Role of cerebral cortex in human postural control: an EEG study

Unraveling the threads of stability: A review of the neurophysiology of postural control in Parkinson's disease

Postural instability is a detrimental and often treatment-refractory symptom of Parkinson's disease. While many existing studies quantify the biomechanical deficits among various postural domains (static, anticipatory, and reactive) in this population, less is known regarding the neural network dysfunctions underlying these phenomena. This review will summarize current studies on the cortical and subcortical neural activities during postural responses in healthy subjects and those with Parkinson's disease. We will also review the effects of current therapies, including neuromodulation and feedback-based wearable devices, on postural instability symptoms. With recent advances in implantable devices that allow chronic, ambulatory neural data collection from patients with Parkinson's disease, combined with sensors that can quantify biomechanical measurements of postural responses, future work using these devices will enable better understanding of the neural mechanisms of postural control. Bridging this knowledge gap will be the critical first step towards developing novel neuromodulatory interventions to enhance the treatment of postural instability in Parkinson's disease.

The Effect of Sensory Reweighting on Postural Control and Cortical Activity in Parkinson's Disease

Aims

Balance requires the cortical control of visual, somatosensory, and vestibular inputs. The aim of this cross-sectional study was to compare the contributions of each of these systems on postural control and cortical activity using a sensory reweighting approach between participants with Parkinson's disease (PD) and controls.

Methods

Ten participants with PD (age: 72 ± 9; 3 women; Hoehn & Yahr: 2 [1.5 - 2.50]) and 11 controls (age: 70 ± 3; 4 women) completed a sensory organization test in virtual reality (VR-SOT) while cortical activity was being recorded using electroencephalography (EEG). Conditions 1 to 3 were completed on a stable platform; conditions 4 to 6 on a foam. Conditions 1 and 4 were done with eyes open; conditions 2 and 5 in a darkened VR environment; and conditions 3 and 6 in a moving VR environment. Linear mixed models were used to evaluate changes in center of pressure (COP) displacement and EEG alpha and theta/beta ratio power between the two groups across the postural control conditions. Condition 1 was used as reference in all analyses.

Results

Participants with PD showed greater COP displacement than controls in the anteroposterior (AP) direction when relying on vestibular input (condition 5; p<0.0001). The mediolateral (ML) COP sway was greater in PD than in controls when relying on the somatosensory (condition 2; p = 0.03), visual (condition 4; p = 0.002), and vestibular (condition 5; p < 0.0001) systems. Participants with PD exhibited greater alpha power compared to controls when relying on visual input (condition 2; p = 0.003) and greater theta/beta ratio power when relying on somatosensory input (condition 4; p = 0.001).

Conclusions

PD affects reweighting of postural control, exemplified by greater COP displacement and increased cortical activity. Further research is needed to establish the temporal dynamics between cortical activity and COP displacement.

Discrete cortical control during quiet stance revealed by desynchronization and rebound of beta oscillations

Postural sway during quiet stance often exhibits a repetition of micro-fall and the subsequent micro-recovery. The classical view -that the quiet bipedal stance is stabilized by the ankle joint stiffness- has been challenged by paradoxical non-spring-like behaviors of calf muscles: gastrocnemius muscles are shortened and then lengthened, respectively, during the micro-fall and the micro-recovery. Here, we examined EEG based brain activity during quiet stance, and identified desynchronization and synchronization of beta oscillations that were associated, respectively, with the micro-fall and the micro-recovery. Based on a widely accepted scenario for beta-band desynchronization during movement and post-movement rebound in the control of discrete voluntary movement, our results reveal that the beta rebound can be considered as a manifestation of stop command to punctuate the motor control for every fall-recovery cycle. Namely, cortical interventions to the automatic postural control are discrete, rather than continuous modulations. The finding is highly compatible with the intermittent control model, rather than the stiffness control model.

Effect of psychostimulant medications on static balance performance in adults with attention deficit hyperactivity disorder: Within-subjects repeated-measure study

OBJECTIVE

This study examined the effect of psychostimulant medications nPS) on balance and functional motor performance in adults with attention-deficit/hyperactivity disorder (ADHD).

METHODS

Participants completed two sessions (off-medication and on-medication) in a within-subjects repeated-measure study design. There was a minimum of seven days between the two sessions. During both sessions, participants stood for 30 s per condition on a force platform. The conditions were: feet-apart with 1) eyes-open and 2) eyes-closed; feet-together with 3) eyes-open and 4) eyes-closed. Participants performed three trials of timed up and go (TUG) and lateral step-up test (LSUT) during both sessions. Outcome measures were sway area (SA [cm²]), average sway velocity (SV [cm/s]), TUG average time (s), and average number of LSUT repetitions. Data were analyzed using multivariate repeated measures analysis of variance and paired t-tests for examining PS effects on balance (SA and SV) and functional motor performance (TUG and LSUT), respectively.

RESULTS

The sample included 45 adults (35 females; mean age = 28.4 ± 6.3 years). The repeated-measures MANOVA indicated that PS was associated with better SA [F(1,44) = 9.6; p = 0.003;η_p² = 0.18] but not with SV [F(1,44) = 1.0; p = 0.319;η_p² = 0.02]. PS was associated with significantly better SA with decreasing base-of-support [F(1,44) = 9.9; p = 0.003;η_p² = 0.18]. Additionally, PS use was associated with better TUG [t(1,44) = 2.65; p = 0.014;Cohen's d = 0.39] but not LSUT performances [t(1,44) = -0.68; p = 0.499;Cohen's d = -0.10].

CONCLUSIONS

PS was associated with better SA and TUG in adults with ADHD. Further studies are needed to investigate the effects of PS on balance performance using rigorous designs in this population.

IMPACT

Healthcare providers should screen for PS status and balance when treating adults with ADHD to enhance safe motor performance.

Predicting postural control adaptation measuring EEG, EMG, and center of pressure changes: BioVRSea paradigm

Introduction: Postural control is a sensorimotor mechanism that can reveal neurophysiological disorder. The present work studies the quantitative response to a complex postural control task. Methods: We measure electroencephalography (EEG), electromyography (EMG), and center of pressure (CoP) signals during a virtual reality (VR) experience called BioVRSea with the aim of classifying different postural control responses. The BioVRSea paradigm is based on six different phases where motion and visual stimulation are modulated throughout the experiment, inducing subjects to a different adaptive postural control strategy. The goal of the study is to assess the predictability of those responses. During the experiment, brain activity was recorded from a 64-channel EEG, muscle activity was determined with six wireless EMG sensors placed on lower leg muscles, and individual movement measured by the CoP. One-hundred and seventy-two healthy individuals underwent the BioVRSea paradigm and 318 features were extracted from each phase of the experiment. Machine learning techniques were employed to: (1) classify the phases of the experiment; (2) assess the most notable features; and (3) identify a quantitative pattern for healthy responses. Results: The results show that the EEG features are not sufficient to predict the distinct phases of the experiment, but they can distinguish visual and motion onset stimulation. EMG features and CoP features, when used jointly, can predict five out of six phases with a mean accuracy of 74.4% (±8%) and an AUC of 0.92. The most important feature to identify the different adaptive strategies is the Squared Root Mean Distance of points on Medio-Lateral axis (RDIST_ML). Discussion: This work shows the importance and the feasibility of a quantitative evaluation in a complex postural control task and demonstrates the potential of EEG, CoP, and EMG for assessing pathological conditions. These predictive systems pave the way for developing an objective assessment of pathological behavior PC responses. This will be a first step in identifying individual disorders and treatment options.

