Postural threat differentially affects the feedforward and feedback components of the vestibular‐evoked balance response

Abstract

Circumstances may render the consequence of falling quite severe, thus maximising the motivation to control postural sway. This commonly occurs when exposed to height and may result from the interaction of many factors, including fear, arousal, sensory information and perception. Here, we examined human vestibular-evoked balance responses during exposure to a highly threatening postural context. Nine subjects stood with eyes closed on a narrow walkway elevated 3.85 m above ground level. This evoked an altered psycho-physiological state, demonstrated by a twofold increase in skin conductance. Balance responses were then evoked by galvanic vestibular stimulation. The sway response, which comprised a whole-body lean in the direction of the edge of the walkway, was significantly and substantially attenuated after ~800 ms. This demonstrates that a strong reason to modify the balance control strategy was created and subjects were highly motivated to minimise sway. Despite this, the initial response remained unchanged. This suggests little effect on the feedforward settings of the nervous system responsible for coupling pure vestibular input to functional motor output. The much stronger, later effect can be attributed to an integration of balance-relevant sensory feedback once the body was in motion. These results demonstrate that the feedforward and feedback components of a vestibular-evoked balance response are differently affected by postural threat. Although a fear of falling has previously been linked with instability and even falling itself, our findings suggest that this relationship is not attributable to changes in the feedforward vestibular control of balance.

The effect of fear of falling on vestibular feedback control of balance

“…This was the same safety system as used by Osler et al. (). As the system was attached to the back of the harness, the ropes ran behind the participant outside their visual field.…”

“…GVS impulses with a current of 1 mA and 2 sec duration were delivered using carbon rubber electrodes (46 by 37 mm) placed in a binaural bipolar configuration similar to the method of Osler et al. (). This type of stimulus has shown to evoke significant body sway responses (Day et al.…”

“…; Osler et al. ). When fearful, movements become more cautious and joint stiffness tends to increase (Adkin et al.…”

“…; Osler et al. ; Young and Mark ). Studies of fall risk in the elderly have shown associations between cognitive motor measures (e.g., concern about falling and poor executive function) and physiological measures of impaired balance (Delbaere et al.…”

Cognitively and socially induced stress affects postural control

“…However, the previous studies assessing emotional contexts in postural control have used both self-report and physiological measures of emotion and arousal. For example, studies assessing postural threat and fear of falling have primarily used electrodermal activity which measures skin conductance, showing that it is a reliable measure of postural threat (Cleworth et al 2012;Osler et al 2013). On the other hand, studies using passive viewing of threatening images used heart rate, based on the idea from the animal literature that freezing is accompanied by bradycardia (Azevedo et al 2005;Hagenaars et al 2012;Roelofs et al 2010).…”