Postural Fluctuations Research Articles

7576 A Rare and Atypical Presentation of Bladder Paraganglioma in a Patient on Long-Term Left Ventricular Assist Device

Abstract Disclosure: S.D. Leungsuwan: None. S.J. Lee: None. S.D. Lim: None. L. Loh: None. Background: Paragangliomas (PGLs) are rare neuroendocrine tumors arising from chromaffin cells. Capable of producing catecholamines, functional PGLs often cause a myriad of autonomic symptoms and complications, including cardiomyopathy. We report a case of bladder PGL in a patient on Left Ventricular Assist Device (LVAD). Clinical Case: A 64-year-old Chinese Female with a history of non-ischaemic cardiomyopathy on long-term continuous LVAD and Cardiac Resynchronisation Therapy Defibrillator (CRT-D) was admitted for recurrent low LVAD flow <2 Litres per minute and labile mean arterial pressure (MAP) 57-151mmHg. She has been on long-term Nebivolol, Entresto, Hydralazine, and Sildenafil without recent dose adjustment. Workup for acute illnesses was non-contributory. 24-hour urine metanephrine and normetanephrine (NM) were 939nmol/d [normal 400-1500nmol/d] and 33883nmol/d [normal 600-1900nmol/d] respectively. Plasma free metanephrine and NM were 0.37nmol/L [normal <0.33nmol/L] and >10.00nmol/L [normal <0.99nmol/L] accordingly. A review of previous ultrasonography and Computed Tomography (CT) imaging revealed a right adnexal mass indenting the bladder which the patient formerly declined further assessment; adrenal glands were normal. FDG-PET CT was done and showed an isolated focus of increased tracer uptake corresponding with the right pelvic mass. An impression of likely bladder PGL was made. A multidisciplinary team including Cardiology, Anaesthesiology, Interventional Radiology (IR), Urology, Gynaecology, and Endocrinology was convened; the patient was recommended surgical resection of the tumor. Preoperatively, she was started on phenoxybenzamine 10mg BD and advised judicious fluid and salt intake. Nebivolol was continued while hydralazine was stopped. This achieved targets of i) MAP 70-80mmHg, ii) approximately 10mmHg MAP postural fluctuation, iii) sitting and standing heart rates 60-70 beats-per-minute (BPM) and 70-80BPM, and iv) no more than 1 PVC every 5 minutes. Two weeks later, she underwent IR-guided angioembolisation and tumor resection uneventfully. Intraoperatively, the patient had haemodynamic fluctuations requiring dynamic administrations of phentolamine, norepinephrine, epinephrine, vasopressin, glyceryl trinitrate, and sodium nitroprusside. Histopathology was consistent with PGL with intact SDH-A and SDH-B expression. Postoperatively, phenoxybenzamine was discontinued and no recurrent LVAD low flow was noted. Subsequent plans for repeat plasma metanephrines and genetic studies were made. Discussion: This case is the first to report an atypical presentation of PGL with LVAD low flow and labile blood pressure. The significant elevations of urine NM (17.8x upper normal limit) and plasma NM (>10.1x upper normal limit) also underline the concept of fold-elevations and post-test probability of PGL. Presentation: 6/3/2024

Cross-frequency modulation of postural fluctuations and scalp EEG in older adults: error amplification feedback for rapid balance adjustments.