Brain activity during dual-task standing in older adults

Background

In older adults, the extent to which performing a cognitive task when standing diminishes postural control is predictive of future falls and cognitive decline. The neurophysiology of such “dual-tasking” and its effect on postural control (i.e., dual-task cost) in older adults are poorly understood. The purpose of this study was to use electroencephalography (EEG) to examine the effects of dual-tasking when standing on brain activity in older adults. We hypothesized that compared to single-task “quiet” standing, dual-task standing would decrease alpha power, which has been linked to decreased motor inhibition, as well as increase the ratio of theta to beta power, which has been linked to increased attentional control.

Methods

Thirty older adults without overt disease completed four separate visits. Postural sway together with EEG (32-channels) were recorded during trials of standing with and without a concurrent verbalized serial subtraction dual-task. Postural control was measured by average sway area, velocity, and path length. EEG metrics included absolute alpha-, theta-, and beta-band powers as well as theta/beta power ratio, within six demarcated regions-of-interest: the left and right anterior, central, and posterior regions of the brain.

Results

Most EEG metrics demonstrated moderate-to-high between-day test–retest reliability (intra-class correlation coefficients > 0.70). Compared with quiet standing, dual-tasking decreased alpha-band power particularly in the central regions bilaterally (p = 0.002) and increased theta/beta power ratio in the anterior regions bilaterally (p < 0.001). A greater increase in theta/beta ratio from quiet standing to dual-tasking in numerous demarcated brain regions correlated with greater dual-task cost (i.e., absolute increase, indicative of worse performance) to postural sway metrics (r = 0.45–0.56, p < 0.01). Lastly, participants who exhibited greater alpha power during dual-tasking in the anterior-right (r = 0.52, p < 0.01) and central-right (r = 0.48, p < 0.01) regions had greater postural sway velocity during dual-tasking.

Conclusion

In healthy older adults, alpha power and theta/beta power ratio change with dual-task standing. The change in theta/beta power ratio in particular may be related to the ability to regulate standing postural control when simultaneously performing unrelated, attention-demanding cognitive tasks. Modulation of brain oscillatory activity might therefore be a novel target to minimize dual-task cost in older adults.

Mobile Brain Imaging to Examine Task-Related Cortical Correlates of Reactive Balance: A Systematic Review

This systematic review examined available findings on spatial and temporal characteristics of cortical activity in response to unpredicted mechanical perturbations. Secondly, this review investigated associations between cortical activity and behavioral/biomechanical measures. Databases were searched from 1980-2021 and a total of 35 cross-sectional studies (31 EEG and 4 fNIRS) were included. Majority of EEG studies assessed perturbation-evoked potentials (PEPs), whereas other studies assessed changes in cortical frequencies. Further, fNIRS studies assessed hemodynamic changes. The PEP-N1, commonly identified at sensorimotor areas, was most examined and was influenced by context prediction, perturbation magnitude, motor adaptation and age. Other PEPs were identified at frontal, parietal and sensorimotor areas and were influenced by task position. Further, changes in cortical frequencies were observed at prefrontal, sensorimotor and parietal areas and were influenced by task difficulty. Lastly, hemodynamic changes were observed at prefrontal and frontal areas and were influenced by task prediction. Limited studies reported associations between cortical and behavioral outcomes. This review provided evidence regarding the involvement of cerebral cortex for sensory processing of unpredicted perturbations, error-detection of expected versus actual postural state, and planning and execution of compensatory stepping responses. There is still limited evidence examining cortical activity during reactive balance tasks in populations with high fall-risk.

Directed network analysis reveals changes in cortical and muscular connectivity caused by different standing balance tasks

Objective.Standing balance forms the basis of daily activities that require the integration of multi-sensory information and coordination of multi-muscle activation. Previous studies have confirmed that the cortex is directly involved in balance control, but little is known about the neural mechanisms of cortical integration and muscle coordination in maintaining standing balance.Approach.We used a direct directed transfer function (dDTF) to analyze the changes in the cortex and muscle connections of healthy subjects (15 subjects: 13 male and 2 female) corresponding to different standing balance tasks.Main results.The results show that the topology of the EEG brain network and muscle network changes significantly as the difficulty of the balancing tasks increases. For muscle networks, the connection analysis shows that the connection of antagonistic muscle pairs plays a major role in the task. For EEG brain networks, graph theory-based analysis shows that the clustering coefficient increases significantly, and the characteristic path length decreases significantly with increasing task difficulty. We also found that cortex-to-muscle connections increased with the difficulty of the task and were significantly stronger than the muscle-to-cortex connections.Significance.These results show that changes in the difficulty of balancing tasks alter EEG brain networks and muscle networks, and an analysis based on the directed network can provide rich information for exploring the neural mechanisms of balance control.

Stabilometric Biofeedback Training in Cognitive and Affective Function Improvement. Contribution of the Russian Scientific School. Part II

This review is the second part of the critical analysis of recent papers of Russian and other authors devoted to the study of the stabilometric parameters in postural control biofeedback training and rehabilitation, associated with psychological functions. The review presents the studies of postural control features in chronic pain syndrome, chronic fatigue syndrome, Parkinson’s disease, multiple sclerosis, and depression. The leading role of Russian researchers in the development and application of stabilometric biofeedback in the training of optimal functioning, rehabilitation, and correction of neurological disorders is noted. The paradigm of stabilometric biofeedback training of the cognitive and affective functions is offered.

Psychophysiological Indicators of Postural Control. Contribution of the Russian Scientific School. Part I

This article aimed to systematically review the published results of studies of psychophysiological mechanisms of posture maintenance and identify the key factors that influence the effectiveness of postural control. The recommendations of "Preferred Reporting Elements for Systematic Reviews and Meta-Analyzes" (PRISMA) were followed for the review. The results were classified, taking into account the target psychophysiological mechanisms and factors affecting postural control. The article presents the theoretical and empirical results of the Russian scientific school of research on the role of support afferentation in the sensorimotor mechanisms of cognitive and postural functions. Due to the limited number of randomized studies found, it was impossible to make meta-analytic comparisons, so the literature analysis was carried out only qualitatively. Meanwhile, our systematic review provides promising information about possible relationships between stabilometric and psychological indicators of postural control, which have theoretical significance and application in the correction and training of posture control. However, more thorough research is needed to overcome the methodological shortcomings that we have encountered in our qualitative analysis.

