Experimental Brain Research

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.

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.

Motor skills such as bicycle riding are considered robust and transferable across bicycle types. However, when the steering direction is inverted (reversed bicycle) control is disrupted to the extent that the bicycle cannot be ridden. With sufficient practice, the reversed bicycle can be learned, but this learning appears to produce impairment of normal bicycle riding suggesting modification of this long-established motor memory. Here we investigate the learning process of riding a reversed bicycle over four days of practice, while repeatedly assessing normal bicycle performance to measure any potential interference. Introduction of the reversed bicycle disrupted predictive control, reflected in a consistently increased time lag in the steering-roll coupling during reversed bicycle trials. This increase in delay suggests that predictive behavior in normal bicycle riding cannot be transferred to the reversed bicycle. With training, some participants successfully learned to ride the reversed bicycle by gradually reorganizing this coupling, whereas others failed to acquire this inverted coupling. Notably, even short-term exposure to the reversed bicycle interfered with normal bicycle riding, reducing distance ridden and increasing variability in steering rate. Together, we show that even a highly practiced whole-body motor skill is susceptible to rapid interference when control dynamics are altered.

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.

Freezing of gait is a disabling episodic symptom of Parkinson's disease, typically emerging during complex locomotor tasks such as turning, obstacle negotiation, and gait initiation. These tasks require effective motor planning and proactive visual search of the intended walking route. Current evidence suggests that people with Parkinson's disease and freezing of gait show different patterns of visual search compared to those without freezing of gait and healthy older adults. However, existing reports are based on relatively simple tasks that lack common triggers for freezing of gait and do not adequately control for other factors likely to influence visual search, such as motor symptom severity and balance ability. This study examined visual search behaviour in 24 healthy older adults and 37 people with Parkinson's disease (21 with freezing of gait, 16 without) during a complex walking task requiring repeated turning and navigation through narrow spaces. Visual search characteristics were compared between people with Parkinson's disease and healthy controls, and relationships between visual search, freezing of gait, motor symptom severity, and balance ability were explored within the Parkinson's disease group. Compared with healthy controls, people with Parkinson's disease showed significantly fewer fixations toward areas outside the walking path, longer average fixation durations, and reduced saccade amplitudes, with no differences in proactive visual planning of the intended route. No relationship was found between visual search outcomes and freezing of gait. Reduced fixations to outside-path areas were associated with poorer functional balance independently of motor symptom severity. These findings indicate that restricted visual sampling in Parkinson's disease is primarily associated with balance impairment rather than freezing of gait or motor symptom severity.

Voluntary contraction in one limb can facilitate motor output in a distant limb, a phenomenon commonly referred to as the remote effect. However, the neural mechanisms underlying this remote interlimb facilitation remain unclear. This study investigated cortical and spinal contributions to the remote effect in able-bodied participants. Transcranial magnetic stimulation (TMS) was applied over the hand area of the primary motor cortex using posterior-anterior (PA) and anterior-posterior (AP) current directions, which are sensitive to different cortical inputs. Cortical excitability was assessed using single- and paired-pulse paradigms to measure short-interval intracortical inhibition (SICI), short-interval intracortical facilitation (SICF), and short-latency afferent inhibition (SAI). Spinal motoneuron excitability was assessed from F-waves elicited by peripheral nerve stimulation. During voluntary lower-limb contractions, single-pulse TMS elicited larger motor evoked potentials in hand muscles across current directions, indicating a broad increase in net corticospinal output. However, only AP-sensitive paired-pulse measures showed reduced SICI and enhanced SICF during contraction, whereas PA-sensitive SICI and SICF were not significantly altered, suggesting that cortical modulation during the remote effect is expressed more clearly in AP-sensitive measures. SAI with PA stimulation was less consistently expressed during contraction, suggesting that afferent-related inhibitory modulation may also be influenced during the remote effect. In parallel, F-wave amplitude and persistence increased, consistent with enhanced spinal motoneuron excitability. Together, these results provide converging evidence that the remote effect in humans involves broad corticospinal and spinal facilitation, accompanied by current direction-dependent modulation of cortical excitability measures. KEY POINTS SUMMARYO_LIVoluntary contraction in one limb can facilitate motor output in a distant limb, but the mechanisms underlying this remote interlimb facilitation remain unclear. C_LIO_LIWe tested whether remote lower-limb contraction modulates corticospinal output, intracortical excitability, and spinal motoneuron excitability in a resting hand muscle. C_LIO_LISingle-pulse transcranial magnetic stimulation showed that motor evoked potentials in the hand were facilitated during remote lower-limb contraction across multiple current directions, indicating a broad increase in net corticospinal output. C_LIO_LIPaired-pulse measures were modulated preferentially with anterior-posterior stimulation, with reduced short-interval intracortical inhibition and increased short-interval intracortical facilitation, suggesting current direction-dependent modulation of cortical excitability measures. C_LIO_LIF-wave amplitude and persistence were also enhanced during remote lower-limb contraction, indicating increased spinal motoneuron excitability. These findings provide converging evidence that the remote effect involves both cortical and spinal contributions. C_LI

