Using virtual reality to induce multi-trial inattentional blindness despite trial-by-trial measures of awareness.

Unconscious processing has been widely examined using diverse and well-controlled methodologies. However, the extent to which these findings are relevant to real-life instances of information processing without awareness is limited. Here, we present a novel inattentional blindness (IB) paradigm in virtual reality (VR). In three experiments, we managed to repeatedly induce IB while participants foveally viewed salient stimuli for prolonged durations. The effectiveness of this paradigm demonstrates the close relationship between top-down attention and subjective experience. Thus, this method provides an ecologically valid setup to examine processing without awareness.

Dopamine improves defective cortical and muscular connectivity during bilateral control of gait in Parkinson's disease.

Parkinson's Disease (PD)-typical declines in gait coordination are possibly explained by weakness in bilateral cortical and muscular connectivity. Here, we seek to determine whether this weakness and consequent decline in gait coordination is affected by dopamine levels. To this end, we compare cortico-cortical, cortico-muscular, and intermuscular connectivity and gait outcomes between body sides in people with PD under ON and OFF medication states, and in older adults. In our study, participants walked back and forth along a 12 m corridor. Gait events (heel strikes and toe-offs) and electrical cortical and muscular activities were measured and used to compute cortico-cortical, cortico-muscular, and intermuscular connectivity (i.e., coherences in the alpha, beta, and gamma bands), as well as features characterizing gait performance (e.g., the step-timing coordination, length, and speed). We observe that people with PD, mainly during the OFF medication, walk with reduced step-timing coordination. Additionally, our results suggest that dopamine intake in PD increases the overall cortico-muscular connectivity during the stance and swing phases of gait. We thus conclude that dopamine corrects defective feedback caused by impaired sensory-information processing and sensory-motor integration, thus increasing cortico-muscular coherences in the alpha bands and improving gait.

Home-based monitoring of persons with advanced Parkinson's disease using smartwatch-smartphone technology.

Movement deterioration is the hallmark of Parkinson's disease (PD), characterized by levodopa-induced motor-fluctuations (i.e., symptoms' variability related to the medication cycle) in advanced stages. However, motor symptoms are typically too sporadically and/or subjectively assessed, ultimately preventing the effective monitoring of their progression, and thus leading to suboptimal treatment/therapeutic choices. Smartwatches (SW) enable a quantitative-oriented approach to motor-symptoms evaluation, namely home-based monitoring (HBM) using an embedded inertial measurement unit. Studies validated such approach against in-clinic evaluations. In this work, we aimed at delineating personalized motor-fluctuations' profiles, thus capturing individual differences. 21 advanced PD patients with motor fluctuations were monitored for 2 weeks using a SW and a smartphone-dedicated app (Intel Pharma Analytics Platform). The SW continuously collected passive data (tremor, dyskinesia, level of activity using dedicated algorithms) and active data, i.e., time-up-and-go, finger tapping, hand tremor and hand rotation carried out daily, once in OFF and once in ON levodopa periods. We observed overall high compliance with the protocol. Furthermore, we observed striking differences among the individual patterns of symptoms' levodopa-related variations across the HBM, allowing to divide our participants among four data-driven, motor-fluctuations' profiles. This highlights the potential of HBM using SW technology for revolutionizing clinical practices.

Using virtual reality-based neurocognitive testing and eye tracking to study naturalistic cognitive-motor performance.

