Balance control and anti-gravity muscle activity during the experience of fear at heights

Abstract

Fear of heights occurs when a visual stimulus causes the apprehension of losing balance and falling. A moderate form of visual height intolerance (vHI) affects about one third of the general population and has relevant consequences for the quality of life. A quantitative evaluation of balance mechanisms in persons susceptible to vHI during height exposure is missing. VHI‐related changes in postural control were assessed by center‐of‐pressure displacements and electromyographic recordings of selected leg, arm, and neck muscles in 16 subjects with vHI while standing at heights on an emergency balcony versus standing in the laboratory at ground level. Characteristics of open‐ and closed‐loop postural control were analyzed. Body sway and muscle activity parameters were correlated with the subjective estimates of fear at heights. During height exposure, (1) open‐loop control was disturbed by a higher diffusion activity (P < 0.001) and (2) the sensory feedback threshold for closed‐loop control was lowered (P < 0.010). Altered postural control was predominantly associated with increased co‐contraction of leg muscles. Body sway and leg and neck muscle co‐contraction correlated with the severity of subjective anxiety (P < 0.050). Alterations in postural control diminished if there were nearby stationary contrasts in the visual surrounding or if subjects stood with eyes closed. The performance of a cognitive dual task also improved impaired balance. Visual heights have two behavioral effects in vHI subjects: A change occurs in (1) open‐ and closed‐loop postural control strategy and (2) co‐contraction of anti‐gravity leg and neck muscles, both of which depend on the severity of evoked fear at heights.

Cortical alterations in phobic postural vertigo – a multimodal imaging approach

“…These findings are complemented by results from posturographic studies and gait analyses in PPV patients, for they show a typical abnormal strategy for postural control of stance and gait . The constant co‐contraction of the anti‐gravity muscles during normal stance in PVV patients seems to be an expression of the irrational fear of imbalance, also observed in specific phobias . It seems likely that the increase in primary motor cortex structure and connectivity with prefrontal areas reflects the predominant cognitive control of stance and gait.…”

Fear of heights freezes gaze to the horizon

“…Visual information about body sway becomes less pronounced with increasing distance to the visual surround [5], until visual feedback completely vanishes at a distance of about 20 meters. A recent study of balance control and antigravity muscle activity during the experience of fear of heights showed that alterations in postural sway diminished if there were nearby stationary contrasts in the visual surroundings (looking down with head flexed), or if subjects stood with eyes closed [30]. A recent study of balance control and antigravity muscle activity during the experience of fear of heights showed that alterations in postural sway diminished if there were nearby stationary contrasts in the visual surroundings (looking down with head flexed), or if subjects stood with eyes closed [30].…”

Quantification of gait changes in subjects with visual height intolerance when exposed to heights

“…This assumption is based on earlier findings that postural imbalance at heights originates from a mismatch between the perception of self-motion relative to the surrounding environment when the distance between the nearest visible objects and the eyes reaches a critical threshold (Brandt et al, 1980 ; Salassa and Zapala, 2009 ). Accordingly, both, subjects unsusceptible to vHI (Bles et al, 1980 ) and subjects susceptible to vHI (Wuehr et al, 2014 ) presented an improved postural stabilization under height exposure when nearby stationary contrasts were present in their visual field. The distance to the surrounding at heights is dependent on the head position and the direction of the gaze in space.…”

“…Compensation strategies might be represented in the findings of Kugler et al; they reported subjects susceptible to vHI having a reduced visual exploration behavior and a frozen gaze in the straight ahead direction with intermittent fast eye movements toward the ground while walking on a high balcony (Kugler et al, 2014 ). In addition to an impaired visual exploration, an anxiety-driven motor program is thought to be triggered by the height stimulus that intensifies attention on body sway and muscle co-contraction, a process that may contribute to the impaired postural control (Brandt and Huppert, 2014 ; Wuehr et al, 2014 ).…”