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.

Summary paragraphA hallmark of learning is the need for sensory stimuli (Ginns, 2015; McGraw et al., 2009; Reinwein, 2012; Spence, 1950) so that learning is fundamentally based on sensory input signals affecting behaviour, physiology, and neurology. If behavioural measures of learning can be causally linked to physiological and neurological variables, a broader understanding of the mechanisms related to learning in schools, learning disabilities, and learning and health issues may emerge (McGraw et al., 2009). Despite decades of research on the physiological/neurological variable of sympathetic activation, learning, and achievement (Horvers et al., 2021), any causal relation remains unclear (Cowley et al., 2014; Mason et al., 2020; Pijeira-Diaz et al., 2016; Sung et al., 2023; Yu et al., 2024) and issues with instrument validation remain (Costantini et al., 2023; Hu et al., 2024; Milstein & Gordon, 2020; Van Der Mee et al., 2021). Here we investigate the effect of sensory input on sympathetic activation by using validated instruments for skin conductance measurement (Batista et al., 2019) and whether sympathetic activation is connected to learning in a cognitive laboratory context and an ecologically valid classroom context. In both contexts, we found a physiological variable which correlated with learning and that sensory input affected this variable while student movement did not. These sensory inputs varied depending on the different instructional activities the students participated in. Together, these findings bring us one step closer to a model linking sensory input to behavioural, physiological, and neurological variables.

BACKGROUND: Dual task walking requires simultaneous management of cognitive and motor demands and is associated with changes in gait and cortical activation. However, the relationship between task related cortical recruitment and dual task related gait adjustments in healthy young adults remains unclear. This study aimed to investigate the effects of dual tasking on gait performance and cortical activation, and to examine the association between changes in cortical activity and dual-task costs. METHODS: This cross sectional study included 33 healthy young adults. Participants performed three conditions: single task walking, cognitive single task (verbal fluency), and dual task walking. Each condition was repeated 10 times using a repeated short block design with randomized trial presentation. Gait performance was assessed using an instrumented walkway, and cortical activation was measured using functional near infrared spectroscopy. Dual task costs were calculated for gait and cognitive outcomes. Statistical analysis included repeated measures analysis of variance (ANOVA) and Wilcoxon signed rank tests, with false discovery rate correction for multiple comparisons. Associations between changes in cortical activation and dual task costs were examined using correlation analyses. RESULTS: Dual task walking resulted in significant changes in gait, including reduced speed, step and stride length, and increased base of support, stance, and double support (all p < 0.05), while cognitive performance remained unchanged. Dual tasking was associated with increased cortical activation in left prefrontal and motor related regions. Greater increases in cortical activation were associated with lower dual task costs across most gait parameters, with significant correlations observed in the left dorsolateral prefrontal cortex (r {approx} 0.42 to 0.47 for speed and stride length; p < 0.05). Double support showed a distinct pattern, suggesting a specific temporal adjustment within the gait cycle. CONCLUSIONS: Dual task walking in young adults is associated with coordinated behavioral and cortical adaptations. Increased cortical recruitment is linked to reduced motor interference, suggesting that broader engagement of cortical networks may contribute to performance under cognitive motor load.

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.

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.