Natural human behavior arises from continuous interactions between the cognitive and motor domains. However, assessments of cognitive abilities are typically conducted using pen and paper tests, i.e., in isolation from "real life" cognitive-motor behavior and in artificial contexts. In the current study, we aimed to assess cognitive-motor task performance in a more naturalistic setting while recording multiple motor and eye tracking signals. Specifically, we aimed to (i) delineate the contribution of cognitive and motor components to overall task performance and (ii) probe for a link between cognitive-motor performance and pupil size. To that end, we used a virtual reality (VR) adaptation of a well-established neurocognitive test for executive functions, the 'Color Trails Test' (CTT). The VR-CTT involves performing 3D reaching movements to follow a trail of numbered targets. To tease apart the cognitive and motor components of task performance, we included two additional conditions: a condition where participants only used their eyes to perform the CTT task (using an eye tracking device), incurring reduced motor demands, and a condition where participants manually tracked visually-cued targets without numbers on them, incurring reduced cognitive demands. Our results from a group of 30 older adults (>65) showed that reducing cognitive demands shortened completion times more extensively than reducing motor demands. Conditions with higher cognitive demands had longer target search time, as well as decreased movement execution velocity and head-hand coordination. We found larger pupil sizes in the more cognitively demanding conditions, and an inverse correlation between pupil size and completion times across individuals in all task conditions. Lastly, we found a possible link between VR-CTT performance measures and clinical signatures of participants (fallers versus non-fallers). In summary, performance and pupil parameters were mainly dependent on task cognitive load, while maintaining systematic interindividual differences. We suggest that this paradigm opens the possibility for more detailed profiling of individual cognitive-motor performance capabilities in older adults and other at-risk populations.

Higher cognitive load interferes with head-hand coordination: virtual reality-based study.

Daily life activities often involve decision-based reaching movements in different contexts and circumstances. These activities span a wide array of cognitive load types we face while executing motor functions. Here we use a virtual reality-based neurocognitive testing platform to assess cognitive-induced changes in motor behavior as reflected by modulations in head-hand coordination. Our paradigm is based on the Color Trails Test (CTT), which is designed to assess two types of cognitive functions: Trails A-sustained visual attention (SVA), and Trails B-divided attention (DA). The virtual reality CTT adaptation (VR-CTT) requires execution of large multi-directional hand movements and head rotations. We employed a cross-correlation analysis on hand and head kinematics data collected from 122 healthy participants (ages: 20-90 years; divided as follows: young, middle-aged, and older adults) who completed the VR-CTT. The level of spatial coherence of head-hand movements was found to be high (R ≥ 0.76) in both Trails A and B, in all age groups. However, assessing head-hand phase shifts revealed longer time lags (i.e., in which head leads hand) in Trails B versus Trails A, in all age groups. We conclude that allocating cognitive resources to DA task reduces head-hand synchrony as compared to SVA conditions.

Supplementary Motor Area Activity Differs in Parkinson's Disease with and without Freezing of Gait.

The study aimed to investigate the neural changes that differentiate Parkinson's disease patients with freezing of gait and age-matched controls, using ambulatory electroencephalography event-related features. Compared to controls, definite freezers exhibited significantly less alpha desynchronization at the motor cortex about 300 ms before and after the start of overground walking and decreased low-beta desynchronization about 300 ms before and about 300 and 700 ms after walking onset. The late slope of motor potentials also differed in the sensory and motor areas between groups of controls, definite, and probable freezers. This difference was found both in preparation and during the execution of normal walking. The average frontal peak of motor potential was also found to be largely reduced in the definite freezers compared with the probable freezers and controls. These findings provide valuable insights into the underlying structures that are affected in patients with freezing of gait, which could be used to tailor drug development and personalize drug care for disease subtypes. In addition, the study's findings can help in the evaluation and validation of nonpharmacological therapies for patients with Parkinson's disease.

Differential gait adaptation patterns in Parkinson's disease - a split belt treadmill pilot study.

BACKGROUND: Interventions using split belt treadmills (SBTM) aim to improve gait symmetry (GA) in Parkinson's disease (PD). Comparative effects in conjugated SBTM conditions were not studied systematically despite potentially affecting intervention outcomes. We compared gait adaptation effects instigated by SBTM walking with respect to the type (increased\decreased speed) and the side (more/less affected) of the manipulated belt in PD. METHODS: Eight individuals with PD performed four trials of SBTM walking, each consisted of baseline tied belt configuration, followed by split belt setting - either WS or BS belt's speed increased or decreased by 50% from baseline, and final tied belt configuration. Based on the disease's motor symptoms, a 'worst' side (WS) and a 'best' side (BS) were defined for each participant. RESULTS: SB initial change in GA was significant regardless of condition (p ≤ 0.02). This change was however more pronounced for BS-decrease compared with its matching condition WS-increase (p = 0.016). Similarly, the same was observed for WS-decrease compared to BS-increase (p = 0.013). Upon returning to tied belt condition, both BS-decrease and WS-increased resulted in a significant change in GA (p = 0.04). Upper limb asymmetry followed a similar trend of GA reversal, although non-significant. CONCLUSIONS: Stronger effects on GA were obtained by decreasing the BS belt's speed of the best side, rather than increasing the speed of the worst side. Albeit a small sample size, which limits the generalisability of these results, we propose that future clinical studies would benefit from considering such methodological planning of SBTM intervention, for maximising of intervention outcomes. Larger samples may reveal arm swinging asymmetries alterations to match SBTM adaptation patterns. Finally, further research is warranted to study post-adaption effects in order to define optimal adaptation schemes to maximise the therapeutic effect of SBTM based interventions.

