Texture perception at the foot sole: comparison between walking, sitting, and to the hand.

We frequently interact with textured surfaces with both our feet and hands. Like texture's importance for grasping, texture perception via the foot sole might provide important signals about the stability of a surface, aiding in maintaining balance. However, how textures are perceived by the foot, and especially under the high forces experienced during walking, is unknown. The current study builds on extensive research investigating texture perception at the hand by presenting everyday textures to the foot while stepping onto them, exploring them with the foot while sitting, and exploring them with the hand. Participants rated each texture along three perceptual dimensions: roughness, hardness, and stickiness. Participants also rated how stable their posture felt when standing upon each texture. Results show that perceptual ratings of each textural dimension were highly correlated across conditions. Hardness exhibited the greatest consistency and stickiness the weakest. Moreover, correlations between stepping and exploration with the foot were lower than those between exploration with the foot and exploration with the hand, suggesting that mode of interaction (high vs. low force) impacts perception more than body region used (foot vs. hand). On an individual level, correlations between conditions were higher than those between participants, suggesting that differences are greater between individuals than between mode of interaction or body region. When investigating the relationship to perceived stability, only hardness contributed significantly, with harder surfaces rated as more stable. Overall, tactile perception appears consistent across body regions and interaction modes, although differences in perception are greater during walking.NEW & NOTEWORTHY We frequently interact with textured surfaces using our feet, but little is known about how textures on the foot sole are perceived as compared with the hand. Here, we show that roughness, hardness, and stickiness ratings are broadly consistent when stepping on textures, exploring them with the foot sole, or with the hand. Hardness also contributes to perceived stability.

The influence of postural threat-induced anxiety on locomotor learning and updating.

The ability to adapt our locomotion in a feedforward (i.e., "predictive") manner is crucial for safe and efficient walking behavior. Equally important is the ability to quickly deadapt and update behavior that is no longer appropriate for the given context. It has been suggested that anxiety induced via postural threat may play a fundamental role in disrupting such deadaptation. We tested this hypothesis, using the "broken escalator" phenomenon: Fifty-six healthy young adults walked onto a stationary walkway ("BEFORE" condition, 5 trials), then onto a moving walkway akin to an airport travelator ("MOVING" condition, 10 trials), and then again onto the stationary walkway ("AFTER" condition, 5 trials). Participants completed all trials while wearing a virtual reality headset, which was used to induce postural threat-related anxiety (raised clifflike drop at the end of the walkway) during different phases of the paradigm. We found that performing the locomotor adaptation phase in a state of increased threat disrupted subsequent deadaptation during AFTER trials: These participants displayed anticipatory muscular activity as if expecting the platform to move and exhibited inappropriate anticipatory forward trunk movement that persisted during multiple AFTER trials. In contrast, postural threat induced during AFTER trials did not affect behavioral or neurophysiological outcomes. These findings highlight that actions learned in the presence of postural threat-induced anxiety are strengthened, leading to difficulties in deadapting these behaviors when no longer appropriate. Given the associations between anxiety and persistent maladaptive gait behaviors (e.g., "overly cautious" gait, functional gait disorders), the findings have implications for the understanding of such conditions.NEW & NOTEWORTHY Safe and efficient locomotion frequently requires movements to be adapted in a feedforward (i.e., "predictive") manner. These adaptations are not always correct, and thus inappropriate behavior must be quickly updated. Here we showed that increased threat disrupts this process. We found that locomotor actions learned in the presence of postural threat-induced anxiety are strengthened, subsequently impairing one's ability to update (or "deadapt") these actions when they are no longer appropriate for the current context.

