The Effects of Anxiety, Ageing, and Neurodegenerative Disease on Visual Reweighting for Postural Control

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonFor most people, the complex mechanisms of sensory reweighting and maintaining balance are effective in maintaining relative automaticity and stability. However, this optimal function can be jeopardized by a range of factors. Ageing, anxiety, changes in attention, and neurodegenerative disease are some of the factors that potentially affect sensory integration for balance. These factors are explored in this thesis over several empirical studies using visual perturbations delivered using virtual reality. First, I examined the effects of ageing and anxiety on the postural response to the erroneous visual experience of self-movement (Study 1). Secondly, I explored these effects in the context of Parkinson’s Disease with Freezing of Gait: a population with impaired non-visual sensory processing and increased anxiety related to motor control (Study 2). The final study attempts to isolate the effects of increased conscious control of movement on visual reweighting to examine the degree to which they account for the results of the previous studies (Study 3). Study 1 found that anxiety appears to relate to increased reliance on vision for balance, but it only partially accounts for greater reliance on vision in older adults. Study 2 found that people with PD+FOG take longer responding to the visual perturbation than healthy age-matched adults, and that freezing severity correlates with longer latency and possibly lower magnitude of response. Finally, Study 3 found no significant effect of increased conscious control of movement on reliance on vision for postural control. Overall, while anxiety does have the potential to increase reliance on visual input, increased visual dependency observed in older adults and people with PD is likely to have different origins, potentially related to physiological changes, rather than increased conscious control of movement. The General Discussion reviews the contribution of these findings to research on sensory integration and postural control, and discusses their implications, and directions for future research