Type of auditory cues and apparatus influence how healthy young adults integrate sounds for dynamic balance.

It is unclear whether the brain handles auditory cues similarly to visual cues for balance. We investigated the influence of headphones and loudspeaker reproduction of sounds on dynamic balance performance when an individual is facing a cognitive challenge. Twenty participants (16 females, aged 19-36) were asked to avoid a ball according to a specific visual rule. Visuals were projected from the HTC Vive head-mounted display in an acoustically controlled space. We varied the environment by adding congruent sounds (sounds coincide with the visual rule) or incongruent sounds (sounds may or may not coincide with the visual rule) as well as creating a multimodal (visual and congruent sounds) vs. unimodal (visual or congruent sounds only) display of stimuli. Sounds were played over headphones or loudspeakers. We quantified reaction time (RT) and accuracy (choosing the correct direction to move) by capturing the head movement. We found that in the absence of sounds, RT was slower with headphones compared to loudspeakers, but the introduction of either congruent or incongruent sounds resulted in faster movements with headphones such that RT was no longer different between apparatus. Participants used congruent sounds to improve accuracy but disregarded incongruent sounds. This suggests that selective attention may explain how sounds are incorporated into dynamic balance performance in healthy young adults. Participants leveraged sounds played over loudspeakers, but not over headphones, to enhance accuracy in a unimodal dark environment. This may be explained by the natural listening conditions created by loudspeakers where sounds may be perceived as externalized.

Postural Control under Cognitive Load: Evidence of Increased Automaticity Revealed by Center-of-Pressure and Head Kinematics.

How postural responses change with sensory perturbations while also performing a cognitive task is still debatable. This study investigated this question via comprehensive assessment of postural sway, head kinematics and their coupling. Twenty-three healthy young adults stood in tandem with eyes open or wearing the HTC Vive Head-Mounted Display (HMD) with a static or dynamic (i.e., movement in the anterior-posterior direction at 5 mm or 32 mm at 0.2 Hz) 3-wall stars display. On half of the trials, participants performed a cognitive serial subtraction task. Medio-lateral center-of-pressure (COP) path significantly increased with the cognitive task, particularly with dynamic visuals whereas medio-lateral variance decreased with the cognitive task. Head path and velocity significantly increased with the cognitive task in both directions while variance decreased. Head-COP cross-correlations ranged between 0.78 and 0.66. These findings, accompanied by frequency analysis, suggest that postural control switched to primarily relying on somatosensory input under challenging cognitive load conditions. Several differences between head and COP suggest that head kinematics contribute an important additional facet of postural control and the relationship between head and COP may depend on task and stance position. The potential of HMDs for clinical assessments of balance needs to be further explored.

Factors associated with dynamic balance in people with Persistent Postural Perceptual Dizziness (PPPD): a cross-sectional study using a virtual-reality Four Square Step Test.

BACKGROUND: Persistent postural-perceptual dizziness (PPPD) is a condition characterized by chronic subjective dizziness and exacerbated by visual stimuli or upright movement. Typical balance tests do not replicate the environments known to increase symptoms in people with PPPD-crowded places with moving objects. Using a virtual reality system, we quantified dynamic balance in people with PPPD and healthy controls in diverse visual conditions. METHODS: Twenty-two individuals with PPPD and 29 controls performed a square-shaped fast walking task (Four-Square Step Test Virtual Reality-FSST-VR) using a head-mounted-display (HTC Vive) under 3 visual conditions (empty train platform; people moving; people and trains moving). Head kinematics was used to measure task duration, movement smoothness and anterior-posterior (AP) and medio-lateral (ML) ranges of movement (ROM). Heart rate (HR) was monitored using a chest-band. Participants also completed a functional mobility test (Timed-Up-and-Go; TUG) and questionnaires measuring anxiety (State-Trait Anxiety Inventory; STAI), balance confidence (Activities-Specific Balance Confidence; ABC), perceived disability (Dizziness Handicap Inventory) and simulator sickness (Simulator Sickness Questionnaire). Main effects of visual load and group and associations between performance, functional and self-reported outcomes were examined. RESULTS: State anxiety and simulator sickness did not increase following testing. AP-ROM and HR increased with high visual load in both groups (p < 0.05). There were no significant between-group differences in head kinematics. In the high visual load conditions, high trait anxiety and longer TUG duration were moderately associated with reduced AP and ML-ROM in the PPPD group and low ABC and  high perceived disability were associated with reduced AP-ROM (|r| = 0.47 to 0.53; p < 0.05). In contrast, in controls high STAI-trait, low ABC and longer TUG duration were associated with increased AP-ROM (|r| = 0.38 to 0.46; p < 0.05) and longer TUG duration was associated with increased ML-ROM (r = 0.53, p < 0.01). CONCLUSIONS: FSST-VR may shed light on movement strategies in PPPD beyond task duration. While no main effect of group was observed, the distinct associations with self-reported and functional outcomes, identified using spatial head kinematics, suggest that some people with PPPD reduce head degrees of freedom when performing a dynamic balance task. This supports a potential link between spatial perception and PPPD symptomatology.