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

BACKGROUND AND PURPOSE: Vigilance towards balance has been proposed to underpin various chronic dizziness disorders, including persistent postural-perceptual dizziness (PPPD). The objective of this study was to develop (through patient input) a validated balance-specific measure of vigilance that comprehensively assesses the varied ways in which this construct may manifest. METHODS: We developed the Balance Vigilance Questionnaire (Balance-VQ) through patient and clinician feedback, designed to assess vigilance towards balance. We then validated the questionnaire in 497 participants consisting of patients diagnosed with chronic dizziness disorders (including 97 individuals diagnosed with PPPD) and healthy controls. RESULTS: The final six-item Balance-VQ was shown to be a valid and reliable way to assess vigilance towards balance. Scores were significantly higher in individuals diagnosed with PPPD compared to controls. Although scores were also higher in the PPPD group compared to individuals with diagnosed vestibular disorders other than PPPD, Balance-VQ scores did not discriminate between the two groups when confounding factors (including dizziness severity) were controlled for. Scores did, however, independently discriminate between the PPPD group and individuals who experience dizziness in daily life, but who have not been diagnosed with a neuro-otological disorder. CONCLUSIONS: Our findings confirm that the Balance-VQ is a valid and reliable instrument for assessing vigilance towards balance. As symptom vigilance has been identified as a key risk factor for developing chronic dizziness following acute vestibular symptoms or balance disruption, we recommend using the Balance-VQ as a screening tool in people presenting with such symptoms.

Dissociated cerebellar contributions to feedforward gait adaptation.

The cerebellum is important for motor adaptation. Lesions to the vestibulo-cerebellum selectively cause gait ataxia. Here we investigate how such damage affects locomotor adaptation when performing the 'broken escalator' paradigm. Following an auditory cue, participants were required to step from the fixed surface onto a moving platform (akin to an airport travellator). The experiment included three conditions: 10 stationary (BEFORE), 15 moving (MOVING) and 10 stationary (AFTER) trials. We assessed both behavioural (gait approach velocity and trunk sway after stepping onto the moving platform) and neuromuscular outcomes (lower leg muscle activity, EMG). Unlike controls, cerebellar patients showed reduced after-effects (AFTER trials) with respect to gait approach velocity and leg EMG activity. However, patients with cerebellar damage maintain the ability to learn the trunk movement required to maximise stability after stepping onto the moving platform (i.e., reactive postural behaviours). Importantly, our findings reveal that these patients could even initiate these behaviours in a feedforward manner, leading to an after-effect. These findings reveal that the cerebellum is crucial for feedforward locomotor control, but that adaptive locomotor behaviours learned via feedback (i.e., reactive) mechanisms may be preserved following cerebellum damage.

Association between dizziness and future falls and fall-related injuries in older adults: a systematic review and meta-analysis.

BACKGROUND: Dizziness is common in older adults, especially in those attending falls services. Yet, the extent to which dizziness is associated with future falls has not been reviewed. This systematic review and meta-analysis assessed the association between dizziness and future falls and related injuries in older adults. METHODS: EMBASE, CINAHL Plus, SCOPUS and PsycINFO databases were searched from inception to 5 February 2024. The review was registered on PROSPERO (registration ID: CRD42022371839). Meta-analyses were conducted for the associations of dizziness with future falls (including recurrent and injurious falls). Three meta-analyses were performed on different outcomes: any-type falls (≥1 falls), recurrent falls (≥2 falls) and injurious falls. RESULTS: Twenty-nine articles were included in the systematic review (N = 103 306 participants). In a meta-analysis of 14 articles (N = 46 795 participants), dizziness was associated with significantly higher odds of any-type future falls (OR = 1.63, 95% CI = 1.44-1.84). In another meta-analysis involving seven articles (N = 5630 participants), individuals with dizziness also had significantly higher odds of future recurrent falls (OR = 1.98, 95% CI = 1.62-2.42). For both meta-analyses, significant overall associations were observed even when adjusted for important confounding variables. In contrast, a meta-analysis (three articles, N = 46 631 participants) revealed a lack of significant association between dizziness and future injurious falls (OR = 1.12, 95% CI = 0.87-1.45). CONCLUSIONS: Dizziness is an independent predictor of future falls in older adults. These findings emphasise the importance of recognising dizziness as a risk factor for falls and implementing appropriate interventions.

Validating the Breathing Vigilance Questionnaire for use in dysfunctional breathing.

