UBC Theses and Dissertations
Fear of falling, proprioception and spinal reflex modulation Davis, Justin Robert
Clinical and experimental research has demonstrated that the emotional experience of fear impairs postural stability in humans. This is problematic considering that fear-related postural instability contributes to a greater likelihood of an individual suffering a fall that can result in devastating physical and financial consequences. For this reason, the research presented in this thesis was performed to clarify the current description of the postural behaviour observed among those who experience fear and/or anxiety and to investigate how human proprioceptive information is utilized by the central nervous system to explain anxiety-induced changes in postural control. Over a series of four consecutive studies, elevated surface heights were used to assess the within-subject effect of fear and anxiety on changes in static posturography, spinal reflex excitability as well as changes in mechanically (TEP) and electrically (SEP) evoked somatosensory potentials. The results of the first study demonstrated that the changes in postural control that occurred with increased surface height were dependent upon the degree of fear of falling experienced by the participants. The results of the second study demonstrated that soleus tendon reflex (STR) excitability could be facilitated during states of height-induced fear and anxiety, without any accompanying changes at the level of the somatosensory cortex. The results of the third study failed to demonstrate that descending pre-synaptic inhibition influences soleus Hoffmann reflex (SOL H-reflex) excitability during states of height-induced fear and anxiety. As such, the fourth study in this thesis was designed to test the effectiveness of using visual feedback to overcome the biomechanical confounds that limited the interpretation of changes in static posturography measures and SOL H-reflex excitability observed in the previous three studies. Taken together, the results of these four studies extend the current understanding of how posture changes during states of height-induced fear and anxiety and sheds new light on the mechanisms that facilitate the changes in spinal reflex excitability and cortical control of posture during such circumstances.
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