilateral SM1 neuronal networks. This cortical adaptation to muscle fatigue potentially preserves proprioceptive processing by modulating SM1 inhibitory neurons, offering a novel perspective for future research on proprioception.

Pain demands attention and can disrupt task-related goals. Attention allocation is a key cognitive process supporting motor learning and disruption of internal schemas associated with attentional control during motor learning can result in interference in improvements in performance. Movement-contingent pain is an important characteristic of persistent musculoskeletal pain. Despite this, research exploring pain interference with motor learning and attention has exclusively utilised tonic pain paradigms. Understanding the impacts of movement-contingent pain on motor learning and attention may provide important insights into the interaction between pain and motor learning. The aim of this study was to; 1) explore the robustness of a movement-contingent pain paradigm across an extended period of training, 2) explore the impact of movement-contingent pain on improvements in performance and attentional allocation during motor learning. Three groups (healthy non-pain, healthy experimental-pain and persistent pain experimental-pain) completed ten trials of a motor sequence learning task while experiencing a movement-contingent electrical stimulation. Three task performance measures and five gaze indices, previously associated with attentional control, were collected. Results showed that; 1) low frequency electro-cutaneous stimulation could produce a valid and consistent pain experience across a sustained period of training, 2) attentional allocation becomes more efficient across learning, accompanied by improvements in task performance, 3) changes in task performance and attentional measures across training were similar in all groups despite the presence of pain, 4) movement-contingent experimental pain enhanced spatial performance at all time points in healthy participants but was not accompanied by a different pattern of attentional allocation. This study demonstrates that the impact of movement-contingent pain on motor learning is comparable to the impacts of tonic experimental pain and provides interesting insights into patterns of attentional allocation across time but little evidence that these attentional allocations are impacted by the presence of pain or a past history of pain.

BackgroundExplosive force generation during the initial acceleration phase is critical for successful base stealing in baseball. Preparatory balance control preceding movement onset may facilitate this process by constraining horizontal ground reaction force (GRF) toward a task-specific direction. However, its contribution to ballistic sprint initiation remains unclear. Research questionDoes preparatory force constraint influence explosive force generation during base stealing, and when during the preparatory phase is this influence greatest? MethodsFourteen baseball players performed 3-m maximal sprints simulating base stealing under time-constraint (Time) and self-paced (Self) conditions. GRF around movement onset were recorded. Peak rate of force development (peak RFD) was computed from onset to take-off. A 250-ms window before the onset was divided into 50-ms bins, and mean resultant length (Rlen), which represents the extent of force constraint, of each bin was calculated. Using statistics analyses, Differences between conditions were tested, and the relationship between the interaction (Rlen x condition) and peak RFD was assessed. ResultsThe peak RFD was greater under the Self condition than under the Time condition, accompanied by a larger Rlen. Furthermore, Results indicated that the force constraint in the 150-100 ms interval preceding the movement onset most strongly influenced the peak RFD. SignificanceThese findings demonstrate that temporally organized preparatory force constraint plays a critical role in explosive sprint initiation during base stealing. Identifying the specific preparatory timing linked to superior force production provides novel mechanistic insight into preparatory balance control and may inform targeted training strategies for ballistic athletic movements.

Artificial limbs typically lack somatosensory receptors, limiting users' access to haptic feedback about movement outcomes. However, indirect tactile signals generated during object interaction are transmitted to the body-limb interface and may serve as a haptic feedback source. This study investigates whether such indirect tactile signals convey distinct information that can support localisation of touch on an artificial body part. Using an additional robotic thumb (The Third Thumb, Dani Clode Design), we measured tactile signals at the interface between the Third Thumb and the hand following stimulation from four vibration motors positioned along the Thumb. We then assessed whether participants could discriminate these signals and integrate them with different Thumb postures to spatially localise touch. Measurements showed that each stimulation site produced distinct tactile signatures at the interface. Behaviourally, participants localised touch at above-chance levels. Representational similarity analyses further revealed that performance was best explained by the spatial positions of stimuli, rather than by limb-based coordinates or indirect signal patterns alone, indicating flexible mapping of indirect touch signals onto the Third Thumb posture. Together, these findings demonstrate that indirect tactile signals transmitted through an artificial limb can be discriminated and flexibly remapped to support spatial localisation of touch.

Internal forward models predict the sensory consequences of motor commands; however, whether the anticipated availability of post-action feedback contributes to the precision of the action itself remains unknown. We manipulated the predictability of post-release visual occlusion in skilled basketball players. Participants performed three-point shots while wearing liquid-crystal shutter goggles. The study tested three conditions: a no-occlusion baseline, certain-occlusion condition in which players knew that their vision would be occluded at ball release in every trial, and random-occlusion condition in which they could not predict whether an occlusion would occur. Shooting accuracy declined in the certain-occlusion condition relative to the no-occlusion condition (49.2% vs 41.7%). The random-occlusion condition did not differ from the baseline (46.1%). Within the random condition, the accuracy in occluded trials were virtually identical to that in non-occluded trials (46.6% vs 46.2%), even though the immediate visual occlusion was the same as in the certain-occlusion condition. These results demonstrate that it is not the absence of post-action information per se that disrupts motor execution, but the prior certainty that action consequences will be unavailable. We interpret this finding as a prospective influence of anticipated consequence loss, whereby motor execution depends on whether the prediction-outcome loop remains closable.

ImportanceRecovery after upper extremity peripheral nerve injury (PNI) surgery depends on changes in cortical neural patterns that support sensorimotor control. Task-based functional connectivity (FC) can characterize these changes, yet few studies have explored FC during ecologically fine motor valid tasks after PNI. ObjectiveTo investigate task-based FC with the left primary motor cortex (M1) during right hand drawing in individuals following right hand PNI surgery. ParticipantsForty-four right-handed adults, including 12 patients post PNI surgery (n = 8 with nerve repair, n = 4 with nerve transfer) and 32 healthy controls. MethodsAll participants underwent fMRI while performing a RH visuomotor precision drawing task. Seed-based connectivity analysis was performed to characterize the pattern of FC between left M1 and all voxels in the brain. We hypothesized that left M1 FC would differ between patients and controls, between Repair and Transfer groups, and covary with time since surgery. ResultsPatients (vs. controls) showed greater FC between left M1 and right visual and premotor cortices. Nerve transfer (vs. repair) showed greater FC between left M1 and right inferior parietal areas. Time since surgery was not linearly related to FC, though exploratory analyses suggested a negative association between log-time and FC between left M1 and right inferior parietal lobule. ConclusionAfter PNI surgery, visuomotor precision drawing involved distinct and behaviorally relevant neural patterns, which varied by task demand and potentially by surgical group despite clinical heterogeneity. Inferior parietal cortex may be especially engaged in early months after surgery (i.e. log-time). To improve recovery of upper limb function after PNI, clinical recommendations include incorporating early function-specific dexterous training, tailoring rehabilitation across surgical and recovery stages, and using multidimensional assessments of hand function.