BACKGROUND: Dysfunctional breathing is common among people with and without primary respiratory pathology. While anxiety can contribute to dysfunctional breathing, the underpinning mechanism is unclear. One explanation is that anxiety induces conscious, vigilant monitoring of breathing, disrupting "automatic" breathing mechanics. We validated a new tool that quantifies such breathing-related "vigilance": the Breathing Vigilance Questionnaire (Breathe-VQ). METHODS: 323 healthy adults (mean (range) age 27.3 (18-71) years; 161 males) were analysed. We developed an initial Breathe-VQ (11 items, 1-5 Likert scale) based on the Pain Vigilance and Awareness Scale, using feedback from the target population and clinicians. At baseline, participants completed the Breathe-VQ, Nijmegen Questionnaire (NQ), State-Trait Anxiety Inventory form 2 and Movement-Specific Reinvestment Scale (assessing general conscious processing). 83 people repeated the Breathe-VQ 3 weeks later. RESULTS: Five items were removed based on item-level analysis. The resulting six-item Breathe-VQ questionnaire (score range 6-30) has excellent internal (α=0.892) and test-retest reliability (intraclass correlation 0.810), a minimal detectable change of 6.5 and no floor/ceiling effects. Validity was evidenced by significant positive correlations with trait anxiety and conscious processing scores (r=0.35-0.46). Participants at high risk of having dysfunctional breathing (NQ >23; n=76) had significantly higher Breathe-VQ score (mean±sd 19.1±5.0) than low-risk peers (n=225; mean±sd 13.8±5.4; p<0.001). In this "high risk of dysfunctional breathing" group, Breathe-VQ and NQ scores were significantly associated (p=0.005), even when controlling for risk factors (e.g. trait anxiety). CONCLUSIONS: The Breathe-VQ is a valid and reliable tool to measure breathing vigilance. High breathing vigilance may contribute to dysfunctional breathing and could represent a therapeutic target. Further research is warranted to test Breathe-VQ's prognostic value and assess intervention effects.

The perceived control model of falling: developing a unified framework to understand and assess maladaptive fear of falling.

BACKGROUND: fear of falling is common in older adults and can have a profound influence on a variety of behaviours that increase fall risk. However, fear of falling can also have potentially positive outcomes for certain individuals. Without progressing our understanding of mechanisms underlying these contrasting outcomes, it is difficult to clinically manage fear of falling. METHODS: this paper first summarises recent findings on the topic of fear of falling, balance and fall risk-including work highlighting the protective effects of fear. Specific focus is placed on describing how fear of falling influences perceptual, cognitive and motor process in ways that might either increase or reduce fall risk. Finally, it reports the development and validation of a new clinical tool that can be used to assess the maladaptive components of fear of falling. RESULTS: we present a new conceptual framework-the Perceived Control Model of Falling-that describes specific mechanisms through which fear of falling can influence fall risk. The key conceptual advance is the identification of perceived control over situations that threaten one's balance as the crucial factor mediating the relationship between fear and increased fall risk. The new 4-item scale that we develop-the Updated Perceived Control over Falling Scale (UP-COF)-is a valid and reliable tool to clinically assess perceived control. CONCLUSION: this new conceptualisation and tool (UP-COF) allows clinicians to identify individuals for whom fear of falling is likely to increase fall risk, and target specific underlying maladaptive processes such as low perceived control.

We should be screening for benign paroxysmal positional vertigo (BPPV) in all older adults at risk of falling: a commentary on the World Falls Guidelines.

Benign paroxysmal positional vertigo (BPPV) is amongst the commonest causes of dizziness and falls in older adults. Diagnosing and treating BPPV can reduce falls, and thereby reduce fall-related morbidity and mortality. Recent World Falls Guidelines recommend formal assessment for BPPV in older adults at risk of falling, but only if they report vertigo. However, this recommendation ignores the data that (i) many older adults with BPPV experience dizziness as vague unsteadiness (rather than vertigo), and (ii) others may experience no symptoms of dizziness at all. BPPV without vertigo is due to an impaired vestibular perception of self-motion, termed 'vestibular agnosia'. Vestibular agnosia is found in ageing, neurodegeneration and traumatic brain injury, and results in dramatically increased missed BPPV diagnoses. Patients with BPPV without vertigo are typically the most vulnerable for negative outcomes associated with this disorder. We thus recommend simplifying the World Falls Guidelines: all older adults (>60 years) with objective or subjective balance problems, irrespective of symptomatic complaint, should have positional testing to examine for BPPV.