Heart-rate variability as a new marker for freezing predisposition in Parkinson's disease.

INTRODUCTION: Freezing of gait (FoG) is a debilitating symptom of advanced Parkinson's disease (PD) characterized by a sudden, episodic stepping arrest despite the intention to continue walking. The etiology of FoG is still unknown, but accumulating evidence unraveled physiological signatures of the autonomic nervous system (ANS) around FoG episodes. Here we aim to investigate for the first time whether detecting a predisposition for upcoming FoG events from ANS activity measured at rest is possible. METHODS: We recorded heart-rate for 1-min while standing in 28 persons with PD with FoG (PD + FoG), while OFF, and in 21 elderly controls (EC). Then, PD + FoG participants performed walking trials containing FoG-triggering events (e.g., turns). During these trials, n = 15 did experience FoG (PD + FoG+), while n = 13 did not (PD + FoG-). Most PD participants (n = 20: 10 PD + FoG+ and 10 PD + FoG-) repeated the experiment 2-3 weeks later, while ON, and none experienced FoG. We then analyzed heart-rate variability (HRV), i.e., the fluctuations in time intervals between adjacent heartbeats, mainly generated by brain-heart interactions. RESULTS: During OFF, HRV was significantly lower in PD + FoG + participants, reflecting imbalanced sympathetic/parasympathetic activity and disrupted self-regulatory capacity. PD + FoG- and EC participants showed comparable (higher) HRV. During ON, HRV did not differ among groups. HRV values did not correlate with age, PD duration, levodopa consumption, nor motor -symptoms severity scores. CONCLUSIONS: Overall, these results document for the first time a relation between HRV at rest and FoG presence/absence during gait trials, expanding previous evidence regarding the involvement of ANS in FoG.

Improving old tricks as new: Young adults learn from repeating everyday activities.

The notion that young healthy adults can substantially improve in activities that are part of their daily routine is often overlooked because it is assumed that such activities have come to be fully mastered. We followed, in young healthy adults, the effects of repeated executions of the Timed-Up-and-Go (TUG) task, a clinical test that assesses the ability to execute motor activities relevant to daily function-rising from a seated position, walking, turning and returning to a seated position. The participants (N = 15) performed 18 consecutive trials of the TUG in one session, and were retested on the following day and a week later. The participants were video recorded and wore inertial measurement units. Task execution times improved robustly; performance was well fitted by a power function, with large gains at the beginning of the session and nearing plateau in later trials, as one would expect in the learning of a novel task. Moreover, these gains were well retained overnight and a week later, with further gains accruing in the subsequent test-sessions. Significant intra-session and inter-session changes occurred in step kinematics as well; some aspects underwent inter-sessions recalibrations, but other aspects showed delayed inter-session changes, suggesting post-practice memory consolidation processes. Even common everyday tasks can be improved upon by practice; a small number of consecutive task repetitions can trigger lasting gains in young healthy individuals performing highly practiced routine tasks. This new learning in highly familiar tasks proceeded in a time-course characteristic of the acquisition of novel 'how to' (procedural) knowledge.

Upward perturbations trigger a stumbling effect.