People with persistent postural-perceptual dizziness demonstrate altered postural strategies in complex visual and cognitive environments.

BACKGROUND: People with PPPD report imbalance, increase in symptoms and impaired function within complex visual environments, but understanding of the mechanism for these behaviors is still lacking. OBJECTIVE: To investigate postural control in PPPD we compared changes in center of pressure (COP) and head kinematics of people with PPPD (N = 22) and healthy controls (N = 20) in response to different combinations of visual and cognitive perturbations during a challenging balance task. METHODS: Participants stood in a tandem position. Static or moving stars (0.2 Hz, 5 mm or 32 mm amplitude, anterior-posterior direction) were displayed through a head-mounted display (HTC Vive). On half the trials, participants performed a serial-3 subtraction task. We measured medio-lateral and anterior-posterior path and acceleration of COP and head. RESULTS: Controls significantly increased all COP and head parameters with the cognitive task whereas PPPD increased only COP ML path and acceleration. Only controls significantly increased head anterior-posterior & medio-lateral acceleration with moving visual load. Cognitive task performance was similar between groups. CONCLUSIONS: We observed altered postural strategies in people with PPPD, in the form of reduced movement with challenge, particularly around the head segment. The potential of this simple and portable head-mounted display setup for differential diagnosis of vestibular disorders should be further explored.

Auditory Input and Postural Control in Adults: A Narrative Review.

Importance: An increase in the number of mechanistic studies targeting the association between sound and balance has been observed in recent years, but their results appear equivocal. Observations: A search of PubMed and the Cochrane Database of Systematic Reviews for English-language studies on auditory input and postural control published from database inception through October 31, 2019, yielded 28 articles for review. These articles included 18 (64%) studies of healthy adults, 1 (4%) of participants with Alzheimer disease, 2 (7%) of participants with congenital blindness, 3 (11%) of participants with vestibular loss, and 4 (14%) of participants with diverse levels of hearing loss. Studies varied by the type of audio stimuli (natural vs generated sounds), apparatus (speakers vs headphones), and movement of sounds (eg, stationary, rotational). Most balance measurements involved standing on the floor or foam with eyes open or closed during which sway amount or velocity was quantified. Stationary broadband sounds, including white or environmental noise, may improve balance, but the results regarding stationary pure tone were inconclusive. The implication of moving sounds varied by apparatus (typically destabilizing when headphones were used) and sensory loss (more destabilizing with vestibular or hearing loss but perhaps less with a unilateral cochlear implant). Conclusions and Relevance: Findings from this review suggest that stationary broadband noise can serve as an auditory anchor for balance primarily when projected via speakers and when the balance task is challenging. More research is needed that includes individuals with sensory loss and that tests paradigms using dynamic, ecologically valid sounds; clinicians should also consider auditory cues and the presence of hearing loss in balance and fall-risk assessments.

Depressive symptoms may increase the risk of the future development of freezing of gait in patients with Parkinson's disease: Findings from a 5-year prospective study.

INTRODUCTION: Prospective studies identifying predictors of freezing of gait (FOG) in Parkinson's disease (PD) are limited. We aim to explore which symptoms are associated with future development of FOG in non-freezers. METHODS: Fifty-seven PD patients without FOG at baseline were re-evaluated after a mean of five years. At baseline, disease severity [Unified Parkinson's Disease Rating Scale (MDS-UPDRS)], gait under single and dual-tasking, balance, cognition and other non-motor symptoms were assessed. The new-FOG-questionnaire (NFOG-Q) determined FOG. Multivariate binary logistic regression determined independent predictors of FOG. RESULTS: At follow-up, 26 subjects (46%) had FOG while 31 remained non-freezers. At baseline, non-freezers (FOG-) and future freezers (FOG+) were similar (p > 0.10) with respect to age, gender, disease duration, dopaminergic medications, and cognitive function. However, FOG + had significantly worse scores on the Geriatric Depression Scale (GDS) (FOG+:5.2 ± 3.7; FOG-:2.4 ± 2.0, p = 0.005), PDQ-39, the NMS-questionnaire, UPDRS-part I, UPDRS-part III (off), and the Berg Balance Scale. In binary logistic regression, GDS, gait speed and UPDRS-III (on vs. off) were the only significant independent predictors of future FOG (GDS: OR = 10.93, p = 0.003, ΔUPDRS-III: OR = 1.34, p = 0.006). Moreover, 80% of the subjects who had marked depressive symptoms at baseline (GDS≥5) developed FOG at follow-up. In contrast, only 27% of those with few depressive symptoms at baseline became freezers (p < 0.001). CONCLUSIONS: Depressive symptoms apparently precede the development of FOG. While elucidation of the relationship between depression and FOG needs further study, our findings offer another perspective regarding the pathophysiology of FOG and may help clinicians to estimate the risk of developing this debilitating phenomenon.