Protective or harmful? A qualitative exploration of older people's perceptions of worries about falling.

BACKGROUND: worries about falling are common in older people. It has been suggested that these worries can reduce balance safety by acting as a distracting dual-task. However, it is also possible that worries may serve a protective purpose. The present work adopted a qualitative approach to conduct an in-depth exploration of older people's experiences of worries about falling. METHODS: semi-structured interviews were conducted with 17 community-dwelling older people (mean age = 79 years; males = 5/17) who reported experiencing worries about falling. Reflexive thematic analysis was used to analyse the data. RESULTS: experiencing a fall-or otherwise recognising one's balance limitations-brought the physical realities of participants' ageing bodies to the forefront of their awareness. This led to the recognition of their susceptibility for an injurious fall, which triggered worries about falling in situations that threatened their balance. When preventing the subject of their worries (i.e. an injurious fall) was perceived to be within the individual's locus of control, worries led to protective adaptations to behaviour. In contrast, when the subject of their worries was perceived to be outside their control, worries triggered feelings of panic-leading to unhelpful changes in behaviour. CONCLUSION: these findings provide novel insight into the development and consequences of worries about falling in older people. They highlight the importance of considering an individual's perception of control before deciding to clinically intervene to reduce worries about falling.

The relationship between clinical measures of cognitive function and grip strength in healthy older adults.

BACKGROUND: Handgrip strength is considered a surrogate for musculoskeletal strength, however there is emerging evidence of an association with cognition. The specific neurocognitive attribute which best associates with grip strength is unknown. METHODS: We performed a secondary analysis on baseline data in 49 healthy older adults. Grip strength was corrected for body mass index. Control independent variables included age, Montreal Cognitive Assessment, and Trails B. Experimental variables included a clinical measure of simple reaction time, and clinical and computerized go/no-go tasks. The clinical Go/No-Go measure was determined with ReacStick, a rod-shaped device which - when released by the examiner - requires the participant to decide within 390 ms whether to catch the device or let it fall to the ground. RESULTS: Bivariate analysis demonstrated that age and all cognitive measures other than the computer go/no-go response accuracy related to grip strength. Multivariate analyses showed that following inclusion of the control variables, only ReacStick measures (reaction accuracy/simple reaction time) significantly predicted grip strength, explaining an additional 15.90% variance (p = 0.026). In contrast, computerized Go/No-Go accuracy (p = 0.391), response time variability (p = 0.463), and the control variables (p value range = 0.566-0.942) did not predict grip strength. CONCLUSION: A short latency (< 390 ms) visuomotor Go/No-Go task independently predicted over 15% of grip strength variance, whereas a slower screen-based Go/No-Go task did not. These findings support the notion that declining grip strength likely reflects sub-clinical brain changes as well as musculoskeletal dysfunction, possibly explaining the potent relationships between grip strength, disability, chronic disease, and mortality.

Short-latency inhibition mitigates the relationship between conscious movement processing and overly cautious gait.

BACKGROUND: Overly cautious gait is common in older adults. This is characterised by excessively slow gait, shortened steps, broadened base of support and increased double limb support. The current study sought to (1) evaluate if overly cautious gait is associated with attempts to consciously process walking movements, and (2) explore whether an individual's ability to rapidly inhibit a dominant motor response serves to mitigate this relationship. METHODS: A total of 50 older adults walked at a self-selected pace on an instrumented walkway containing two raised wooden obstacles (height = 23 cm). Trait conscious movement processing was measured with the Movement-Specific Reinvestment Scale. Short-latency inhibitory function was assessed using a validated electronic go/no-go ruler catch protocol. We used linear regressions to explore the relationship between these variables and gait parameters indicative of overly cautious gait. RESULTS: When controlling for general cognitive function (MoCA), and functional balance (Berg Balance Scale), the interaction between trait conscious movement processing and short-latency inhibition capacity significantly predicted gait velocity, step length and double limb support. Specifically, older adults with higher trait conscious movement processing and poorer inhibition were more likely to exhibit gait characteristics indicative of cautious gait (i.e. reduced velocity, shorter step lengths and increased double limb support). Neither conscious movement processing nor inhibition independently predicted gait performance. CONCLUSION: The combination of excessive movement processing tendencies and poor short-latency inhibitory capacity was associated with dysfunctional or 'overly cautious' gait. It is therefore plausible that improvement in either factor may lead to improved gait and reduced fall risk.