Assessment of Biomechanical Predictors of Occurrence of Low-Amplitude N1 Potentials Evoked by Naturally Occurring Postural Instabilities

Naturally occurring postural instabilities that occur while standing and walking elicit specific cortical responses in the fronto-central regions (N1 potentials) followed by corrective balance responses to prevent falling. However, no framework could simultaneously track different biomechanical parameters preceding N1s, predict N1s, and assess their predictive power. Here, we propose a framework and show its utility by examining cortical activity (through electroencephalography [EEG]), ground reaction forces, and head acceleration in the anterior-posterior (AP) direction. Ten healthy young adults carried out a balance task of standing on a support surface with or without sway referencing in the AP direction, amplifying, or dampening natural body sway. Using independent components from the fronto-central cortical region obtained from subject-specific head models, we first robustly validated a prior approach on identifying low-amplitude N1 potentials before early signs of balance corrections. Then, a machine learning algorithm was used to evaluate different biomechanical parameters obtained before N1 potentials, to predict the occurrence of N1s. When different biomechanical parameters were directly compared, the time to boundary (TTB) was found to be the best predictor of the occurrence of upcoming low-amplitude N1 potentials during a balance task. Based on these findings, we confirm that the spatio-temporal characteristics of the center of pressure (COP) might serve as an essential parameter that can facilitate the early detection of postural instability in a balance task. Extending our framework to identify such biomarkers in dynamic situations like walking might improve the implementation of corrective balance responses through brain-machine-interfaces to reduce falls in the elderly.

Using kinematics to re-define the pull test as a quantitative biomarker of the postural response in normal pressure hydrocephalus patients

Quantitative biomarkers are needed for the diagnosis, monitoring and therapeutic assessment of postural instability in movement disorder patients. The goal of this study was to create a practical, objective measure of postural instability using kinematic measurements of the pull test. Twenty-one patients with normal pressure hydrocephalus and 20 age-matched control subjects were fitted with inertial measurement units and underwent 10-20 pull tests of varying intensities performed by a trained clinician. Kinematic data were extracted for each pull test and aggregated. Patients participated in 103 sessions for a total of 1555 trials while controls participated in 20 sessions for a total of 299 trials. Patients were separated into groups by MDS-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) pull test score. The center of mass velocity profile easily distinguished between patient groups such that score increases correlated with decreases in peak velocity and later peak velocity onset. All patients except those scored as "3" demonstrated an increase in step length and decrease in reaction time with increasing pull intensity. Groups were distinguished by differences in the relationship of step length to pull intensity (slope) and their overall step length or reaction time regardless of pull intensity (y-intercept). NPH patients scored as "normal" on the MDS-UPDRS scale were kinematically indistinguishable from age-matched control subjects during a standardized perturbation, but could be distinguished from controls by their response to a range of pull intensities. An instrumented, purposefully varied pull test produces kinematic metrics useful for distinguishing clinically meaningful differences within hydrocephalus patients as well as distinguishing these patients from healthy, control subjects.

Cortical Activity During Postural Recovery in Response to Predictable and Unpredictable Perturbations in Healthy Young and Older Adults: A Quantitative EEG Assessment

Introduction:

To investigate the effects of predictable and unpredictable external perturbations on cortical activity in healthy young and older adults.

Methods:

Twenty healthy older and 19 healthy young adults were exposed to predictable and unpredictable external perturbations, and their cortical activity upon postural recovery was measured using a 32-channel quantitative encephalography. The absolute spectral power and coherence z-scores of cortical waves were analyzed through a 3-way mixed ANOVA.

Results:

During postural recovery from predictable perturbations, older adults exhibited higher frontoparietal beta power and higher alpha and beta coherence during the late-phase recovery than the young individuals. After unpredictable perturbations, the older group showed lower alpha power in the early phase and higher beta power in the late phase as compared to the young group. Results for the group × time and group × location interactions in the older group showed a higher alpha and beta coherence over the late phase, a higher alpha coherence in F3–P3 and F4–P4 regions, and a higher beta coherence in the F4–P4 region compared to the younger group.

Conclusion:

Our results revealed that the cortical activation after external perturbations increases with aging, particularly in frontoparietal areas. A shift from automatic (subcortical level) to attentional (cortical level) processing may reflect the contribution of attentional resources for postural recovery from an external threat in older individuals.

Cortical activity, kinematics and trunk muscles activity response to pelvis movements during unstable sitting

BACKGROUND

Balance control is a leading component of human motor activities and its impairment is associated with an increased risk of falling, lower back pain due to impaired motor control mechanism. Prolonged sitting position at workplace is one of the risk factors of reduced postural control and lower back pain.

OBJECTIVE

To evaluate theta and alpha waves cortical activity, trunk muscles activity and kinematics in static sitting, dynamic sitting on different platforms: simple wobble board (WB) and wobble board on bearing surface (WBB).

METHODS

The kinematics of body segments, electromyography of five trunk muscles, electroencephalography of 32 scalp electrodes were measured during balance tasks in sitting position for 17 subjects with continuous seated position at workplace.

RESULTS

Cortical power on WBB1 increase in fronto - central (p< 0.05) region while on WBB2 increase in centro - parietal region (p< 0.05). WBB2 increase more muscles compared with WB2. The amplitude of movement of ASIS, Th10 can be seen lower on WBB compared with WB (p< 0.05).

CONCLUSIONS

The study shows that WBB can increase personalized sitting and improve trunk motor control during hours of prolonged sitting.

EFFECT OF LOWER LIMB EXERCISE ON POSTURE STABILITY AND BRAIN ACTIVITY DURING WHOLE BODY VIBRATION FOR THE ELDERLY

This study aimed to investigate the effect of lower limb exercise on electroencephalogram (EEG) activity and posture stability during whole body vibration (WBV) for healthy elderly people. Subjects were composed of 20 elderly people who were over 60 years old and had no disease. They were subjected to WBV of 30[Formula: see text]Hz and strength intensity of 20 (total 5 sets, 20[Formula: see text]s/set, rest time: 20[Formula: see text]s, except for the final set). The subjects were grouped into two groups. One group of 11 subjects was WBVSt (WBV of upright stance) and the other group of nine subjects was WBVSq (WBV of squat posture). In the WBVSt group, the subjects were requested to maintain a standing position, whereas those in the WBVSq group were asked to perform 60∘-knee flexion squat at 2[Formula: see text]s intervals during WBV stimulation. In this study, the electromyography (EMG) was measured on the right and left erector spinae, rectus femoris, vastus lateralis, vastus medialis, tibialis anterior to evaluate lower limb muscle activity and postural stability during timed up and go (TUG) test before and after WBV. The EEG was measured on frontal (F3, F4, F7, F8), central (Cz, C3, C4), temporal (T3, T4, T5, T6), parietal (P3, P4), and occipital (O1, O2) lobes to evaluate brain activity during the check of mini-mental state examination for dementia screening (MMSE-DS) before and after WBV. The results of this study showed improved postural stability and muscle activation for the healthy elderly during lower limb and WVB exercises. The WBVSq group showed higher changes in TUG-test ([Formula: see text]) and iEMG analysis by EMG ([Formula: see text]) compared with the WBVSt group. However, there was no significant change in MMSE-DS ([Formula: see text]). Because of the increase in relative SMR power by EEG, the central (C4), frontal (F7) and parietal (P3, P4) lobes were activated in WBVSt group ([Formula: see text]); however, all regions, except the parietal lobe, were activated in WBVSq group ([Formula: see text]). Lower limb exercise with WBV stimulation improved postural stability, lower limb muscle, and brain activation for the elderly. These results may be helpful to the protocol of exercise using WBV for the healthy elderly.