BACKGROUND: Vertical perturbations are one major cause of falling. Incidentally, while conducting a comprehensive study comparing effects of vertical versus horizontal perturbations, we commonly observed a stumbling-like response induced by upward perturbations. The present study describes and characterizes this stumbling effect. METHODS: Fourteen individuals (10 male; 27 ± 4 yr) walked self-paced on a treadmill embedded in a moveable platform and synchronized to a virtual reality system. Participants experienced 36 perturbations (12 types). Here, we report only on upward perturbations. We determined stumbling based on visual inspection of recorded videos, and calculated stride time and anteroposterior, whole-body center of mass (COM) distance relative to the heel, i.e., COM-to-heel distance, extrapolated COM (xCOM) and margin of stability (MOS) before and after perturbation. RESULTS: From 68 upward perturbations across 14 participants, 75% provoked stumbling. During the first gait cycle post-perturbation, stride time decreased in the perturbed foot and the unperturbed foot (perturbed = 1.004 s vs. baseline = 1.119 s and unperturbed = 1.017 s vs. baseline = 1.125 s, p < 0.001). In the perturbed foot, the difference was larger in stumbling-provoking perturbations (stumbling: 0.15 s vs. non-stumbling: 0.020 s, p = 0.004). In addition, the COM-to-heel distance decreased during the first and second gait cycles after perturbation in both feet (first cycle: 0.58 m, second cycle: 0.665 m vs. baseline: 0.72 m, p-values<0.001). During the first gait cycle, COM-to-heel distance was larger in the perturbed foot compared to the unperturbed foot (perturbed foot: 0.61 m vs. unperturbed foot: 0.55 m, p < 0.001). MOS decreased during the first gait cycle, whereas the xCOM increased during the second through fourth gait cycles post-perturbation (maximal xCOM at baseline: 0.5 m, second cycle: 0.63 m, third cycle: 0.66 m, fourth cycle: 0.64 m, p < 0.001). CONCLUSIONS: Our results show that upward perturbations can induce a stumbling effect, which - with further testing - has the potential to be translated into balance training to reduce fall risk, and for method standardization in research and clinical practice.

Studying cognitive-motor interactions using a tablet-based application of the Color Trails Test.

The Color Trails Test (CTT) is a pen and paper (P&P) test designed to measure cognitive function. The test consists of two parts that evaluate primarily sustained visual attention (Trails A) and divided attention (Trails B). Based on clinical interest in converting neuropsychological testing from P&P to computerized testing, we developed a digital version of the CTT ('Tablet-CTT'). Twenty-four young, healthy participants performed Trails A and B of both the original P&P and the Tablet-CTT. Hand kinematics were calculated using the continuous location of an electronic pen on the tablet touch screen. To compare motor control aspects, we differentiated for each test session the 'movement planning' and 'movement execution' times (accumulated across all single target-to-target trajectories). Concurrent validity was demonstrated by the high correlation between completion times of the P&P and Tablet-CTT, in both Trails A (r = 0.6; p < 0.005) and Trails B (r = 0.8; p < 0.001). Trails B yielded significantly longer completion times in both formats (p < 0.001). Examining hand kinematics in Tablet-CTT revealed that the difference in durations was mostly due to prolonged planning time, but also due to significantly lower execution velocity in Trails B (p < 0.001). Lastly, we found increased hand velocity during the planning phase in Trails B compared to Trails A (p < 0.001). This study demonstrates how transforming the CTT to a digital platform could be useful for studying cognitive-motor interactions in healthy individuals. Moreover, it could potentially serve as a diagnosis tool by introducing a more comprehensive testing method that incorporates online recordings of hand movements.

Balancing new technology: Virtual reality for balance measurement case report.