Exploring attentional focus of older adult fallers during heightened postural threat.

OBJECTIVES: Threats to balance, and subsequent increases in fall-related anxiety, can disrupt attentional processing during gait in older adults, leading to behavioral adaptations which may increase fall risk. However, limited research has investigated what changes in attention occur to contribute to these disruptions. The aim of this research was to describe changes in attention that occur during gait when older adults' balance is threatened, while exploring how previous fall history and trait movement reinvestment (conscious monitoring and control of movement) also influence attention. METHODS: Forty older adults reported where they focus their attention when walking during two scenarios: (1) when they are relaxed and there is little risk of falling, and; (2) when their balance is threatened and they are anxious of falling. RESULTS: During the high-threat condition, participants reported greater attention towards movement processes, threats to balance, worries/disturbing thoughts and self-regulatory strategies, with less attention directed towards task-irrelevant thoughts. However, fall history influenced attentional focus, with fallers directing greater attention towards worries/disturbing thoughts. Contrary to predictions, trait movement reinvestment was not associated with attention directed towards movement processes. DISCUSSION: As processing worries/disturbing thoughts will likely reduce attentional resources available for effective postural control, we highlight this as one potential area to target interventions aimed at reducing the likelihood of repeated falling.

Recalibrating disparities in perceived and actual balance abilities in older adults: a mixed-methods evaluation of a novel exergaming intervention.

BACKGROUND: Published reports suggest a disparity between perceived and actual balance abilities, a trait associated with increased fall-risk in older adults. We investigate whether it is possible to 'recalibrate' these disparities using a novel gaming intervention. METHODS: We recruited 26 older adults for a 4-week intervention in which they participated in 8-sessions using a novel gaming intervention designed to provide explicit, augmented feedback related to postural control. Measures of perceived balance abilities (Falls Efficacy Scale-International) and actual postural control (limits of stability) were assessed pre- and post-intervention. We used focus groups to elicit the opinions of participants about how the game may have influenced balance abilities and confidence. RESULTS: A stronger alignment was observed between postural control and perceived balance capabilities post-intervention (i.e., significant correlations between Falls Efficacy Scale-International scores and limits of stability which were not present pre-intervention). Also, significant improvements in measures of postural control were observed, with these improvements confined to the aspects of postural control for which the exergame provided explicit, augmented feedback. Qualitative data revealed that the intervention made participants more "aware" of their balance abilities. CONCLUSIONS: Our results demonstrate that it is possible to recalibrate the perceptions of older adults relating to their balance abilities through a targeted, short-term intervention. We propose that the post-intervention improvements in postural control may have been, in part, the result of this recalibration; with altered perceptions leading to changes in balance performance. Findings support the application of novel interventions aimed at addressing the psychological factors associated with elderly falls.

The influence of false interoceptive feedback on emotional state and balance responses to height-induced postural threat.

Postural threat elicits a robust emotional response (e.g., fear and anxiety about falling), with concomitant modifications in balance. Recent theoretical accounts propose that emotional responses to postural threats are manifested, in part, from the conscious monitoring and appraisal of bodily signals ('interoception'). Here, we empirically probe the role of interoception in shaping emotional responses to a postural threat by experimentally manipulating interoceptive cardiac feedback. Sixty young adults completed a single 60-s trial under the following conditions: Ground (no threat) without heart rate (HR) feedback, followed by Threat (standing on the edge of a raised surface), during which participants received either false heart rate feedback (either slow [n = 20] or fast [n = 20] HR feedback) or no feedback (n = 20). Participants provided with false fast HR feedback during postural threat felt more fearful, reported feeling less stable, and rated the task more difficult than participants who did not receive HR feedback, or those who received false slow HR feedback (Cohen's d effect size = 0.79 - 1.78). However, behavioural responses did not significantly differ across the three groups. When compared to the no HR feedback group, false slow HR feedback did not significantly affect emotional or behavioural responses to the postural threat. These observations provide the first experimental evidence for emerging theoretical accounts describing the role of interoception in the generation of emotional responses to postural threats.