Virtual error amplification (VEA) in visual feedback enhances attentive control over postural stability, although the neural mechanisms are still debated. This study investigated the distinct cortical control of unsteady stance in older adults using VEA through cross-frequency modulation of postural fluctuations and scalp EEG. Thirty-seven community-dwelling older adults (68.1 ± 3.6years) maintained an upright stance on a stabilometer while receiving either VEA or real error feedback. Along with postural fluctuation dynamics, phase-amplitude coupling (PAC) and amplitude-amplitude coupling (AAC) were analyzed for postural fluctuations under 2Hz and EEG sub-bands (theta, alpha, and beta). The results revealed a higher mean frequency of the postural fluctuation phase (p = .005) and a greater root mean square of the postural fluctuation amplitude (p = .003) with VEA compared to the control condition. VEA also reduced PAC between the postural fluctuation phase and beta-band EEG in the left frontal (p = .009), sensorimotor (p = .002), and occipital (p = .018) areas. Conversely, VEA increased the AAC of posture fluctuation amplitude and beta-band EEG in FP2 (p = .027). Neither theta nor alpha band PAC or AAC were affected by VEA. VEA optimizes postural strategies in older adults during stabilometer stance by enhancing visuospatial attentive control of postural responses and facilitating the transition of motor states against postural perturbations through a disinhibitory process. Incorporating VEA into virtual reality technology is advocated as a valuable strategy for optimizing therapeutic interventions in postural therapy, particularly to mitigate the risk of falls among older adults.

Concurrent Supra-Postural Auditory-Hand Coordination Task Affects Postural Control: Using Sonification to Explore Environmental Unpredictability in Factors Affecting Fall Risk.

Clinical screening tests for balance and mobility often fall short of predicting fall risk. Cognitive distractors and unpredictable external stimuli, common in busy natural environments, contribute to this risk, especially in older adults. Less is known about the effects of upper sensory-motor coordination, such as coordinating one's hand with an external stimulus. We combined movement sonification and affordable inertial motion sensors to develop a task for the precise measurement and manipulation of full-body interaction with stimuli in the environment. In a double-task design, we studied how a supra-postural activity affected quiet stance. The supra-postural task consisted of rhythmic synchronization with a repetitive auditory stimulus. The stimulus was attentionally demanding because it was being modulated continuously. The participant's hand movement was sonified in real time, and their goal was to synchronize their hand movement with the stimulus. In the unpredictable condition, the tempo changed at random points in the trial. A separate sensor recorded postural fluctuations. Young healthy adults were compared to older adult (OA) participants without known risk of falling. The results supported the hypothesis that supra-postural coordination would entrain postural control. The effect was stronger in OAs, supporting the idea that diminished reserve capacities reduce the ability to isolate postural control from sensory-motor and cognitive activity.

Roles of the cerebellar vermis in predictive postural controls against external disturbances

The central nervous system predictively controls posture against external disturbances; however, the detailed mechanisms remain unclear. We tested the hypothesis that the cerebellar vermis plays a substantial role in acquiring predictive postural control by using a standing task with floor disturbances in rats. The intact, lesioned, and sham groups of rats sequentially underwent 70 conditioned floor-tilting trials, and kinematics were recorded. Six days before these recordings, only the lesion group underwent focal suction surgery targeting vermal lobules IV–VIII. In the naïve stage of the sequential trials, the upright postures and fluctuations due to the disturbance were mostly consistent among the groups. Although the pattern of decrease in postural fluctuation due to learning corresponded among the groups, the learning rate estimated from the lumbar displacement was significantly lower in the lesion group than in the intact and sham groups. These results suggest that the cerebellar vermis contributes to predictive postural controls.

Age-Related Topological Organization of Phase-Amplitude Coupling Between Postural Fluctuations and Scalp EEG During Unsteady Stance.

Through phase-amplitude analysis, this study investigated how low-frequency postural fluctuations interact with high-frequency scalp electroencephalography (EEG) amplitudes, shedding light on age-related mechanic differences in balance control during uneven surface navigation. Twenty young ( 24.1 ± 1.9 years) and twenty older adults ( 66.2 ± 2.7 years) stood on a training stabilometer with visual guidance, while their scalp EEG and stabilometer plate movements were monitored. In addition to analyzing the dynamics of the postural fluctuation phase, phase-amplitude coupling (PAC) for postural fluctuations below 2 Hz and within EEG sub-bands (theta: 4-7 Hz, alpha: 8-12 Hz, beta: 13-35 Hz) was calculated. The results indicated that older adults exhibited significantly larger postural fluctuation amplitudes(p <0.001) and lower mean frequencies of the postural fluctuation phase ( p = 0.005 ) than young adults. The PAC between postural fluctuation and theta EEG (FCz and bilateral temporal-parietal-occipital area), as well as that between postural fluctuation and alpha EEG oscillation, was lower in older adults than in young adults (p <0.05). In contrast, the PAC between the phase of postural fluctuation and beta EEG oscillation, particularly in C3 ( p=0.006 ), was higher in older adults than in young adults. In summary, the postural fluctuation phase and phase-amplitude coupling between postural fluctuation and EEG are sensitive indicators of the age-related decline in postural adjustments, reflecting less flexible motor state transitions and adaptive changes in error monitoring and visuospatial attention.