Mental rotation in 3D is a key cognitive skill involving dynamic spatial transformations, for which pronounced individual differences have been documented. Here we ask whether individual differences in 3D abilities can be explained by analogous differences in 2D abilities. 3D mental-rotation was assessed by the Vandenberg & Kruse Mental Rotation Test (3D-MRT) and examined for association with performance and underlying electrocortical mechanisms during a 2D letter rotation task. Participants (N=40) first completed the MRT and then performed a computerized 2-D letter rotation task in which they had to identify whether letters were oriented in a standard or a mirrored direction (parity judgment) when rotated at 0{degrees}, 60{degrees}, 120{degrees}, and 180{degrees} while EEG was recorded. Reaction times (RTs) and error rates increased with angular disparity. The angular disparity effect on RT was smaller for mirrored letters. Low, relative to high, 3D-MRT scoring participants showed more pronounced accuracy declines at higher rotation angles. An EEG Event Related Potential (ERP) known as the Rotation-Related Negativity (RRN) became more pronounced with increasing angular disparity. High 3D-MRT scores were associated with a stronger RRN response at central-parietal sites. In addition, the ERP-P3b wave was more pronounced at central-parietal sites for low 3D-MRT scorers, independent of angular disparity. It is concluded that 3D rotational ability is positively associated with 2D mental rotation performance, and more strongly with enhanced recruitment of neural visual-spatial cortical representations than with enhanced recruitment of more general cognitive resources.

Purposeto characterize the dynamic postural control during weight load shifting with and without support surface reduction with temporal metrics commonly used in linear control systems identification. MethodsFrom the COP coordinates temporal, global and structural parameters were calculated. Reliability of derived parameters were determined using Bland-Altman analysis. ResultsFor the observed population, temporal variables tend to decrease when the complexity of the task is increased with the reduction in the support surface and the non dominance. ConclusionDelay and rise times were significantly shorter for the non-dominant limb in the anteroposterior direction when volunteers performed the same task with different limbs. In the mediolateral direction, delay and rise times were shorter in both unipodal stances with respect to their bipodal homologues. An increase in COP path length, velocity and sample entropy was observed when the support area was reduced. All parameters showed good reliability in both directions at all stances. This framework could be used in the clinical practice to assess dynamic postural control capabilities in patients whose balance is pathologically affected. The trial was evaluated and approved by the Central Committee of Bioethics in Biomedical Practice and Research of the province of Entre Rios.

Gait asymmetry is a common manifestation of walking impairment among clinical populations. We recently developed a novel treadmill walking approach called dynamic treadmill walking that can provide asymmetric gait training by changing the treadmill speed between fast and slow speeds within a single stride. Here, we studied the energy expenditure associated with a variety of dynamic treadmill walking conditions. We hypothesized that the metabolic power required for dynamic treadmill walking in all conditions would approximate the metabolic power associated with conventional walking at the mean of the fast and slow speeds employed in the task. Eleven young adults without gait impairment walked on an instrumented treadmill and breathed into a metabolic measurement system. During dynamic treadmill walking, the treadmill fluctuated between 0.75m/s and 1.50m/s, each for 50% of an individuals stride time. We used a metronome to synchronize participants right heel-strikes with four different timing conditions. Net metabolic power during dynamic treadmill walking was significantly greater than normal walking at the mean speed of the task (1.125m/s) and generally lower than walking at the fast speed (1.5m/s). We did not observe any significant associations between net metabolic power and several measures of gait asymmetry during dynamic treadmill walking. These findings establish dynamic treadmill walking as a promising technique for improving gait symmetry in individuals who cannot tolerate fast treadmill walking, a common gait rehabilitation approach. Future work will assess the feasibility, metabolic demands, and clinical efficacy of using dynamic treadmill walking to improve gait symmetry in clinical populations. Key Points SummaryO_LIDynamic treadmill walking (i.e., walking with oscillating treadmill speeds) has previously been shown to drive gait asymmetries, but little is known about the energy expenditure required to complete the task. C_LIO_LIOur hypothesis was that dynamic treadmill walking would have similar metabolic power requirements to normal walking at a speed that is intermediate between the two dynamic treadmill walking speeds. C_LIO_LIWe found that dynamic treadmill walking actually requires metabolic power that is greater than the average of the two belt speeds, but less than that used for fast walking. C_LIO_LIDynamic treadmill walking is a promising and clinically translatable technique for rehabilitating populations with gait asymmetries that is not more energetically costly than fast treadmill walking, a common gait rehabilitation approach. C_LI