Short-latency reaction time and accuracy are impaired in patients with cirrhosis: An international multicenter retrospective study.

AIM: The inability to quickly react to an external event can lead to an increased risk for accidents (e.g., falls, car crashes) in patients with cirrhosis. The aim of this study was to determine whether a novel clinically feasible measure of simple reaction time (SRT) and reaction accuracy (RA)-a go/no-go task occurring within 400 ms-could differentiate patients with cirrhosis from controls. METHODS: This retrospective study included 160 patients with cirrhosis and 160 controls assessed between January 2010 and October 2022. SRT and RA were evaluated using a ruler drop paradigm and compared using propensity score matching. Factors distinguishing patients with cirrhosis from controls were assessed using logistic regression and receiver operating characteristics curve (ROC) analyses. RESULTS: Propensity score matching identified 112 participants in each group with comparable baseline characteristics. As compared with controls, patients with cirrhosis exhibited significantly prolonged SRT (200 vs. 174 ms; P < 0.001) and diminished total RA (63% vs. 73%; P < 0.001). After adjustment for confounding factors, SRT and RA independently identified patients with cirrhosis. ROC analyses showed that SRT more effectively identified patients with cirrhosis than did the number-connection test/trail-making test-B (area under the curve, 0.87 vs. 0.60; P < 0.001). CONCLUSIONS: Patients with cirrhosis demonstrated impairments in short-latency cognitive function. Given that SRT and RA are associated with balance, falls, and response to perturbation, these parameters may present a task-specific method to identify patients with cirrhosis at high risk of falls and motor vehicle crashes. Geriatr Gerontol Int 2024; 24: 25-31.

Frailty, falls and poor functional mobility predict new onset of activity restriction due to concerns about falling in older adults: a prospective 12-month cohort study.

PURPOSE: Concerns about falling are common in older adults and often cause activity restriction. This can lead to physical deconditioning, falls and social isolation. However, not every concerned older adult will restrict their activities. This 12-month longitudinal study investigated the physical and psychosocial factors that predict the new onset of activity restriction due to concerns about falling in older people. METHODS: Participants were 543 older adults (Mage = 80.3 ± 4.4 years, range: 75-98) who did not report activity restriction due to concerns about falling at Timepoint-1 (negative response to the following question: "Do concerns about falling stop you going out-and-about?"). Participants completed a battery of physical and psychological assessments at Timepoint-1. Using binary logistic regression, we then assessed which of these variables predicted whether participants reported having started restricting their activity due to concerns about falling at the 12-month follow-up (Timepoint 2). RESULTS: 10.1% of the sample started to restrict activity due to concerns about falling at Timepoint 2. Three key predictors significantly predicted activity restriction group status at 12-month follow-up: greater frailty at Timepoint-1 (Fried Frailty Index; OR = 1.58, 95% CI 1.09-2.30), experiencing a fall between Timepoint-1 and 2 (OR = 2.22, 95% CI 1.13-4.38) and poorer functional mobility at Timepoint-1 (Timed up and Go; OR = 1.08, 95% CI 1.01-1.15). CONCLUSIONS: Frailty, experiencing a fall and poorer functional mobility all predicted the onset of activity restriction due to concerns about falling. Clinicians working in balance and falls-prevention services should regularly screen for frailty, and patients referred to frailty services should likewise receive tailored treatment to help prevent the development of activity restriction due to concerns about falling.

Vestibular loss disrupts visual reactivity in the alpha EEG rhythm.