Cortical correlates in upright dynamic and static balance in the elderly

Falls are the second most frequent cause of injury in the elderly. Physiological processes associated with aging affect the elderly's ability to respond to unexpected balance perturbations, leading to increased fall risk. Every year, approximately 30% of adults, 65 years and older, experiences at least one fall. Investigating the neurophysiological mechanisms underlying the control of static and dynamic balance in the elderly is an emerging research area. The study aimed to identify cortical and muscular correlates during static and dynamic balance tests in a cohort of young and old healthy adults. We recorded cortical and muscular activity in nine elderly and eight younger healthy participants during an upright stance task in static and dynamic (core board) conditions. To simulate real-life dual-task postural control conditions, the second set of experiments incorporated an oddball visual task. We observed higher electroencephalographic (EEG) delta rhythm over the anterior cortex in the elderly and more diffused fast rhythms (i.e., alpha, beta, gamma) in younger participants during the static balance tests. When adding a visual oddball, the elderly displayed an increase in theta activation over the sensorimotor and occipital cortices. During the dynamic balance tests, the elderly showed the recruitment of sensorimotor areas and increased muscle activity level, suggesting a preferential motor strategy for postural control. This strategy was even more prominent during the oddball task. Younger participants showed reduced cortical and muscular activity compared to the elderly, with the noteworthy difference of a preferential activation of occipital areas that increased during the oddball task. These results support the hypothesis that different strategies are used by the elderly compared to younger adults during postural tasks, particularly when postural and cognitive tasks are combined. The knowledge gained in this study could inform the development of age-specific rehabilitative and assistive interventions.

Gamma-Band Frequency Analysis and Motor Development in Music-Trained Children: A Cross-Sectional Study

Background: The aim of this study was to analyze the gamma-band frequency and motor performance of children with and without music training.Methods: This cross-sectional study included 31 right-handed children, 6-11 years old, who were allocated to two groups: 1) the music group (MG), including children who attended preschool and musical training (n = 16), and 2) the no-music group (NMG), including children who attended preschool but received no additional music training (n = 15). The outcomes were gamma-band frequency measured by electroencephalography, manual dexterity, aim-and-catch, and static and dynamic balance abilities measured by the Movement Assessment Battery for Children, and fine motor skills, overall motor skills, balance, corporal body scheme, spatial organization, temporal orientation, and general motor quotient (GMQ) by a Brazilian scale for motor development.Results: There 1was a significant difference between groups in the peak frequency (p = 0.0195) and median frequency (p = 0.0070) in the F3-F4 regions. Static and dynamic balance (p = 0.03), temporal orientation (p < 0.01), and GMQ (p < 0.03) were higher in MG than in NMG.Conclusion: The musically trained children had increased gamma-peak frequency in the frontal region and greater temporal orientation, balance, and the overall motor quotient.

Oscillatory Activity in Mouse Lemur Primary Motor Cortex During Natural Locomotor Behavior

In arboreal environments, substrate orientation determines the biomechanical strategy for postural maintenance and locomotion. In this study, we investigated possible neuronal correlates of these mechanisms in an ancestral primate model, the gray mouse lemur. We conducted telemetric recordings of electrocorticographic activity in left primary motor cortex of two mouse lemurs moving on a branch-like small-diameter pole, fixed horizontally, or vertically. Analysis of cortical oscillations in high β (25–35 Hz) and low γ (35–50 Hz) bands showed stronger resting power on horizontal than vertical substrate, potentially illustrating sensorimotor processes for postural maintenance. Locomotion on horizontal substrate was associated with stronger event-related desynchronization than vertical substrate, which could relate to locomotor adjustments and/or derive from differences in baseline activity. Spectrograms of cortical activity showed modulation throughout individual locomotor cycles, with higher values in the first than second half cycle. However, substrate orientation did not significantly influence these variations. Overall, these results confirm that specific cortical mechanisms are solicited during arboreal locomotion, whereby mouse lemurs adjust cortical activity to substrate orientation during static posture and locomotion, and modulate this activity throughout locomotor cycles.

Long-Lasting Event-Related Beta Synchronizations of Electroencephalographic Activity in Response to Support-Surface Perturbations During Upright Stance: A Pilot Study Associating Beta Rebound and Active Monitoring in the Intermittent Postural Control

Movement related beta band cortical oscillations, including beta rebound after execution and/or suppression of movement, have drawn attention in upper extremity motor control literature. However, fewer studies focused on beta band oscillations during postural control in upright stance. In this preliminary study, we examined beta rebound and other components of electroencephalogram (EEG) activity during perturbed upright stance to investigate supraspinal contributions to postural stabilization. Particularly, we aimed to clarify the timing and duration of beta rebound within a non-sustained, but long-lasting postural recovery process that occurs more slowly compared to upper extremities. To this end, EEG signals were acquired from nine healthy young adults in response to a brief support-surface perturbation, together with the center of pressure, the center of mass and electromyogram (EMG) activities of ankle muscles. Event-related potentials (ERPs) and event-related spectral perturbations were computed from EEG data using the perturbation-onset as a triggering event. After short-latency (<0.3 s) ERPs, our results showed a decrease in high-beta band oscillations (event-related desynchronization), which was followed by a significant increase (event-related synchronization) in the same band, as well as a decrease in theta band oscillations. Unlike during upper extremity motor tasks, the beta rebound in this case was initiated before the postural recovery was completed, and sustained for as long as 3 s with small EMG responses for the first half period, followed by no excessive EMG activities for the second half period. We speculate that those novel characteristics of beta rebound might be caused by slow postural dynamics along a stable manifold of the unstable saddle-type upright equilibrium of the postural control system without active feedback control, but with active monitoring of the postural state, in the framework of the intermittent control.

Learned Overweight Internal Model Can Be Activated to Maintain Equilibrium When Tactile Cues Are Uncertain: Evidence From Cortical and Behavioral Approaches

Human adaptive behavior in sensorimotor control is aimed to increase the confidence in feedforward mechanisms when sensory afferents are uncertain. It is thought that these feedforward mechanisms rely on predictions from internal models. We investigate whether the brain uses an internal model of physical laws (gravitational and inertial forces) to help estimate body equilibrium when tactile inputs from the foot sole are depressed by carrying extra weight. As direct experimental evidence for such a model is limited, we used Judoka athletes thought to have built up internal models of external loads (i.e., opponent weight management) as compared with Non-Athlete participants and Dancers (highly skilled in balance control). Using electroencephalography, we first (experiment 1) tested the hypothesis that the influence of tactile inputs was amplified by descending cortical efferent signals. We compared the amplitude of P1N1 somatosensory cortical potential evoked by electrical stimulation of the foot sole in participants standing still with their eyes closed. We showed smaller P1N1 amplitudes in the Load compared to No Load conditions in both Non-Athletes and Dancers. This decrease neural response to tactile stimulation was associated with greater postural oscillations. By contrast in the Judoka's group, the neural early response to tactile stimulation was unregulated in the Load condition. This suggests that the brain can selectively increase the functional gain of sensory inputs, during challenging equilibrium tasks when tactile inputs were mechanically depressed by wearing a weighted vest. In Judokas, the activation of regions such as the right posterior inferior parietal cortex (PPC) as early as the P1N1 is likely the source of the neural responses being maintained similar in both Load and No Load conditions. An overweight internal model stored in the right PPC known to be involved in maintaining a coherent representation of one's body in space can optimize predictive mechanisms in situations with high balance constraints (Experiment 2). This hypothesis has been confirmed by showing that postural reaction evoked by a translation of the support surface on which participants were standing wearing extra-weight was improved in Judokas.

