Exploring the role of attention towards balance in chronic dizziness: Development of the Balance Vigilance Questionnaire

Chronic dizziness in older adults: Disrupted sensorimotor EEG beta oscillations during postural instability

OBJECTIVE

Chronic dizziness is common in older adults, yet frequently occurs without a clear cause ('idiopathic dizziness'). Patients experience subjective unsteadiness with minimal objective imbalance, potentially related to small vessel disease. Here we examine the hypothesis that this syndrome is associated with disrupted cortical processing of postural instability.

METHODS

EEG and postural sway were recorded in 33 older adults with chronic, idiopathic dizziness (Age, Mean = 77.3 years, SD = 6.4, 61 % female) and 25 matched controls (Age, Mean = 76.9 years, SD = 6.0, 56 % female). EEG was time-locked to spontaneous instances of postural instability and analysed via time-frequency decomposition.

RESULTS

Significant between-group differences in EEG were observed during the early phase of postural instability (p < 0.05, cluster-corrected). Whilst controls exhibited broadband increase in EEG power across sensorimotor areas, dizzy patients displayed suppressed beta activity (19-24 Hz). Contrary to predictions, these differences did not relate to small vessel disease markers (rs < 0.05, ps > 0.720) but to fear of falling (r = -0.44, p = 0.001).

CONCLUSIONS

Previous work implies that suppressing cortical beta enhances the relay of sensory information. We therefore propose that the modulation in beta EEG observed in patients reflects an anxious, top-down strategy to increase sensitivity to instability, which paradoxically causes persistent feelings of subjective imbalance.

SIGNIFICANCE

These results identify associations between idiopathic dizziness and disrupted sensorimotor beta activation during postural instability. Cortical beta during imbalance may be a possible biomarker of chronic, idiopathic dizziness in older adults and/or fear of falling.

Research Progress on the Potential Pathogenesis of Persistent Postural-Perceptual Dizziness

INTRODUCTION

Persistent postural-perceptual dizziness (PPPD) is the most prevalent chronic functional dizziness in the clinic. Unsteadiness, dizziness, or non-spinning vertigo are the main symptoms of PPPD, and they are typically aggravated by upright posture, active or passive movement, and visual stimulation. The pathogenesis of PPPD remains incompletely understood, and it cannot be attributed to any specific anatomical defect within the vestibular system. Consequently, there is no objective examination method for the disease, and the diagnosis primarily depends on the symptoms of the patient, which lack specificity.

METHODS

To better understand the pathogenesis of PPPD and to aid in the development of novel diagnostic strategies and therapies, we conducted a comprehensive narrative review of the relevant literature. We performed a search for literature in PubMed using the following search phrases: "persistent postural-perceptual dizziness" OR "PPPD" OR "chronic subjective dizziness" OR "functional dizziness" OR "space-motion discomfort" OR "visual vertigo" OR "phobic postural vertigo." The reference list of relevant studies was also screened. The search was limited to publications in English, and the final references were selected based on their relevance to the scope of this review.

RESULTS

This review summarizes recent studies that have investigated the pathogenesis of PPPD. It is traditionally assumed that PPPD may result from altered postural control strategies, cortical integration of threat assessment and spatial orientation, or abnormal integration of multi-sensory information. Recent studies have shown that the brain structure, activity, structural connectivity, and even cerebral perfusion of patients with PPPD differ from those of healthy individuals. Furthermore, PPPD patients are different from healthy individuals in spatial navigation ability, vestibular perception thresholds, central sensitization, and oxidative stress. These findings provide additional anatomical and behavioral insights into the pathogenesis of PPPD, suggesting that PPPD may arise from shifts in the interactions among emotional, visuo-vestibular, and sensorimotor networks.

CONCLUSION

Understanding the complex pathogenesis of PPPD is crucial for the development of novel therapeutics against PPPD. Following the existing findings, our review suggests directions for future research.

A "Conscious" Loss of Balance: Directing Attention to Movement Can Impair the Cortical Response to Postural Perturbations

"Trying too hard" can interfere with skilled movement, such as sports and music playing. Postural control can similarly suffer when conscious attention is directed toward it ("conscious movement processing"; CMP). However, the neural mechanisms through which CMP influences balance remain poorly understood. We explored the effects of CMP on electroencephalographic (EEG) perturbation-evoked cortical responses and subsequent balance performance. Twenty healthy young adults (age = 25.1 ± 5 years; 10 males and 10 females) stood on a force plate-embedded moveable platform while mobile EEG was recorded. Participants completed two blocks of 50 discrete perturbations, containing an even mix of slower (186 mm/s peak velocity) and faster (225 mm/s peak velocity) perturbations. One block was performed under conditions of CMP (i.e., instructions to consciously control balance), while the other was performed under "Control" conditions with no additional instructions. For both slow and fast perturbations, CMP resulted in significantly smaller cortical N1 signals (a perturbation-evoked potential localized to the supplementary motor area) and lower sensorimotor beta EEG activity 200-400 ms postperturbation. Significantly greater peak velocities of the center of pressure (i.e., greater postural instability) were also observed during the CMP condition. Our findings provide the first evidence that disruptions to postural control during CMP may be a consequence of insufficient cortical activation relevant for balance (i.e., insufficient cortical N1 responses followed by enhanced beta suppression). We propose that conscious attempts to minimize postural instability through CMP acts as a cognitive dual-task that dampens the sensitivity of the sensorimotor system for future losses of balance.

Cognition in vestibular disorders: state of the field, challenges, and priorities for the future

Vestibular disorders are prevalent and debilitating conditions of the inner ear and brain which affect balance, coordination, and the integration of multisensory inputs. A growing body of research has linked vestibular disorders to cognitive problems, most notably attention, visuospatial perception, spatial memory, and executive function. However, the mechanistic bases of these cognitive sequelae remain poorly defined, and there is a gap between our theoretical understanding of vestibular cognitive dysfunction, and how best to identify and manage this within clinical practice. This article takes stock of these shortcomings and provides recommendations and priorities for healthcare professionals who assess and treat vestibular disorders, and for researchers developing cognitive models and rehabilitation interventions. We highlight the importance of multidisciplinary collaboration for developing and evaluating clinically relevant theoretical models of vestibular cognition, to advance research and treatment.