Деякі тенденції та характерні особливості фізичного розвитку чоловіків 36–45 років із круглою спиною

The analysis and synthesis of professional scientific and methodological literature, tangent to the problem of the proposed research, has highlighted the scientific community’s development of a number of theories to confirm the expediency of positioning a person’s posture not only as a simple static arrangement of various body biolanks, but above all as the foundation of human health and the basis of human well-being. In general, postural stability can be considered as its ability to persist and remain qualitatively unchanged in response to interference or fluctuations (including postural fluctuations) in control. Monitoring the state of posture is a very important and basic requirement in everyday life. The purpose of the article is to study the age-related changes in the physical development indicators of men 36-45 years old with a round back. Research methods. theoretical analysis of literary sources, anthropometry, pedagogical experiment, mathematical statistics. Results of work. The study showed that despite some differences in body length, body weight and body mass index in favor of men 36-40 years and in the indicators of circumferential hip size in favor of men 41-45 years, statistically significant differences between them are not proven (p &gt; 0.05). At the same time, it was established that the circumferential waist sizes of men 41-45 years old are 3.63 cm (only 4.7 %) statistically significant (p &lt; 0.05) more than in men 36-40 years old. And, as with the bypass dimensions of the lower leg, which is 8.24 % statistically significant (p &lt; 0.05) predominates in men 41-45 years old. Conclusions. Summarizing the above, it should be emphasized that in men 36-45 years old there is excessive body weight. At the same time, a trend was recorded according to which the circumferential dimensions of the waist and lower leg increase in men with age.

Coordination Rigidity in the Gait, Posture, and Speech of Persons with Parkinson’s Disease

Parkinson’s disease (PD) is associated with reduced coordination abilities. These can result either in random or rigid patterns of movement. The latter, described here as coordination rigidity (CR), have been studied less often. We explored whether CR was present in gait, quiet stance, and speech—tasks involving coordination among multiple joints and muscles. Kinematic and voice recordings were used to compute measures describing the dynamics of systems with multiple degrees of freedom and nonlinear interactions. After clinical evaluation, patients with moderate stage PD were compared against matched healthy participants. In the PD group, gait dynamics was associated with decreased dynamic divergence—lower instability—in the vertical axis. Postural fluctuations were associated with increased regularity in the anterior-posterior axis, and voice dynamics with increased predictability, all consistent with CR. The clinical relevance of CR was confirmed by showing that some of those features contribute to disease classification with supervised machine learning (82/81/85% accuracy/sensitivity/specificity).

Adaptations of postural sway dynamics and cortical response to unstable stance with stroboscopic vision in older adults.

Background: Stroboscopic vision (SV), intermittent visual blocking, has recently been incorporated into postural training in rehabilitation. This study investigated interactions of postural fluctuation dynamics and cortical processing for the elderly during stabilometer stance with SV. Methods: Thirty-five healthy elderly maintained an upright stance on a stabilometer. Along with postural fluctuation dynamics, EEG relative power and EEG-EEG connectivity were used to contrast neuromechanical controls of stabilometer stance with SV and full-vision. Results: Compared with the full-vision, SV led to greater postural fluctuations with lower sample entropy and mean frequency (MF). SV also reduced regional power in the mid-frontal theta cluster, which was correlated to SV-dependent changes in the size of postural fluctuations. SV also enhanced the alpha band supra-threshold connectivity in the visual dorsal and frontal–occipital loops of the right hemisphere, and the supra-threshold connectivity from Fp2 positively related to variations in the MF of postural fluctuations. Conclusion: SV adds challenge to postural regulation on the stabilometer, with the increasing regularity of postural movements and fewer corrective attempts to achieve the postural goal. The elderly shift over-reliance on visual inputs for posture control with more non-visual awareness, considering deactivation of the dorsal visual stream and visual error processing.