Muscular and cortical activation during dynamic and static balance in the elderly: A scoping review

Falls due to balance impairment are a major cause of injury and disability in the elderly. The study of neurophysiological correlates during static and dynamic balance tasks is an emerging area of research that could lead to novel rehabilitation strategies and reduce fall risk. This review aims to highlight key concepts and identify gaps in the current knowledge of balance control in the elderly that could be addressed by relying on surface electromyographic (EMG) and electroencephalographic (EEG) recordings. The neurophysiological hypotheses underlying balance studies in the elderly as well as the methodologies, findings, and limitations of prior work are herein addressed. The literature shows: 1) a wide heterogeneity in the experimental procedures, protocols, and analyses; 2) a paucity of studies involving the investigation of cortical activity; 3) aging-related alterations of cortical activation during balance tasks characterized by lower cortico-muscular coherence and increased allocation of attentional control to postural tasks in the elderly; and 4) EMG patterns characterized by delayed onset after perturbations, increased levels of activity, and greater levels of muscle co-activation in the elderly compared to younger adults. EMG and EEG recordings are valuable tools to monitor muscular and cortical activity during the performance of balance tasks. However, standardized protocols and analysis techniques should be agreed upon and shared by the scientific community to provide reliable and reproducible results. This will allow researchers to gain a comprehensive knowledge on the neurophysiological changes affecting static and dynamic balance in the elderly and will inform the design of rehabilitative and preventive interventions.

Effects of exergames training on postural balance in patients who had a chronic stroke: study protocol for a randomised controlled trial

INTRODUCTION

Exergames training, as an additional therapy to standard care, has been widely used for motor recovery after patients who had a stroke, and it is a valuable and positive tool in the rehabilitation of this population. This study describes a single-blind randomised clinical trial that will aim to investigate the effects of exergames training on postural balance in patients with chronic stroke.

METHODS AND ANALYSIS

Forty-two individuals with chronic stroke (>6 months), aged 20-75 years, will be randomised into two groups: the experimental group, which will be subjected to an exergames protocol, and control group, which will undergo a kinesiotherapy protocol. Both protocols are based on postural balance. The intervention will consist of 40-minute sessions two times per week for 10 consecutive weeks. The volunteers will be evaluated before the treatment, at the end of the interventions and 8 weeks thereafter. The primary outcome will be postural balance (Berg Balance Scale, Functional Reach Test, Timed Up and Go test and Centre of Pressure variables) and secondary outcomes will include gait (6 m timed walk and Kinovea Software), cortical activation patterns (electroencephalography Emotiv EPOC), functional independence (Functional Independence Measure), quality of life (Stroke-Specific Quality of Life Scale) and motivation (Intrinsic Motivation Inventory).

ETHICS AND DISSEMINATION

This protocol was approved by the Ethics Committee of the Federal University of Rio Grande do Norte (number 3.434.350). The results of the study will be disseminated to participants through social networks and will be submitted to a peer-reviewed journal and scientific meetings.

TRIAL REGISTRATION NUMBER

Brazilian Registry of Clinical Trials (RBR-78v9hx).

Aging-related changes in cortical mechanisms supporting postural control during base of support and optic flow manipulations

Behavioral findings suggest that aging alters the involvement of cortical sensorimotor mechanisms in postural control. However, corresponding accounts of the underlying neural mechanisms remain sparse, especially the extent to which these mechanisms are affected during more demanding tasks. Here, we set out to elucidate cortical correlates of altered postural stability in younger and older adults. 3D body motion tracking and high-density electroencephalography (EEG) were measured while 14 young adults (mean age = 24 years, 43% women) and 14 older adults (mean age = 77 years, 50% women) performed a continuous balance task under four different conditions. Manipulations were applied to the base of support (either regular or tandem (heel-to-toe) stance) and visual input (either static visual field or dynamic optic flow). Standing in tandem, the more challenging position, resulted in increased sway for both age groups, but for the older adults, only this effect was exacerbated when combined with optic flow compared to the static visual display. These changes in stability were accompanied by neuro-oscillatory modulations localized to midfrontal and parietal regions. A cluster of electro-cortical sources localized to the supplementary motor area showed a large increase in theta spectral power (4-7 Hz) during tandem stance, and this modulation was much more pronounced for the younger group. Additionally, the older group displayed widespread mu (8-12 Hz) and beta (13-30 Hz) suppression as balance tasks placed more demands on postural control, especially during tandem stance. These findings may have substantial utility in identifying early cortical correlates of balance impairments in otherwise healthy older adults.

Decreased Theta Power Reflects Disruption in Postural Control Networks of Fragile X Premutation Carriers. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2020;2020:2845-2848. [PMID: 33018599 DOI: 10.1109/embc44109.2020.9176289] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

FRM1 premutation carriers exhibit various subtle deficits in balance and stability, prior to the development of the movement disorder Fragile X Associated Tremor/Ataxia Syndrome (FXTAS). Force plate posturography has increasingly been combined with the temporal sensitive imaging methods such as EEG to offer insight into the neural mechanisms which govern postural control. This study investigated cortical theta power during continuous balance and its relationship to balance performance in Fragile X premutation carriers. Eight premutation carriers and 6 controls stood on a force platform under altered sensory and cognitive conditions while postural sway and high-density EEG data were simultaneously recorded. Carriers exhibited greater sway area when sensory input was reduced (p=0.01) and cognitive load was increased (p=0.01), as well as significantly reduced frontal theta power compared to the Control Group. The relationship between theta power and postural control seen in the control group may indicate an increase in error detection caused by reduced visual input and greater discrepancies between expected and actual balance state. While the lower theta power in frontal regions of carriers may indicate a disruption in neural networks underpinning postural control. Such results provide new insight into the neural correlates of balance control in Fragile X premutation carriers.

