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Abstract of the Week

December Topic: Postural Threat

December 2, 2021

Lim, S. B., Cleworth, T. W., Horslen, B. C., Blouin, J. S., Inglis, J. T., & Carpenter, M. G. (2017). Postural threat influences vestibular-evoked muscular responses. Journal of neurophysiology, 117(2), 604–611. https://doi.org/10.1152/jn.00712.2016

Standing balance is significantly influenced by postural threat. While this effect has been well established, the underlying mechanisms of the effect are less understood. The involvement of the vestibular system is under current debate, and recent studies that investigated the effects of height-induced postural threat on vestibular-evoked responses provide conflicting results based on kinetic (Horslen BC, Dakin CJ, Inglis JT, Blouin JS, Carpenter MG. J Physiol 592: 3671-3685, 2014) and kinematic (Osler CJ, Tersteeg MC, Reynolds RF, Loram ID. Eur J Neurosci 38: 3239-3247, 2013) data. We examined the effect of threat of perturbation, a different form of postural threat, on coupling (cross-correlation, coherence, and gain) of the vestibulo-muscular relationship in 25 participants who maintained standing balance. In the "No-Threat" conditions, participants stood quietly on a stable surface. In the "Threat" condition, participants' balance was threatened with unpredictable mediolateral support surface tilts. Quiet standing immediately before the surface tilts was compared to an equivalent time from the No-Threat conditions. Surface EMG was recorded from bilateral trunk, hip, and leg muscles. Hip and leg muscles exhibited significant increases in peak cross-correlation amplitudes, coherence, and gain (1.23-2.66×) in the Threat condition compared with No-Threat conditions, and significant correlations were observed between threat-related changes in physiological arousal and medium-latency peak cross-correlation amplitude in medial gastrocnemius (r = 0.408) muscles. These findings show a clear threat effect on vestibular-evoked responses in muscles in the lower body, with less robust effects of threat on trunk muscles. Combined with previous work, the present results can provide insight into observed changes during balance control in threatening situations.

New & noteworthy: This is the first study to show increases in vestibular-evoked responses of the lower body muscles under conditions of increased threat of postural perturbation. While robust findings were observed in hip and leg muscles, less consistent results were found in muscles of the trunk. The present findings provide further support in the ongoing debate for arguments that vestibular-evoked balance responses are influenced by fear and anxiety and explain previous threat-related changes in balance.

PMID: 31219931

Link to Free Article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5288487/

December 10, 2021

Ellmers TJ, Kal EC, Young WR. Consciously processing balance leads to distorted perceptions of instability in older adults. J Neurol. 2021 Apr;268(4):1374-1384. doi: 10.1007/s00415-020-10288-6. Epub 2020 Nov 3.

Background: Persistent dizziness without a clear cause is common in older adults. We explored whether an anxiety-driven preoccupation with consciously processing balance may underpin the distorted perceptions of unsteadiness that characterises 'unexplained' dizziness in older adults.

Methods: We experimentally induced anxiety about losing one's balance (through a postural threat manipulation) in a cohort of asymptomatic older adults and evaluated associated changes in perceived stability, conscious movement processing and postural control. These outcomes were also assessed when performing a distracting cognitive task designed to prevent anxiety-related conscious movement processing, in addition to during baseline conditions (ground level).

Results: Despite a lack of increase in postural sway amplitude (p = 0.316), participants reported reductions in perceived stability during postural threat compared to baseline (p < 0.001). A multiple linear regression revealed that anxiety-related conscious movement processing independently predicted perceptions of instability during this condition (p = 0.006). These changes were accompanied by alterations in postural control previously associated with functional dizziness, namely high-frequency postural sway and disrupted interaction between open- and closed-loop postural control (ps < 0.014). While the distraction task successfully reduced conscious processing (p = 0.012), leading to greater perceived stability (p = 0.010), further increases in both postural sway frequency (p = 0.002) and dominance of closed-loop control (p = 0.029) were observed.

Conclusion: These findings implicate the role of conscious movement processing in the formation of distorted perceptions of unsteadiness, suggesting that such perceptions may be modifiable by reducing an over-reliance on conscious processes to regulate balance.

PMID: 33141249

Link to Free Article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7990754/

December 16, 2021

Cleworth TW, Adkin AL, Allum JHJ, Inglis JT, Chua R, Carpenter MG. Postural Threat Modulates Perceptions of Balance-Related Movement During Support Surface Rotations. Neuroscience. 2019 Apr 15;404:413-422. doi: 10.1016/j.neuroscience.2019.02.011. Epub 2019 Feb 18.

Postural threat decreases center of pressure displacements yet increases the magnitude of movement-related conscious sway perception during quiet standing. It is unknown how these changes influence perception of whole body movement during dynamic stance. The aim of this study was to examine how postural threat influences whole-body movements and conscious perception of these movements during continuous pseudo-random support surface perturbations to stance. Sixteen healthy young adults stood on a moveable platform with their eyes closed for 7 min in a low threat (1.1 m above ground, away from edge) then high threat (3.2 m above ground, near edge) condition. Continuous pseudorandom roll platform rotations (± 4.5°, < 0.5 Hz) evoked large amplitude sway in the medio-lateral (ML) direction. Participants were asked to remain upright and avoid a fall at all times while tracking their ML body movements using a hand-held rotary encoder. Kinematic data was recorded using three markers placed on the upper trunk. Questionnaires assessed anxiety, fear and confidence. Electrodermal activity (EDA) was recorded as an indicator of arousal. Height-induced threat increased fear, anxiety and EDA, and decreased confidence. Trunk sway amplitude remained constant, while tracked movement amplitude increased at height. The gain for perceived to trunk movement was significantly increased at height across frequencies. Threat-related increases in sensitivity of sensory systems related to postural control and changes in cognitive and attention processes may lead to misperceptions of actual movement amplitudes, which may be important when examining increased fall risk in those with a fear of falling.