Decreased Postural Complexity in Overweight to Obese Children and Adolescents: A Cross-Sectional Study.

IntroductionAlthough a few studies suggest that young overweight to obese children and adolescents (YO) may have impaired postural control compared to young normal-weight (YN) peers, little information exists about how these two groups differ in the quality of the underlying balance strategies employed. Hence, the aim of the present study was a first comprehensive examination of the structural complexity of postural sways in these two cohorts during quiet bilateral standing.MethodsNineteen YO secondary school students (13.0 ± 1.4 years; male = 10, female = 9) were carefully matched to YN controls (13.0 ± 1.5 years) for age, sex, height, and school. Mediolateral (ML) and anteriorposterior (AP) acceleration signals were recorded with an inertial measurement unit (IMU) positioned at the trunk while standing barefoot in two conditions: firm and foam support surface. The magnitude of postural fluctuations was obtained using the root mean square (RMS). The temporal structure of the signals was analyzed via sample entropy (SEn), largest Lyapunov exponent (LyE), and detrended fluctuation analysis (α-DFA) algorithm. Reliability was assessed using a test–retest design.ResultsIn both groups, foam standing caused higher postural fluctuations (higher RMS values) and reduced structural complexity (lower SEn values, higher LyE values, higher α-DFA values). In comparison to YN, YO exhibited a higher RMSAP. Especially in ML direction, the acceleration signals of the YO had higher repeatability (smaller SEn values), greater long-range correlations (higher α-DFA values), and lower local stability (higher LyE values). However, these observations were largely independent of the task difficulty. Except for α-DFAAP, the IMU approach proved reliable to characterize posture control.DiscussionOur outcomes confirm postural control deficits in YO compared to their YN peers and indicate impaired regulatory mechanisms reflected as rigidity. Such less complex patterns usually reflect diverse pathologies, are detrimental to compensate for internal or external perturbations, and are attributed to lower adaptability and task performance. Without targeted balance stimuli, YO likely end in a lifelong vicious circle of mutually dependent poor balance regulation and low physical activity.

Determination of vestibular function in children with purulent otitis media

The aim of the study is to assess the vestibular function of children with acute purulent otitis media by computer static stabilometry compared with typically developed peers. Materials and methods. In the course of the study 52 children aged 4 to 7 were examined by static stabilometry on the device «MPFI Stabilograph 1» (Kharkiv, Ukraine). 22 of them were diagnosed with purulent otitis media and their 30 peers were found to be practically healthy. Indicators of variations and forms of pressure center distribution, spectral-correlation indicators of stabilograms, as well as integral indicators of stability (length, velocity and angle of postural oscillations) and quality of equilibrium function in two sensory states (open and closed eyes) calculated in StabiliS software were taken into account. Results. Purulent otitis media causes posterior displacement of absolute coordinates of the pressure center. In the state with closed eyes, children with purulent otitis differ from their healthy peers in 14 of 24 stabilometric parameters, including stabilogram length, speed, angle and amplitude of oscillations, inferior to them in the balance. Children with purulent otitis media are more sensitive to the visual canal of postural control than their peers. Involvement of visual afferents in postural control significantly improves balance in children with purulent otitis by reducing deviations, postural fluctuations, which is reflected in the probable changes of 9 out of 24 stabilometric parameters compared to control. Conclusion. In preschool age, purulent otitis media leads to latent vestibular dysfunction, which is manifested by a violation of the stability of the vertical posture with the closed eyes and is compensated by visual-vestibular-proprioceptive integration in postural control.