Increased EEG alpha peak frequency in adolescents with idiopathic scoliosis during balance control in normal upright standing

Adolescent idiopathic scoliosis (AIS) is a multifactorial disorder characterized by a tridimensional deformation of the spine. AIS pathophysiology is still unclear and its aetiology is unknown. Results from several studies revealed balance control alterations in adolescents with AIS suggesting cortical sensorimotor processing impairments. Studies assessing cortical activity involved in balance control revealed an increase in alpha peak frequency (APF), which is a neurophysiological marker of thalamo-cortical transmission, related to a more challenging balance task. The objective of this study is to assess APF of adolescents with AIS during balance control in upright standing posture using electroencephalography (EEG). EEG was recorded in 16 girls with AIS and 15 control girls in normal standing posture on a force platform. The participants stood upright for 2 min with eyes open and 2 min with eyes closed. Fast Fourier transformations of EEG data were calculated to obtain APF. Balance performances were assessed through the area of an ellipse covering the center of pressure (COP) displacement and the root mean square value of the COP velocity. Compared to the control group, APF was higher in the AIS group at central, frontal, parietal and occipital regions. Further, COP analyses did not reveal any difference between AIS and control groups. A higher APF may indicate the need for increased cortical processing to maintain balance control in normal upright standing in adolescents with AIS compared to healthy controls. We suggest that this may be a compensatory strategy to overcome balance control challenges.

Modulations of Inter-Hemispherical Phase Coupling in Human Single Leg Stance

INTRODUCTION

Recent findings from neuroimaging studies provided initial insights into cortical contributions to postural control. These studies observed enhanced cortical activation and connectivity when task-difficulty and postural instability increased. However, little attention has been paid to the allocation of cortical networks appearing with a decreasing base of support from bipedal to single leg stance. Therefore, the aim of the present study was to investigate modulations of functional connectivity from bipedal to single leg stance.

EXPERIMENTAL PROCEDURES

Cortical activity during bipedal and single leg stance (left) was investigated in 15 male subjects using 128 channel mobile electroencephalography (EEG), while standing on a triaxial force plate. Power spectral density was calculated for theta (4-7 Hz), alpha-1 (8-10 Hz) and alpha-2 (10-12 Hz) frequency bands. Estimations of the phase lag index (PLI) were conducted as a measure of functional connectivity. Moreover, postural control was analyzed by the area of sway and sway velocity.

RESULTS

The results demonstrated a significantly increased area of sway and decreased alpha-2 power in single leg compared to bipedal stance. Furthermore, PLIs within the alpha-2 frequency band showed significantly decreased inter-hemispherical phase coupling in single leg stance, associated with connections involving the left motor region.

DISCUSSION

Altogether, the present findings may indicate modulations of cortical contributions in single leg compared to bipedal stance. The present data suggest that decreased inter-hemispherical functional connectivity, in conjunction with a global increase in cortical excitability, may indicate enhanced alertness and task-specific selective inhibition of motor networks in favor of postural control.

Investigating prismatic adaptation effects in handgrip strength and in plantar pressure in healthy subjects

BACKGROUND

Prismatic Adaptation (PA) is a visuomotor procedure inducing a shift of the visual field that has been shown to modulate activation of a number of brain areas, in posterior (i.e. parietal cortex) and anterior regions (i.e. frontal cortex). This neuromodulation could be useful to study neural mechanisms associated with either postural measures such as the distribution of plantar pressure or to the generation of muscle strength. Indeed, plantar pressure distribution is associated to activation of high-level cognitive mechanisms taking place within the posterior regions of the brain dorsal stream, especially of the right hemisphere. Conversely, hand force mostly rely on sensorimotor mechanisms, fulfilled by anterior regions of the brain and involving both hemispheres.

RESEARCH QUESTION

Since PA effects have been reported to affect both sensorimotor and higher level cognitive processes, is it possible to hypothesize a modulation of both hands strenght and plantar pressure after PA?

METHODS

Forty-six healthy subjects (male = 23; mean age = 25 ± 3 years) were randomly divided into two groups: a leftward prismatic adaptation group (l-PA) and a rightward prismatic adaptation group (r-PA). Hand strength and plantar pressure were assessed, immediately before and after PA, using the handgrip task and baropodometric measurement, respectively.

RESULTS

Both l-PA and r-PA induced a significant decrease of strength in the hand contralateral to the lenses deviation side. Only r-PA was associated with an increase of the forefoot plantar pressure in both feet. Modulation of interhemispheric inhibitory processes at sensorimotor and higher cognitive level may account for the present results.

SIGNIFICANCE

PA exerts effects on body posture and hand strength relying on different mechanisms. The PA effects on hand strength are probably related to the modulation of interhemispheric inhibition of sensorimotor processes, involving both hemispheres. The PA effects on body posture are probably related to modulation of body representation, involving mainly the right hemisphere.

Cortical Theta Activity and Postural Control in Non-Visual and High Cognitive Load Tasks: Impact for Clinical Studies

Due to the major role of balance in our everyday lives and the unsatisfying understanding of the role of neural mechanism on balance control, the focus of this study was to explore the role of the cerebral cortex and its effects on stability. We investigated the effects of non-visual and cognitive tasks on balance performance and cortical theta response in a small, convenient sample. The cognitive tasks were N-back and Sustained Attention Response Task (SART). Cortical theta activity showed strong correlations with balance performance metrics. Particularly, central regions showed an increase in theta power in more cognitively challenging tasks but not statistically significant. Parietal theta power had a statistically significant increase in tasks that led to a heavier reliance on proprioception and vestibular information. This study shows the efficacy of EEG recording during balance control tasks. Future studies on neurodegenerative diseases that affect neuromotor control could investigate these outcomes.

Brain activity during dual task gait and balance in aging and age-related neurodegenerative conditions: A systematic review

The aims of this systematic review were to investigate (1) real-time brain activity during DT gait and balance, (2) whether changes in brain activity correlate with changes in behavioral outcomes in older adults and people with age-related neurodegenerative conditions. PubMed, PsycINFO, and Web of Science were searched from 2009 to 2019 using the keywords dual task, brain activity, gait, balance, aging, neurodegeneration, and other related search terms. A total of 15 articles were included in this review. Functional near-infrared spectroscopy and electroencephalogram measures demonstrated that older adults had higher brain activity, particularly in the prefrontal cortex (PFC), compared to young adults during dual task gait and balance. Similar neurophysiological results were observed in people with age-related neurodegenerative conditions. Few studies demonstrated a relationship between increased brain activity and better behavioral outcomes. This systematic review supports the notion that aging and age-related neurodegenerative conditions are associated with neuronal network changes, resulting in increased brain activity specifically in the PFC. Further studies are warranted to assess the relationship between increased PFC activation during dual task gait and balance and behavioral outcomes to better optimize the rehabilitation interventions.

[Dual-tasks is an indicator of cognitive deficit specificity in patients after traumatic brain injury]

AIM

To investigate the brain activity impairment in patients after traumatic brain injury (TBI) during dual-tasks in comparison with the normal ranges.

MATERIAL AND METHODS

Electroencephalographic (EEG), stabilographic and clinical study was performed in 9 patients (mean age 25±1.2 years) for up to 3 months after a mild traumatic brain injury (TBI) in comparison with 18 healthy subjects (mean age 26.6±0.07 years). All participants of the study performed two motor tasks and two cognitive tasks that were carried out in isolation, and simultaneously (dual-tasks).