PMID: 30790669

December 29, 2021

Cleworth, T. W., Allum, J., Luu, M. J., Lea, J., Westerberg, B. W., & Carpenter, M. G. (2020). The Effect of Unilateral Vestibular Loss on Standing Balance During Postural Threat. Otology & neurotology : official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology, 41(7), e945–e951. https://doi.org/10.1097/MAO.0000000000002485

Objective: Vestibular deficit patients have an increased fall risk and fear of falling. Postural threat, known to increase balance-related fear and anxiety, influences vestibular gains during quiet standing in young healthy adults. The current study examined whether there is a similar relationship for peripheral unilateral vestibular loss (UVL) patients in comparison to age-matched healthy controls (HC).

Setting: University laboratory.

Study design: Prospective laboratory study.

Patients and controls: Eleven UVL patients, nine with vestibular neurectomy. Eleven aged-matched HCs.

Main outcome measures: Subjects stood on a hydraulic lift placed at two heights: low (0.8 m, away from the edge) and high (3.2 m, at the edge). Amplitude (root mean square), mean power frequency (MPF), and mean position were analyzed for center of foot pressure (COP) and 90% ranges for angle amplitude and velocity for trunk sway.

Results: Group interactions were strongest for anterior-posterior (AP) COP and trunk pitch angle. AP lean away from the edge was greater in HCs than UVLs. HCs, but not UVLs had a decrease in root mean square AP COP with height. Trunk pitch sway was changed similarly. Both groups had increased trunk pitch velocity at height. Changes with height were less for roll: MPF of lateral COP increased with height for UVLs with no changes for HCs, and trunk roll amplitude decreased for both groups.

Conclusions: This report provides evidence for a differential effect of height induced postural threat on balance control between UVLs and HCs presumably due to the reduced vestibular-spinal gain in UVL subjects.

PMID: 32658112

January Topic: Horizontal Canal BPPV

January 5, 2022

Yu J, Gu Y, Meng G, et al. Nystagmus Parameters of Supine Roll Test Correlates With Prognosis After Repositioning Maneuver in Horizontal Semicircular Canal Benign Paroxysmal Positional Vertigo. Front Neurol. 2021;12:790430. Published 2021 Dec 6. doi:10.3389/fneur.2021.790430

Background: Positional nystagmus induced by supine roll test is characteristic for diagnosing horizontal semicircular canal benign paroxysmal positional vertigo (HC-BPPV). In this study, we aimed to explore the value of nystagmus parameters in by supine roll test (SRT) as prognostic factors in HC-BPPV. 

Methods: We retrospectively analyzed the nystagmus parameters of 813 patients diagnosed with HC-BPPV by the SRT model in the SRM-IV system through video nystagmography. Then we used the computer-controlled canalith repositioning procedure (CCRP) mode for treatment. Based on the outcomes, patients were divided into either the cured group or the resistant group. The 1:1 propensity score matching (PSM) was applied to minimize potential selection bias. Then univariable and multivariable analyses were performed to identify the association of nystagmus parameters and the efficacy of CCRP. 

Results: Among the 813 patients, 99 (12.2%) were classified in the resistant group. The right side of HC-BPPV patients was twice the number of the left side patients (537 vs. 276). PSM is used to pair resistant patients to the cured patients, in which 99 pairs were successfully matched. Results of univariate and multivariate analyses showed that patients in the resistant group have longer latency in the affected side [odds ratio (OR) = 1.231 (1.110-1.366); P < 0.001] and slower slow phase velocity (SPV) in the healthy side [OR = 0.957 (0.917-0.999); P = 0.045]. 

Conclusion: Nystagmus parameters may represent the characteristics of canalith. HC-BPPV patients with a longer latency in the affected side and slower SPV on the healthy side during SRT have a higher risk of HC-BPPV persisting after a single CCRP.

PMID: 34938267

 

January 12, 2022

Choi SY, Oh SW, Kim HJ, Kim JS. Determinants for bedside lateralization of benign paroxysmal positional vertigo involving the horizontal semicircular canal. J Neurol. 2020;267(6):1709-1714. doi:10.1007/s00415-020-09763-x

Objectives: This study aimed to define the factors affecting accuracy of bedside determination of the involved side in HC-BPPV.

Interventions: We developed 44 video clips including the nystagmus induced during supine head-roll test from patients with apogeotropic (n = 23) or geotropic (n = 21) HC-BPPV. The intensity of nystagmus was also quantified using video-oculography. Each video clip was presented twice to 25 participants, 14 medical students, and 11 medical personnel trained in neurology or neurotology, and the participants reported the lesion side using an evaluation sheet after each presentation. From the quantified video-oculographic data, absolute difference and asymmetry (absolute difference divided by the sum) of nystagmus intensity were calculated.

Main outcomes and measures: The accuracy of bedside lateralization of HC-BPPV was 83.5% after the first presentation, and 86.0% after the second presentation, and was not different between the medical students and trained personnel after the second presentation. The accuracy was more closely correlated with the asymmetry than the absolute difference (Spearman's ρ = 0.627, p < 0.001). With a cut-off for the asymmetry at 30.8%, the accuracy was estimated at 93.8% with a sensitivity of 92.9%, and the area under the ROC curve of 0.779.

Conclusions and relevance: The accuracy of bedside lateralization of the affected side is acceptable in HC-BPPV when the nystagmus asymmetry is more than 30%.

Keywords: Benign paroxysmal positional vertigo; Horizontal semicircular canal; Nystagmus; Vertigo.

PMID: 32100125

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