The alpha rhythm is a dominant electroencephalographic oscillation relevant to sensory-motor and cognitive function. Alpha oscillations are reactive, being for example enhanced by eye closure, and suppressed following eye opening. The determinants of inter-individual variability in reactivity in the alpha rhythm (e.g. changes with amplitude following eye closure) are not fully understood despite the physiological and clinical applicability of this phenomenon, as indicated by the fact that ageing and neurodegeneration reduce reactivity. Strong interactions between visual and vestibular systems raise the theoretical possibility that the vestibular system plays a role in alpha reactivity. To test this hypothesis, we applied electroencephalography in sitting and standing postures in 15 participants with reduced vestibular function (bilateral vestibulopathy, median age = 70 years, interquartile range = 51-77 years) and 15 age-matched controls. We found participants with reduced vestibular function showed less enhancement of alpha electroencephalography power on eye closure in frontoparietal areas, compared to controls. In participants with reduced vestibular function, video head impulse test gain - as a measure of residual vestibulo-ocular reflex function - correlated with reactivity in alpha power across most of the head. Greater reliance on visual input for spatial orientation ('visual dependence', measured with the rod-and-disc test) correlated with less alpha enhancement on eye closure only in participants with reduced vestibular function, and this was partially moderated by video head impulse test gain. Our results demonstrate for the first time that vestibular function influences alpha reactivity. The results are partly explained by the lack of ascending peripheral vestibular input but also by central reorganisation of processing relevant to visuo-vestibular judgements.

The Effects of Conscious Movement Processing on the Neuromuscular Control of Posture.

Maintaining balance is thought to primarily occur sub-consciously. Occasionally, however, individuals will direct conscious attention towards balance, e.g., in response to a threat to balance. Such conscious movement processing (CMP) increases the reliance on attentional resources and may disrupt balance performance. However, the underlying changes in neuromuscular control remain poorly understood. We investigated the effects of CMP (manipulated using verbal instructions) on neural control of posture in twenty-five adults (11 females, mean age = 23.9, range = 18-33). Participants performed 90-s, bipedal stance balance trials in high- and low-CMP conditions, during both stable (solid surface) and unstable (foam) task conditions. Postural sway amplitude, frequency and complexity were used to assess postural control. Surface EMG was recorded bilaterally from lower leg muscles (Soleus, Tibialis Anterior, Gastrocnemius Medialis, Peroneus Longus) and intermuscular coherence (IMC) was assessed for 12 muscle pairs across four frequency bands. We observed significantly increased sway amplitude, and decreased sway frequency and complexity in the high- compared to the low-CMP conditions. All sway variables increased in the unstable compared to the stable conditions. We observed reduced beta band IMC between several muscle pairs during high- compared to low-CMP, but these findings did not remain significant after controlling for multiple comparisons. Finally, IMC significantly increased in the unstable conditions for most muscle combinations and frequency bands. In all, results tentatively suggest that CMP-induced changes in sway outcomes may be facilitated by reduced beta-band IMC, but these findings need to be replicated before they can be interpreted more conclusively.

Balance capacity influences the effects of conscious movement processing on postural control in older adults.

Older adults rely increasingly on conscious processes to control balance. While this could be in response to age-related declines in balance capacity, it is unclear whether such strategy is adaptive or not. We investigated whether balance capacity modified the effects of conscious movement processing (CMP) on postural control in older adults. Forty-seven older adults (Mage = 74.8, range = 61-88) completed 60-s, narrow-stance balance trials on a force platform, under conditions designed to increase (high-CMP; through movement-monitoring instructions) or reduce conscious processing (low-CMP; distraction task). Balance capacity was operationalised as a composite score of Berg Balance Scale and Timed-up-and-Go. Balance capacity influenced the effects of the CMP manipulation on mediolateral sway amplitude (p = .023). Specifically, it positively associated with sway amplitude during the high-CMP condition (ß = 0.273), but not low-CMP condition (ß = -0.060). In other words, higher balance capacity was associated with increased sway during high-CMP, confirming our hypothesis that CMP does not uniformly negatively impact balance performance. Rather, CMP was maladaptive for those with better balance. Results also indicated that older adults' balance capacity influenced the degree to which they could engage conscious or automatic postural control processes. Specifically, we found that, overall, participants showed reduced mediolateral sway frequency and complexity for the high-CMP vs. low-CMP condition (p's ≤ 0.018), indicating reduced automaticity of balance (as expected). However, these effects were significantly attenuated as balance capacity reduced (i.e., smaller changes in those with lower balance capacity, p's < 0.010). Hence, the ability to readily shift between conscious and automatic modes of postural control seems more constrained as balance becomes worse. Overall, these findings suggest clinicians need to consider older adults' balance capacity when using providing instructions or feedback likely to influence CMP within rehabilitation settings.