Flow state, characterized by optimal engagement and performance, represents a key concept in understanding human performance and cognitive resource allocation. Grounded in Csikszentmihalyis and Sherrys flow theory and the Limited Capacity Model of Motivated Mediated Message Processing (LC4MP), this study investigated physiological and neural correlates of flow state during a simulated driving task under different music conditions and difficulty levels. Using a 2 x 3 factorial design with 20 participants, this study examined self-selected versus non-self-selected music across three difficulty levels, testing the relationship between task switching, cognitive resource allocation, and flow state. Physiological measures included heart rate and EEG (alpha/theta power) using a 4-channel Muse 2 headband, alongside a self-report measure of flow experience. Hierarchical linear modeling revealed significant physiological changes during self-selected music: heart rate decreased ({beta} = -5.15, p < .001), while alpha ({beta} = 5829.77, p < .001) and theta power ({beta} = 7637.24, p < .001) increased. Task difficulty also showed significant effects, with heart rate decreasing during hard ({beta} = -6.70, p < .001) and moderate ({beta} = -3.40, p = .001) conditions. In particular, while physiological measures showed robust changes, the self-reported flow state did not reach significance. Task switching rates showed significant decreases during self-selected music ({beta} = -0.86, p < .001) and hard difficulty ({beta} = -0.61, p < .001), supporting the LC4MP frameworks predictions regarding cognitive resource allocation. These findings demonstrate how task switching and cognitive resource allocation relate to flow state induction. The results highlight the importance of multimodal measurement approaches and demonstrate that personal relevance through music selection and task difficulty significantly influence physiological and neural responses during performance. Future research should employ more comprehensive measurement approaches to better capture the complexity of flow-related neural activity and its relationship to task switching and cognitive resource allocation.

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.

Ankle clonus is a sustained, involuntary, rhythmic muscle contraction frequently observed in humans with spinal cord injury (SCI). Although its pathophysiology remains incompletely understood, converging evidence suggests a role for brainstem systems in its generation. Following SCI, brainstem neuromodulatory inputs partially compensate for the loss of descending motor pathways by regulating motoneuron excitability during involuntary contractions, suggesting their involvement in the generation of clonus. To test this hypothesis, motoneuron excitability in response to Ia synaptic input was quantified using the soleus H reflex and maximal motor response (H/M ratio), and brainstem involvement was probed using the long lasting component of the cutaneous reflex (LLR) in the tibialis anterior and soleus muscles, as well as the StartReact response-an involuntary release of a movement triggered by a startling stimulus thought to engage the reticulospinal tract. We studied individuals with chronic SCI, both with and without ankle clonus, using standardized clinical tests across two days. Participants with clonus showed elevated H/M ratios, indicating increased motoneuron excitability, whereas those without clonus exhibited lower values than controls. Additionally, individuals with clonus exhibited longer LLR duration and greater LLR magnitude in both muscles, along with shorter reaction times to startle stimuli, consistent with enhanced monoaminergic and reticulospinal contributions. Notably, LLR duration was positively correlated with both StartReact response and H/M ratio. Together, these findings support a role for descending brainstem systems-particularly monoaminergic and reticulospinal pathways-in the maintenance of clonus in chronic SCI.

Elite athletes exhibit sport-specific neural adaptations, yet it remains unclear whether such changes reflect general effects of training or the unique demands of individual sports. Skiing requires postural control and whole-body coordination under dynamically unstable environments, placing high demands on somatosensory processing and sensorimotor integration. The present study aimed to identify structural brain characteristics specific to elite skiers by comparing them with athletes from other sports disciplines and non-athletes. T1-weighted MRI data were analyzed using voxel-based morphometry in 13 skiers, 23 non-ski control athletes and 25 non-athletes. Whole-brain analysis comparing skiers with non-ski athletes revealed a significant cluster showing greater gray matter volume in skiers compared with non-ski athletes in the left postcentral gyrus, extending into the superior parietal lobule. The identified cluster primarily encompassed cytoarchitectonic Areas 2 and 5L. These regions are involved in higher-order somatosensory processing and multisensory integration. Importantly, region-of-interest analysis demonstrated that gray matter volume within this cluster was greater in skiers compared with non-ski athletes and non-athletes, with no difference between non-ski athletes and non-athletes. These findings highlight the relative prominence of structural adaptations within somatosensory-parietal networks, reflecting the unique integration of proprioceptive and other sensory information required for elite skiing. Overall, these findings provide evidence for sport-specific structural brain differences in elite athletes and highlight the importance of somatosensory and parietal regions in sensorimotor integration relevant to skiing. These findings may have implications for understanding neural markers of expertise and may inform future approaches to training and performance evaluation in skiing.