RATIONALE: Falling and the inability to maintain balance are the second leading cause of unintentional injury deaths globally. There are a number of chronic and acute conditions characterized by balance difficulties, including neurological diseases, and sport injuries. Therefore, methods to monitor and quantify balance are critical for clinical decision-making regarding risk management and balance rehabilitation. New advances in virtual reality (VR) technology has identified VR as a novel therapeutic platform. VRSway is a VR application that uses sensors attached to a virtual reality headset, and handheld remote controllers for measurement and analysis of postural stability by measuring changes in spatial location relative to the center of mass and calculates various postural stability indexes. This case report evaluates balance measures in 2 healthy participants with no previous history of balance disorders using the VRSway software application and compares to output generated by the current gold standard of balance measurement, force platform technology. CASE PRESENTATION: The primary objective of this case study was to validate the VRSway stability score for evaluation of balance. Here, we present posturography measures of the VRSway in comparison with force plate readouts in 2 healthy participants. Body Sway measurements were recorded simultaneously in both the force plate and VRSway systems. Data calculated by proprietary software is highly correlative to the data generated by force plates for each of the following measurements for participant-1 and participant-2, respectively: Sway index (r 1 = 0.985, P < .001; r 2 = 0.970, P < .001), total displacement (r 1 = 0.982, P < .001; r 2 = 0.935, P < .001), center of pressure mean velocity (r 1 = 0.982, P < .001; r 2 = 0.935, P < .001), ellipse radius 1 (r 1 = 0.979, P < .001; r 2 = 0.965, P < .001), ellipse radius 2 (r 1 = 0.982, P < .001; r 2 = 0.969, P < .001), and ellipse area (r 1 = 0.983, P < .001; r 2 = 0.969, P < .001). CONCLUSIONS: Data from this case study suggest that VRSway measurements are highly correlated with output from force plate technology posing that VRSway is a novel approach to evaluate balance measures with VR. More research is required to understand possible uses of VR-based use for balance measurement in a larger and more diverse cohort.

Developing multiple shortened forms of virtual reality-based color trails test.

The Color Trails Test (CTT) is a pencil-and-paper (P&P) neuropsychological test. The CTT is divided into two parts that assess sustained visual attention (Trails A) and divided attention (Trails B). The CTT can also be performed in a virtual reality setting (VR-CTT) introducing a wider spatial range of targets. In cases of multiple assessments, repeating the same CTT configuration can bias the results due to fatigue and learning effects. The aim of this study is to create five different short versions of the VR-CTT. The different forms were created by rotating or flipping the original targets spatial layout on one of the axes and by ending it at ball #13. Healthy young participants (N = 15) performed the shortened VR-CTT forms (in a counterbalanced order), the P&P CTT and the original VR-CTT. We found no difference between the completion times of the five forms (p > 0.2), and a significant difference between Trails A and B across all forms (p < 0.04). Additionally, there was no evidence of a learning effect between trials (p > 0.4). Moreover, the shortened VR-CTT forms showed correlations with the P&P CTT (p < 0.05) and with the original VR-CTT (p < 0.06). These findings suggest that all five forms have an equal level of difficulty and that the different forms managed to mitigate the learning effects reported for repeated testing of the same spatial layout. This opens the possibility of applying the shortened VR-CTT forms for research settings and sets the basis for developing it into a clinical diagnostics tool.

Development and validation of virtual reality-based Rey Auditory Verbal Learning Test.

Objective: Translations and adaptations of traditional neuropsychological tests to virtual reality (VR) technology bear the potential to increase their ecological validity since the technology enables simulating everyday life conditions in a controlled manner. The current paper describes our translation of a commonly used neuropsychological test to VR, the Rey Auditory Verbal Learning Test (RAVLT). For this aim, we developed a VR adaptation of the RAVLT (VR-RAVLT) Which is based on a conversation with a secretary in a virtual office using a fully immersive VR system. To validate the VR-RAVLT, we tested its construct validity, its age-related discriminant validity and its test-retest validity in reference to the original gold standard RAVLT (GS-RAVLT). Method: Seventy-eight participants from different age groups performed the GS-RAVLT and the VR-RAVLT tests in a counterbalanced order in addition to other neuropsychological tests. Construct validity was validated using Pearson's correlations coefficients and serial position effects; discriminant validity was validated using receiver operating characteristic area under the curve values and test-retest reliability was validated using intraclass correlation coefficients. Results: Comparing both RAVLTs' format results indicates that the VR-RAVLT has comparable construct, discriminant and test-retest validities. Conclusion: the novel VR-RAVLT and the GS-RAVLT share similar psychometric properties suggesting that the two tests measure the same cognitive construct. This is an indication of the feasibility of adapting the RAVLT to the VR environment. Future developments will employ this approach for clinical diagnosis and treatment.

Age related changes in gait variability, asymmetry, and bilateral coordination - When does deterioration starts?