Cortical reorganization to improve dynamic balance control with error amplification feedback

BackgroundError amplification (EA), virtually magnify task errors in visual feedback, is a potential neurocognitive approach to facilitate motor performance. With regional activities and inter-regional connectivity of electroencephalography (EEG), this study investigated underlying cortical mechanisms associated with improvement of postural balance using EA.MethodsEighteen healthy young participants maintained postural stability on a stabilometer, guided by two visual feedbacks (error amplification (EA) vs. real error (RE)), while stabilometer plate movement and scalp EEG were recorded. Plate dynamics, including root mean square (RMS), sample entropy (SampEn), and mean frequency (MF) were used to characterize behavioral strategies. Regional cortical activity and inter-regional connectivity of EEG sub-bands were characterized to infer neural control with relative power and phase-lag index (PLI), respectively.ResultsIn contrast to RE, EA magnified the errors in the visual feedback to twice its size during stabilometer stance. The results showed that EA led to smaller RMS of postural fluctuations with greater SampEn and MF than RE did. Compared with RE, EA altered cortical organizations with greater regional powers in the mid-frontal cluster (theta, 4–7 Hz), occipital cluster (alpha, 8–12 Hz), and left temporal cluster (beta, 13–35 Hz). In terms of the phase-lag index of EEG between electrode pairs, EA significantly reduced long-range prefrontal-parietal and prefrontal-occipital connectivity of the alpha/beta bands, and the right tempo-parietal connectivity of the theta/alpha bands. Alternatively, EA augmented the fronto-centro-parietal connectivity of the theta/alpha bands, along with the right temporo-frontal and temporo-parietal connectivity of the beta band.ConclusionEA alters postural strategies to improve stance stability on a stabilometer with visual feedback, attributable to enhanced error processing and attentional release for target localization. This study provides supporting neural correlates for the use of virtual reality with EA during balance training.

Multifractal roots of suprapostural dexterity.

Visually guided postural control emerges in response to task constraints. Task constraints generate physiological fluctuations that foster the exploration of available sensory information at many scales. Temporally correlated fluctuations quantified using fractal and multifractal metrics have been shown to carry perceptual information across the body. The risk of temporally correlated fluctuations is that stable sway appears to depend on a healthy balance of standard deviation (SD): too much or too little SD entails destabilization of posture. This study presses on the visual guidance of posture by prompting participants to quietly stand and fixate at distances within, less than, and beyond comfortable viewing distance. Manipulations of the visual precision demands associated with fixating nearer and farther than comfortable viewing distance reveals an adaptive relationship between SD and temporal correlations in postural fluctuations. Changing the viewing distance of the fixation target shows that increases in temporal correlations and SD predict subsequent reductions in each other. These findings indicate that the balance of SD within stable bounds may depend on a tendency for temporal correlations to self-correct across time. Notably, these relationships became stronger with greater distance from the most comfortable viewing and reaching distance, suggesting that this self-correcting relationship allows the visual layout to press the postural system into a poise for engaging with objects and events. Incorporating multifractal analysis showed that all effects attributable to monofractal evidence were better attributed to multifractal evidence of nonlinear interactions across scales. These results offer a glimpse of how current nonlinear dynamical models of self-correction may play out in biological goal-oriented behavior. We interpret these findings as part of the growing evidence that multifractal nonlinearity is a modeling strategy that resonates strongly with ecological-psychological approaches to perception and action.

Detection of oriented fractal scaling components in anisotropic two-dimensional trajectories

We propose a novel class of mixed fluctuations with different orientations and fractal scaling features as a model for anisotropic two-dimensional (2D) trajectories hypothesized to appear in complex systems. Furthermore, we develop the oriented fractal scaling component analysis (OFSCA) to decompose such mixed fluctuations into the original orientation components. In the OFSCA, the original orientations are detected based on the principle that the original angles are orthogonal to the angles with the minimum and maximum scaling exponents of the mixed fluctuations. In our approach, the angle-dependent scaling properties are estimated using the Savitzky–Golay-filter-based detrended moving-average analysis (DMA), which has a higher detrending order than the conventional moving-average-filter-based DMA. To illustrate the OFSCA, we demonstrate that the numerically generated time-series of mixed fractional Gaussian noise (fGn) processes with non-orthogonal orientations and different scaling exponents is successfully decomposed into the original fGn components. We demonstrate the existence of oriented components in the 2D trajectories by applying OFSCA to real-world time-series, such as human postural fluctuations during standing and seismic ground acceleration during the great 2011 Tohoku-oki earthquake.