RESULTS

Clinical examination revealed cognitive deficit in TBI patients with safety of postural control. The EEG data demonstrated a pronounced decrease in the coherence for slow rhythms in the left hemisphere and frontal areas during cognitive tasks performance. In healthy subjects, an increase in EEG coherence for slow spectral bands was observed in these brain areas.

CONCLUSION

Dual-tasks are an informative method for estimation of predominant cognitive deficit after mild TBI and the use of this approach for rehabilitation contributes to positive clinical dynamics.

Cortical recruitment and functional dynamics in postural control adaptation and habituation during vibratory proprioceptive stimulation

OBJECTIVE

Maintaining upright posture is a complex task governed by the integration of afferent sensorimotor and visual information with compensatory neuromuscular reactions. The objective of the present work was to characterize the visual dependency and functional dynamics of cortical activation during postural control.

APPROACH

Proprioceptic vibratory stimulation of calf muscles at 85 Hz was performed to evoke postural perturbation in open-eye (OE) and closed-eye (CE) experimental trials, with pseudorandom binary stimulation phases divided into four segments of 16 stimuli. 64-channel EEG was recorded at 512 Hz, with perturbation epochs defined using bipolar electrodes placed proximal to each vibrator. Power spectra variation and linearity analysis was performed via fast Fourier transformation into six frequency bands (Δ, 0.5-3.5 Hz; θ, 3.5-7.5 Hz; α, 7.5-12.5 Hz; β, 12.5-30 Hz; [Formula: see text], 30-50 Hz; and [Formula: see text], 50-80 Hz). Finally, functional connectivity assessment was explored via network segregation and integration analyses.

MAIN RESULTS

Spectra variation showed waveform and vision-dependent activation within cortical regions specific to both postural adaptation and habituation. Generalized spectral variation yielded significant shifts from low to high frequencies in CE adaptation trials, with overall activity suppressed in habituation; OE trials showed the opposite phenomenon, with both adaptation and habituation yielding increases in spectral power. Finally, our analysis of functional dynamics reveals novel cortical networks implicated in postural control using EEG source-space brain networks. In particular, our reported significant increase in local θ connectivity may signify the planning of corrective steps and/or the analysis of falling consequences, while α band network integration results reflect an inhibition of error detection within the cingulate cortex, likely due to habituation.

SIGNIFICANCE

Our findings principally suggest that specific cortical waveforms are dependent upon the availability of visual feedback, and we furthermore present the first evidence that local and global brain networks undergo characteristic modification during postural control.

Exergames Inherently Contain Cognitive Elements as Indicated by Cortical Processing

Exergames are increasingly used to train both physical and cognitive functioning, but direct evidence whether and how exergames affect cortical activity is lacking. Although portable electroencephalography (EEG) can be used while exergaming, it is unknown whether brain activity will be obscured by movement artifacts. The aims of this study were to assess whether electrophysiological measurements during exergaming are feasible and if so, whether cortical activity changes with additional cognitive elements. Twenty-four young adults performed self-paced sideways leaning movements, followed by two blocks of exergaming in which participants completed a puzzle by leaning left or right to select the correct piece. At the easy level, only the correct piece was shown, while two pieces were presented at the choice level. Brain activity was recorded using a 64-channel passive EEG system. After filtering, an adaptive mixture independent component analysis identified the spatio-temporal sources of brain activity. Results showed that it is feasible to record brain activity in young adults while playing exergames. Furthermore, five spatially different clusters were identified located frontal, bilateral central, and bilateral parietal. The frontal cluster had significantly higher theta power in the exergaming condition with choice compared to self-paced leaning movements and exergaming without choice, while both central clusters showed a significant increase in absolute alpha-2 power in the exergaming conditions compared to the self-paced movements. This is the first study to show that it is feasible to record brain activity while exergaming. Furthermore, results indicated that even a simple exergame without explicit cognitive demands inherently requires cognitive processing. These results pave the way for studying brain activity during various exergames in different populations to help improve their effective use in rehabilitation settings.

Ankle sprain as a work-related accident: status of proprioception after 2 weeks

Purpose

This study aims at verifying whether proprioception is abnormal or not, two weeks after a grade 1 and 2 ankle sprain in the scope of work-related accident.

Methods

A descriptive, observation and transversal study was designed to compare speed, movement and oscilation of centre of pressure in employees of companies signed up to a mutual company. Participants’ healthy feet comprised the control group, and feet that had undergone an ankle sprain due to a work-related accident comprised the cases group. The following stability tests were undertaken to both the healthy and injuried feet using a force plate: Monopodal Romberg test with eyes open, Monopodal Romberg test with eyes open on a 30 mm thick foam rubber, Monopodal Romberg test with eyes closed, and Romberg test as monopodal support with eyes closed on a 30 mm thick foam rubber. A multiple logistic regression analysis was performed. From the results of this regression model the COR curve test was performed.

Results

71.7% accuracy in the predictions was attained. The equation was as follows: Condition (injured or healthy) = 0.052⋅% RGC AP Movement − 0.81⋅MREO AP Movement. The variable MREO antero-posterior movement was used in the COR curve methodology. The area under the curve was greater than 0.65 and at a 95% confidence interval the 0.75 value was included, which in our case was the injured subject condition. Values for sensitivity, specificity, positive predictive value and negative predictive value were 0.667, 0.633, 64.5%, and 65.5%, respectively.

Conclusion

The participants in this study showed a diminished capacity for postural control in an ankle two weeks after an ankle sprain.

Neurofeedback-induced facilitation of the supplementary motor area affects postural stability

Near-infrared spectroscopy-mediated neurofeedback (NIRS-NFB) is a promising therapeutic intervention for patients with neurological diseases. Studies have shown that NIRS-NFB can facilitate task-related cortical activation and induce task-specific behavioral changes. These findings indicate that the effect of neuromodulation depends on local cortical function. However, when the target cortical region has multiple functions, our understanding of the effects is less clear. This is true in the supplementary motor area (SMA), which is involved both in postural control and upper-limb movement. To address this issue, we investigated the facilitatory effect of NIRS SMA neurofeedback on cortical activity and behavior, without any specific task. Twenty healthy individuals participated in real and sham neurofeedback. Balance and hand dexterity were assessed before and after each NIRS-NFB session. We found a significant interaction between assessment periods (pre/post) and condition (real/sham) with respect to balance as assessed by the center of the pressure path length but not for hand dexterity as assessed by the 9-hole peg test. SMA activity only increased during real neurofeedback. Our findings indicate that NIRS-NFB itself has the potential to modulate focal cortical activation, and we suggest that it be considered a therapy to facilitate the SMA for patients with postural impairment.