BACKGROUND: Gait pattern coordination is affected by several factors (e.g., neurodegeneration), while aging is known to have a significant negative impact. Various gait parameters, such as gait asymmetry (GA) and stride time coefficient of variation (CV), are widely used in both research and clinical settings in order to evaluate human locomotion. Another parameter is the phase coordination index (PCI), which specifically assesses bilateral coordination of gait (BCG), by quantifying the consistency and accuracy of the anti-phased stepping pattern. OBJECTIVE: In this study we hypothesized that there is a steady deterioration in the bilateral coordination of walking through ageing, and in gait rhythmicity, which would be evident by an increase in the values of the coordination parameters which are examined. METHODS: We analyzed gait cycles of 66 healthy participants in ages between 40 and 85 years which were divided into five age groups (40-44; 45-54; 55-64; 75 +). The participants performed corridor walking (i.e., back and forth) wearing a computerized motion sensor-based gait analysis system. PCI, CV and GA parameters were calculated for the straight-line walking segments. RESULTS: PCI values remained relatively stable between the ages of 40-75 (3.16 ± 1.11%), while in the age group of 75 + years old we observed a significant increase (i.e., deterioration in BCG) in PCI values (5.68 ± 2.01%, p < 0.047). Same pattern was seen for the CV parameter. However, GA was not statistically significantly different between all age groups. CONCLUSION: It appears that PCI and CV are more sensitive measures to detect changes in gait through the aging process. The results suggest that potential screening to detect salient gait deterioration should start from the age of 70. On the other hand, GA may be used to identify neurological impairments if found increased at any age.

The trail less traveled: Analytical approach for creating shortened versions for virtual reality-based color trails test.

The Color Trails Test ("CTT") is among the most popular neuropsychological assessment tests of executive function, targeting sustained visual attention (Trails A), and divided attention (Trails B). During the pen-and-paper (P&P) test, the participant traces 25 consecutive numbered targets marked on a page, and the completion time is recorded. In many cases, multiple assessments are performed on the same individual, either under varying experimental conditions or at several timepoints. However, repeated testing often results in learning and fatigue effects, which confound test outcomes. To mitigate these effects, we set the grounds for developing shorter versions of the CTT (<25 targets), using virtual reality (VR) based CTT (VR-CTT). Our aim was to discover the minimal set of targets that is sufficient for maintaining concurrent validity with the CTT including differentiation between age groups, and the difference between Trails A and B. To this aim, healthy participants in three age groups (total N = 165; young, middle-aged, or older adults) performed both the P&P CTT, and one type of VR-CTT (immersive head-mounted-device VR, large-scale 3D VR, or tablet). A subset of 13 targets was highly correlated with overall task completion times in all age groups and platforms (r > 0.8). We tested construct validity and found that the shortened-CTT preserved differences between Trails A and B (p < 0.001), showed concurrent validity relative to the P&P scores (r > 0.5; p < 0.05), and differentiated between age groups (p < 0.05). These findings open the possibility for shortened "CTT-versions", to be used in repeated-measures experiments or longitudinal studies, with potential implications for shortening neurocognitive assessment protocols.

Dopaminergic medication reduces interhemispheric hyper-synchronization in Parkinson's disease.

INTRODUCTION: We previously reported on interhemispheric cortical hyper synchronization in PD. The aim of the present study was to address the hypothesis that increased interhemispheric cortical synchronization in PD is related to dopamine deficiency and is correlated with motor function. METHODS: We studied participants with PD and characterized cortical synchronization with reference to brain regions. Electroencephalography (EEG) was recorded from 20 participants with PD while OFF and ON their dopaminergic medications (two separate visits), during quiet standing and straight-line walking. Cortical interactions in the theta, alpha, beta, and gamma brain wave frequency bands were evaluated using interhemispheric phase synchronization (inter-PS). RESULTS: Inter-PS values were found to be significantly higher during the OFF state as compared to the ON state in standing and walking trials for theta, alpha and beta bands. In addition, inter-PS reduction from OFF to ON was associated with mobility improvement evaluated by the Timed Up and Go test, and with daily levodopa equivalent dose across individuals. Higher differences in inter-PS values between OFF and ON states were evident mainly in the occipital-parietal cortex. CONCLUSIONS: Persons with PD have increased inter-PS during the OFF state compared to their ON state, and this increase in inter-PS is associated with the clinical improvement between OFF and ON. We speculate that these findings, together with previous evidence of higher inter-PS in PD as compared to healthy older adults, reflect neuronal processes consequential to asymmetric subcortical dopamine deficiency.