Visual effort moderates postural cascade dynamics

Standing still and focusing on a visible target in front of us is a preamble to many coordinated behaviors (e.g., reaching an object). Hiding behind its apparent simplicity is a deep layering of texture at many scales. The task of standing still laces together activities at multiple scales: from ensuring that a few photoreceptors on the retina cover the target in the visual field on an extremely fine scale to synergies spanning the limbs and joints at smaller scales to the mechanical layout of the ground underfoot and optic flow in the visual field on the coarser scales. Here, we used multiscale probability density function (PDF) analysis to show that postural fluctuations exhibit similar statistical signatures of cascade dynamics as found in fluid flow. In participants asked to stand quietly, the oculomotor strain of visually fixating at different distances moderated postural cascade dynamics. Visually fixating at a comfortable viewing distance elicited posture with a similar cascade dynamics as posture with eyes closed. Greater viewing distances known to stabilize posture showed more diminished cascade dynamics. In contrast, nearest and farthest viewing distances requiring greater oculomotor strain to focus on targets elicited a dramatic strengthening of postural cascade dynamics, reflecting active postural adjustments. Critically, these findings suggest that vision stabilizes posture by reconfiguring the prestressed poise that prepares the body to interact with different spatial layouts.

The Effect of a Six-week Core Stability Exercises on Balance, Strength, and Endurance in Female Students With Trunk Defects

Purpose: Core stability is the ability of the lumbopelvic-hip complex to prevent spinal instability and return to equilibrium after a perturbation. The special physical condition in students and especially the female ones-makes them prone to Trunk Defects (TDs); thus, it makes them prone to numerous injuries, like problems in balance. The present study aimed to examine the effect of Core Stability Exercises (CSEs) on static and dynamic balance, strength, and endurance among female students with TDs. Methods: This was a quasi-experimental study with a pretest-posttest design. The study samples were 30 female high-school students with TDs (Mean±SD age: 15.63±0.49 y, height: 1.60±0.04 m, &amp; weight: 55.96±6.08 kg). All the subjects were placed in the same group. The Star Excursion Balance Test (SEBT) was used to evaluate the dynamic balance; One-Legged Stance Test (OLST) was employed to evaluate the static balance; the McGill test was applied to evaluate trunk endurance; a dynamometer was used to assess the trunk muscle strength, and tuck-jump screening test was implemented to determine students with TDs. These tests were employed at pretest and posttest phases. The research subjects followed CSEs for 6 weeks, 3 sessions per week, and approximately 45 minutes per session, supervised by the researcher. The Dependent Samples t-test at the significance level of P=0.05 was used for data analysis. Results: The present study results indicated a significant difference in strength, muscular endurance, as well as static and dynamic balance in the study subjects after the exercise program (P=0.001). Conclusion: According to the data, 6 weeks of CSEs could provide a solid foundation for the transfer of forces between the limbs. This is achieved by enhancing the strength and endurance of the core muscles of the body; accordingly, it leads to improved static and dynamic balance in female students with trunk control defect by reducing postural fluctuations. However, further extensive studies with larger sample sizes are required for providing more accurate conclusions.

Constraints of Load and Posture on Coordination Variability and Marksmanship Performance.

The purpose of this study was to assess the establishment of dynamic marksmanship performance under different load and postural configurations. Participants quickly established two postures (forward and high targets) under head, trunk, and extremity loads during marksmanship performance. With the dynamic establishment of posture, load disrupted coordinative dynamics, resulting in reduced speed and accuracy on target. Specifically, torso loads increased segmental variability while establishing posture, and smaller head and upper extremity loads extended quieting time before firing. Increased head extension at the high target further destabilized posture, with reduced accuracy across all loads. Large torso loads reduced the adaptability to modulate postural fluctuations at the foot center of pressure while establishing postures for marksmanship, as evidenced by reductions in center of pressure variability. This study expands traditional static marksmanship research, providing insight into relations between task performance, coordinative variability, and postural control while dynamically establishing precision postures.