BackgroundActivities of Daily Living (ADL) assessments are essential outcome measures in rehabilitation and long-term care, but primarily focus on task completion and provide limited insight into the postural control structures underlying movement failure. This paper proposes the Four Movement Screen Structure (4MS), a theoretical framework that reconceptualizes human movement control through four postural control phases: supine, sitting, standing, and single-leg standing. The framework proposes that functional decline may present with non-continuity, asymmetry, and compensatory preservation, rather than a simple reversal of motor development. MethodsAn exploratory, hypothesis-generating cross-sectional study was conducted with 297 certified care recipients (mean age 80.5 years) across multiple day-service facilities in Japan. Each participant was assessed using both the Barthel Index (BI) and the 4MS evaluation. Descriptive statistics, Pearson correlations, chi-square tests, and Fishers exact tests were used to explore the structural properties of the framework. ResultsThe mean BI total was 89.0 (SD = 13.8); the mean 4MS total score was 7.75 (SD = 2.02). A moderate positive correlation was found between BI total and 4MS total score (r = 0.471, p < 0.001, 95% CI [0.378, 0.555]). Of the five defined decline types, four were observed: mixed (57.6%), supine-dominant (21.2%), standing-dominant (5.7%), and single-leg-dominant (15.5%); sitting-dominant was not observed. The supine phase was the primary intervention target in 74.4% of cases--a finding we term the "supine paradox." In a subsample of 274 participants, 90.0% of those in the low supine score group (0-1.0, n = 170) performed rising from supine independently, suggesting that this paradox reflects qualitative deficits in foundational motor control masked by compensatory strategies. ConclusionsThese exploratory findings are broadly consistent with the non-reversal hypothesis and suggest that 4MS may capture structural dimensions of postural control not fully represented by conventional ADL assessment. As a hypothesis-generating study, these findings should be interpreted as generating testable hypotheses for future longitudinal and interventional research. Keywords: Postural control; Activities of daily living; Motor development; Functional decline; Barthel Index; Long-term care; Supine paradox; Non-reversal hypothesis; Geriatric assessment; Exploratory study

PurposeTranscranial direct current stimulation (tDCS) can noninvasively modulate activity in targeted brain regions. It is well established that the excitability of motor-related regions can increase when the target region is located beneath the anode (anodal tDCS), suggesting its potential to increase motor performance. Although such attempts have been widely examined, the results remain inconclusive. The purpose of this study was to assess the conditions under which anodal tDCS may improve motor performance in healthy adults. MethodsWe conducted a systematic review of studies on the use of anodal tDCS for improving motor performance in healthy adults. A computerized search was performed using the Web of Science, Scopus, PubMed, JDreamIII, and Ichushi-Web to identify relevant studies published between January 1, 1990 and May 25, 2022. ResultsTwenty-five studies were included in the qualitative synthesis. For the meta-analysis, 25 trials (N=885) were extracted from 23 studies. There were significant effects of anodal tDCS on motor performance improvement, but with evidence of publication bias and substantial heterogeneity among the trials. Post-hoc analysis revealed that motor performance 24 hours after the application of anodal tDCS may benefit from stimulation. There was no marked effect related to stimulation intensity, duration, or whether stimulation was provided during motor performance. ConclusionsOur study clarified the current state of anodal tDCS use for motor performance enhancement and indicates that there is currently no reliable evidence to support its effectiveness. Further studies, particularly randomized controlled trials, are necessary to establish the reliability of these effects for future applications.