Threat effects on human oculo-motor function

Reflexive and volitional saccadic eye movements and their changes in age and progressive supranuclear palsy

BACKGROUND AND OBJECTIVES

Saccades, rapid movements of the eyes towards a visual or remembered target, are useful in understanding the healthy brain and the pathology of neurological conditions such as progressive supranuclear palsy (PSP). We set out to investigate the parameters of horizontal reflexive and volitional saccades, both visually guided and memory-guided, over a 1 min epoch in healthy individuals and PSP patients.

METHODS

An experimental paradigm tested reflexive, volitional visually guided, and volitional memory-guided saccades in young healthy controls (n = 14; 20-31 years), PSP patients (n = 11; 46-75 years) and older age-matched healthy controls (n = 6; 56-71 years). The accuracy and velocity of saccades was recorded using an EyeBrain T2® video eye tracker and analyses performed using the MyEyeAnalysis® software. Two-way analysis of variance (ANOVA) was used to identify significant effects (p < 0.01) between young and older controls to investigate the effects of ageing upon saccades, and between PSP patients and age-matched controls to study the effects of PSP upon saccades.

RESULTS

In both healthy individuals and PSP patients, volitional saccades are slower and less accurate than reflexive saccades. In PSP patients, accuracy is lower across all saccade types compared to age-matched controls, but velocity is lower only for reflexive saccades. Crucially, there is no change in accuracy or velocity of consecutive saccades over short (one-minute) timescales in controls or PSP patients.

CONCLUSIONS

Velocity and accuracy of saccades in PSP does not decrease over one-minute timescales, contrary to that previously observed in Parkinson's Disease (PD), suggesting a potential clinical biomarker for the distinction of PSP from PD.

The Effect of Unilateral Vestibular Loss on Standing Balance During Postural Threat

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.

Assessment of visual sensation, psychiatric profile and quality of life following vestibular schwannoma surgery in patients prehabituated by chemical vestibular ablation

AIMS

Preoperative chemical vestibular ablation can reduce vestibular symptoms in patients who have gone through vestibular schwannoma resection. The goal of this study was to determine whether chemical vestibular prehabituation influences the patients' post-operative perception of visual stimulation, mental status and quality of life. We also tried to find out whether increases of optokinetic nystagmus, measured by routine electronystagmography, correlate with subjective symptoms.

METHODS

We preoperatively administered (2 months prior to surgery) 0.5 - 1.0 mL of 40 mg/mL nonbuffered gentamicin in three intratympanic instillations in 11 patients. Head impulse and caloric tests confirmed reduction of vestibular function in all patients. The control group consisted of 21 patients. Quality of life in both groups was evaluated using the Glasgow Benefit Inventory, the Glasgow Health Status Inventory and the Dizziness Handicap Inventory questionnaires. Visual symptoms and optokinetic sensation were evaluated using a specific questionnaire developed by our team and by measuring gains preoperatively and postoperatively in both groups using routine electronystagmography. The psychological profile was evaluated using the Zung Self-Rating Depression Scale and the Generalised Anxiety Disorder Assessment questionnaires.

RESULTS

There were no statistically significant differences between both groups with regards to the results of the questionnaires. Patients who received preoperative gentamicin were less sensitive to visual stimulation (P<0.10) and many of them had a significantly higher gain in the optokinetic nystagmus than the control group in the preoperative stage.

CONCLUSION

Pre-treatment with gentamicin helps to lower anxiety levels in patients and improves their general postoperative status. Pre-treated patients are also less sensitive to optokinetic stimulation.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03638310.

New Insights on Emotional Contributions to Human Postural Control

It has been just over 20 years since the effects of height-induced threat on human postural control were first investigated. Raising the height of the support surface on which individuals stood increased the perceived consequences of instability and generated postural control changes. Since this initial work, converging evidence has accumulated supporting the efficacy of using height-induced threat to study the effects of emotions on postural control and confirming a direct influence of threat-related changes in arousal, anxiety, and fear of falling on all aspects of postural control, including standing, anticipatory, and reactive balance. In general, threat-related postural changes promote a greater physical safety margin while maintaining upright stance. We use the static balance literature to critically examine the current state of knowledge regarding: (1) the extent to which threat-related changes in postural control are sensitive to threat-related changes in emotions; (2) the underlying neurophysiological and cognitive mechanisms that may contribute to explaining the relationship between emotions and postural control; and (3) the generalizability of threat-related changes across different populations and types of threat. These findings have important implications for understanding the neuromechanisms that control healthy balance, and highlight the need to recognize the potential contributions of psychological and physiological factors to balance deficits associated with age or pathology. We conclude with a discussion of the practical significance of this research, its impact on improving diagnosis and treatment of postural control deficits, and potential directions for future research.