Visual transparent & visual occlusion: An EEG and COP study

Electroencephalography (EEG) and centre of pressure (COP) data were recorded in young adults for 60 seconds during standing in visual transparent (VT) and visual occlusion (VO) conditions. In both of these conditions, participants wore VO liquid crystal spectacles which allowed the experimenter to accurately control visual information being presented or occluded to the participant. Alpha band (8-13 Hz) revealed significant differences in channel-averaged power spectrum in these two conditions, but not theta band (4-8 Hz) and beta band (13-30 Hz). In order to determine which channels contributed to these bands, region-averaged and single-channel power spectrum were computed which revealed similar patterns for eyes-open (VT) and eyes-closed (VO) conditions in each band. COP analysis was performed to understand postural steadiness in VT and VO conditions; the analysis indicated significant and larger time-domain distance measures (mean velocity), time-domain hybrid measures (mean frequency and sway area) and frequency domain measures (centroidal frequency) in the VO condition. The increased of alpha power in most frontal and posterior regions was indicative of the cortical processing of vision.

Motor learning in a complex balance task and associated neuroplasticity: a comparison between endurance athletes and nonathletes

Studies suggested that motor expertise is associated with functional and structural brain alterations, which positively affect sensorimotor performance and learning capabilities. The purpose of the present study was to unravel differences in motor skill learning and associated functional neuroplasticity between endurance athletes (EA) and nonathletes (NA). For this purpose, participants had to perform a multimodal balance task (MBT) training on 2 sessions, which were separated by 1 wk. Before and after MBT training, a static balance task (SBT) had to be performed. MBT-induced functional neuroplasticity and neuromuscular alterations were assessed by means of functional near-infrared spectroscopy (fNIRS) and electromyography (EMG) during SBT performance. We hypothesized that EA would showed superior initial SBT performance and stronger MBT-induced improvements in SBT learning rates compared with NA. On a cortical level, we hypothesized that MBT training would lead to differential learning-dependent functional changes in motor-related brain regions [such as primary motor cortex (M1)] during SBT performance. In fact, EA showed superior initial SBT performance, whereas learning rates did not differ between groups. On a cortical level, fNIRS recordings (time × group interaction) revealed a stronger MBT-induced decrease in left M1 and inferior parietal lobe (IPL) for deoxygenated hemoglobin in EA. Even more interesting, learning rates were correlated with fNIRS changes in right M1/IPL. On the basis of these findings, we provide novel evidence for superior MBT training-induced functional neuroplasticity in highly trained athletes. Future studies should investigate these effects in different sports disciplines to strengthen previous work on experience-dependent neuroplasticity.NEW & NOTEWORTHY Motor expertise is associated with functional/structural brain plasticity. How such neuroplastic reorganization translates into altered motor learning processes remains elusive. We investigated endurance athletes (EA) and nonathletes (NA) in a multimodal balance task (MBT). EA showed superior static balance performance (SBT), whereas MBT-induced SBT improvements did not differ between groups. Functional near-infrared spectroscopy recordings revealed a differential MBT training-induced decrease of deoxygenated hemoglobin in left primary motor cortex and inferior parietal lobe between groups.

Cerebral Dynamics during the Observation of Point-Light Displays Depicting Postural Adjustments

Objective: As highly social creatures, human beings rely part of their skills of identifying, interpreting, and predicting the actions of others on the ability of perceiving biological motion. In the present study, we aim to investigate the electroencephalographic (EEG) cerebral dynamics involved in the coding of postural control and examine whether upright stance would be codified through the activation of the temporal-parietal cortical network classically enrolled in the coding of biological motion. Design: We registered the EEG activity of 12 volunteers while they passively watched point light displays (PLD) depicting quiet stable (QB) and an unstable (UB) postural situations and their respective scrambled controls (QS and US). In a pretest, 13 volunteers evaluated the level of stability of our two biological stimuli through a stability scale. Results: Contrasting QB vs. QS revealed a typical ERP difference in the right temporal-parietal region at an early 200-300 ms time window. Furthermore, when contrasting the two biological postural conditions, UB vs. QB, we found a higher positivity in the 400-600 ms time window for the UB condition in central-parietal electrodes, lateralized to the right hemisphere. Conclusions: These results suggest that PLDs depicting postural adjustments are coded in the brain as biological motion, and that their viewing recruit similar networks with those engaged in postural stability control. Additionally, higher order cognitive processes appear to be engaged in the identification of the postural instability level. Disentangling the EEG dynamics during the observation of postural adjustments could be very useful for further understanding the neural mechanisms underlying postural control.

Neuroimaging of Human Balance Control: A Systematic Review

This review examined 83 articles using neuroimaging modalities to investigate the neural correlates underlying static and dynamic human balance control, with aims to support future mobile neuroimaging research in the balance control domain. Furthermore, this review analyzed the mobility of the neuroimaging hardware and research paradigms as well as the analytical methodology to identify and remove movement artifact in the acquired brain signal. We found that the majority of static balance control tasks utilized mechanical perturbations to invoke feet-in-place responses (27 out of 38 studies), while cognitive dual-task conditions were commonly used to challenge balance in dynamic balance control tasks (20 out of 32 studies). While frequency analysis and event related potential characteristics supported enhanced brain activation during static balance control, that in dynamic balance control studies was supported by spatial and frequency analysis. Twenty-three of the 50 studies utilizing EEG utilized independent component analysis to remove movement artifacts from the acquired brain signals. Lastly, only eight studies used truly mobile neuroimaging hardware systems. This review provides evidence to support an increase in brain activation in balance control tasks, regardless of mechanical, cognitive, or sensory challenges. Furthermore, the current body of literature demonstrates the use of advanced signal processing methodologies to analyze brain activity during movement. However, the static nature of neuroimaging hardware and conventional balance control paradigms prevent full mobility and limit our knowledge of neural mechanisms underlying balance control.

Body sway adaptation to addition but not withdrawal of stabilizing visual information is delayed by a concurrent cognitive task

The aim of this study was to test the effects of a concurrent cognitive task on the promptness of the sensorimotor integration and reweighting processes following addition and withdrawal of vision. Fourteen subjects stood in tandem while vision was passively added and removed. Subjects performed a cognitive task, consisting of counting backward in steps of three, or were "mentally idle." We estimated the time intervals following addition and withdrawal of vision at which body sway began to change. We also estimated the time constant of the exponential change in body oscillation until the new level of sway was reached, consistent with the current visual state. Under the mentally idle condition, mean latency was 0.67 and 0.46 s and the mean time constant was 1.27 and 0.59 s for vision addition and withdrawal, respectively. Following addition of vision, counting backward delayed the latency by about 300 ms, without affecting the time constant. Following withdrawal, counting backward had no significant effect on either latency or time constant. The extension by counting backward of the time interval to stabilization onset on addition of vision suggests a competition for allocation of cortical resources. Conversely, the absence of cognitive task effect on the rapid onset of destabilization on vision withdrawal, and on the relevant reweighting time course, advocates the intervention of a subcortical process. Diverting attention from a challenging standing task discloses a cortical supervision on the process of sensorimotor integration of new balance-stabilizing information. A subcortical process would instead organize the response to removal of the stabilizing sensory input.NEW & NOTEWORTHY This study is the first to test the effect of an arithmetic task on the time course of balance readjustment following visual withdrawal or addition. Performing such a cognitive task increases the time delay following addition of vision but has no effect on withdrawal dynamics. This suggests that sensorimotor integration following addition of a stabilizing signal is performed at a cortical level, whereas the response to its withdrawal is "automatic" and accomplished at a subcortical level.