A preliminary study on the effects of fixation of joint degrees of freedom on postural fluctuation

A preliminary study on the effects of fixation of joint degrees of freedom on postural fluctuation

Robotic finger perturbation training improves finger postural steadiness and hand dexterity

The purpose of the study was to understand the effect of robotic finger perturbation training on steadiness in finger posture and hand dexterity in healthy young adults. A mobile robotic finger training system was designed to have the functions of high-speed mechanical response, two degrees of freedom, and adjustable loading amplitude and direction. Healthy young adults were assigned to one of the three groups: random perturbation training (RPT), constant force training (CFT), and control. Subjects in RPT and CFT performed steady posture training with their index finger using the robot in different modes: random force in RPT and constant force in CFT. After the 2-week intervention period, fluctuations of the index finger posture decreased only in RPT during steady position-matching tasks with an inertial load. Purdue pegboard test score improved also in RPT only. The relative change in finger postural fluctuations was negatively correlated with the relative change in the number of completed pegs in the pegboard test in RPT. The results indicate that finger posture training with random mechanical perturbations of varying amplitudes and directions of force is effective in improving finger postural steadiness and hand dexterity in healthy young adults.

Dynamical analysis of balance in vestibular schwannoma patients

The analysis of the complexity of postural fluctuations is a recent method for assessing postural control. Complexity relates to the irregularity of the center of pressure time series and characterizes the ability of postural control to meet a changing environment. In our study, we used the sample entropy (SampEn) parameter to evaluate the complexity of postural sway velocity time series in patients with vestibular schwannoma (n=19) compared to healthy controls (n=20), using the sensory organization test. Patients performed postural assessments three days before surgical ablation of the tumor, then three times after surgery, at eight, thirty, and ninety days. The control group underwent posturographic tests only once. Our results demonstrated that SampEn values distinguished both groups before surgery only in postural tasks where vestibular afferences significantly contribute to maintaining balance. We also found an immediate decrease of complexity after the surgical resection of the tumor. Our results are in line with the theory of complexity loss of physiological systems stating that reducing the number of their structural components or altering their coupling leads to a decrease in complexity. Finally, our findings showed that progressive restoration of complexity over time was such that no difference was found between the two groups ninety days after surgery, due to the implementation of central adaptive mechanisms and the substitution by other sensory afferences. Thus, the SampEn parameter can highlight the postural effects of vestibular pathology, and complexity analysis appears to be a valuable tool for investigating the temporal structure of CoP time series.

Influence of musical groove on postural sway.

Timescales of postural fluctuation reflect underlying neuromuscular processes in balance control that are influenced by sensory information and the performance of concurrent cognitive and motor tasks. An open question is how postural fluctuations entrain to complex environmental rhythms, such as in music, which also vary on multiple timescales. Musical groove describes the property of music that encourages auditory-motor synchronization and is used to study voluntary motor entrainment to rhythmic sounds. The influence of groove on balance control mechanisms remains unexplored. We recorded fluctuations in center of pressure (CoP) of standing participants (N = 40) listening to low and high groove music and during quiet stance. We found an effect of musical groove on radial sway variability, with the least amount of variability in the high groove condition. In addition, we observed that groove influenced postural sway entrainment at various temporal scales. For example, with increasing levels of groove, we observed more entrainment to shorter, local timescale rhythmic musical occurrences. In contrast, we observed more entrainment to longer, global timescale features of the music, such as periodicity, with decreasing levels of groove. Finally, musical experience influenced the amount of postural variability and entrainment at local and global timescales. We conclude that groove in music and musical experience can influence the neural mechanisms that govern balance control, and discuss implications of our findings in terms of multiscale sensorimotor coupling. (PsycINFO Database Record