Muscle activation profile is modulated by unexpected balance loss in walking.

BACKGROUND: During an unexpected loss of balance, avoiding a fall requires people to readjust their footing rapidly and effectively. A deeper understanding of muscle activation patterns in response to unexpected balance loss will provide insights into the mechanisms of balance recovery responses. This could have implications for treatment of people with balance deficits. RESEARCH QUESTION: Explore the differences in balance recovery responses to perturbations in different phases of the gait cycle (single-support vs. double-support) in terms of biomechanical behavior (i.e., stepping and dynamic stability characteristics) and lower-limb muscle activation patterns. METHODS: Muscle activation patterns of the ankle and knee muscles and muscle fiber type recruitment resulting from unannounced, mediolateral (i.e., right/left) horizontal-surface perturbations during walking was investigated in twenty healthy adults (27.00 ± 2.79 years, ten females). Surface electromyography (sEMG) total spectral power for specific frequency bands (40-60 Hz, 60-150 Hz, 150-250 Hz, 250-400 Hz and 400-1000 Hz), from tibialis anterior (TA) and vastus lateralis (VL) muscles were analyzed. Three mixed-effects models assessed behavioral and lower-limb muscle activation patterns resulting from perturbations in the gait cycle's single- and double-support phases. Statistical significance was set a priori at p < 0.05. RESULTS: Compared to non-perturbed walking, we found a significant increase in the total spectral power of lower-extremity muscles during the first three seconds after perturbation. During the double-support phase of gait, we found a different muscle fiber type recruitment pattern between VL and TA muscles. However, there were no significant differences between VL and TA muscles for perturbations implemented in single-support phases. SIGNIFICANCE: Our findings support the notion that muscle operating frequency is modulated in real-time to fit functional goal requirements, such as a rapid change of footing in response to unexpected loss of balance in single and double-support phases of gait.

Responses to balance challenges in persons with panic disorder: A pilot study of computerized static and dynamic balance measurements.

INTRODUCTION: Several studies have shown an association between panic disorder (PD) and reduced balance abilities, mainly based on functional balance scales. This pilot study aims to demonstrate the feasibility of studying balance abilities of persons with PD (PwPD) using computerized static and, for the first time, dynamic balance measurements in order to characterize balance control strategies employed by PwPD. METHODS: Twelve PwPD and 11 healthy controls were recruited. PD diagnosis was confirmed using the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV), and the severity of symptoms was evaluated using the Hamilton Anxiety Scale (HAM-A), PD Severity Scales (PDSS), and Panic and Agoraphobia Scale (PAS). Balance was clinically assessed using the Activities-Specific Balance Confidence (ABC) scale and physically by the Mini-Balance Evaluation Systems Test (Mini-BESTest). Dizziness was evaluated using the Dizziness Handicap Inventory (DHI) scale. Postural control was evaluated statically by measuring body sway and dynamically by measuring body responses to rapid unexpected physical perturbations. RESULTS: PwPD had higher scores on the HAM-A (17.6 ± 10.3 vs. 3.0 ± 2.9; p < .001), PDSS (11.3 ± 5.1 vs. 0; p < .001), and PAS (20.3 ± 8.7 vs. 0; p < .001) questionnaires and lower scores on the balance scales compared to the controls (ABC scale: 156.2 ± 5.9 vs. 160 ± 0.0, p = .016; Mini-BESTest: 29.4 ± 2.1 vs. 31.4 ± 0.9, p = .014; DHI: 5.3 ± 4.4 vs. 0.09 ± 0.3, p < .001). In the static balance tests, PwPD showed a not-significantly smaller ellipse area of center of pressure trajectory (p = .36) and higher body sway velocity (p = .46), whereas in the dynamic balance tests, PwPD had shorter recovery time from physical perturbations in comparison to controls (2.1 ± 1.2s vs. 1.6 ± 0.9 s, p = .018). CONCLUSION: The computerized balance tests results point to an adoption of a ''postural rigidity'' strategy by the PwPD, that is, reduced dynamic adaptations in the face of postural challenges. This may reflect a nonsecure compensatory behavior. Further research is needed to delineate this strategy.