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UBC Theses and Dissertations

The influence of emotional factors on the control of balance studied using threat and repeated threat exposure manipulations Zaback, Martin

Abstract

Postural threat manipulations elicit changes in psychological and autonomic state and standing balance control. However, these changes are often poorly correlated and changes to balance control appear heavily dependent on the task-constraints imposed by the threat. This raises questions as to how fear and related psychological processes impact balance control and what are the neural mechanisms mediating these relationships? The studies of this thesis explored these questions using a repeated threat exposure model. Using this model, psychological and autonomic state could be manipulated within a threatening scenario, thereby decoupling these state-related changes from the threat context. Studies 1 and 2 investigated how standing balance control changed as individuals were repeatedly exposed to a height-related postural threat. These studies demonstrated clear dissociations between specific changes in standing balance control and individuals’ psychological and autonomic response to the threat. Specifically, threat-related increases in high-frequency centre of pressure power and plantar/dorsiflexor coactivation demonstrated clear habituation, while more protective components of the response to threat, such as the posterior lean and reduction in low frequency COP power, were invariant. Study 3 demonstrated that low levels of anxiety and arousal in the absence of any overt threat were sufficient to influence distinct components of standing balance control. However, these changes in behaviour did not mirror what is typically seen with a height-related postural threat. Studies 4 and 5 investigated how descending input from cortical and subcortical networks might contribute to the changes in standing balance control observed in studies 1 and 2. Corticospinal and subcortical drive to the soleus, inferred from estimates corticomuscular and intermuscular coherence, were both facilitated by height-related postural threat. However, only corticospinal drive habituated with repeated threat exposure. Cortical potentials time-locked to discrete postural events were facilitated by height-related postural threat, but did not habituate with repeated threat exposure. This thesis demonstrates that only a subset of threat-related changes to standing balance control are tightly coupled with the psychological and autonomic state changes induced by the threat, while others appear largely context dependent. This thesis also provides insight into separate cortical mechanisms which may mediate distinct aspects of this behaviour.

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