Cortical contribution to postural control

Abstract

More detailed knowledge of the cortical elements involved in postural control may allow us to understand complex balance disorders. I first exposed older adults with so-called “idiopathic dizziness” to a dynamic postural task (Chapter 1) and found that postural sway was tightly linked to the subjective report of instability. Perceived instability was greater in patients compared to controls, implying a ‘distorted’ sense of imbalance. Psychological variables have been linked to human postural control. To further explore the role of expectation in postural performance and the perception of stability, healthy young subjects were asked to complete a dynamic postural task after being primed about the upcoming perturbation (Chapter 2). Greater sway and/or higher perceived instability was observed, depending on the priming information given. These findings indicate that expectations could modulate postural control. Subsequently, I sought to explore the potential role of the asymmetrical vestibular cortical network for postural control. Accordingly, healthy young subjects received cathodal transcranial Direct Current Stimulation (tDCS) to the left parietal cortex (Chapter 3). The degree of hemispheric dominance modulated postural control by reducing body sway proportionally to their individual dominance. These results indicate that vestibular parietal areas influence postural control and open research avenues for balance disorders. Finally, I explored the changes in brain activity in patients with bilateral vestibular hypofunction (BVH) (Chapter 4) who had their electric brain activity measured using ElectroEncephaloGraphy (EEG) with eyes open and closed. Patients showed reduced alpha activity enhancement on eye closure, suggesting that the patients’ brains remained aroused even with their eyes closed. Further work will seek to investigate alpha reactivity as a measure of central vestibular compensation. The body of work carried out for this thesis furthers our understanding of the underlying neural areas and processes involved in postural control and helps define the nature of neurological balance disorders.