THE VESTIBULAR SYSTEM: ITS ROLE IN POSTURAL CONTROL AND ITS FUNCTIONAL ASSESSMENT USING SPATIAL ORIENTATION
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The vestibular system plays a role in postural control and spatial orientation. Ageing adversely affects vestibular function, postural control and the ability to maintain accurate spatial orientation. Study I investigated the interaction of vestibular input with lower limb somatosensory and visual inputs for head and trunk control during normal walking (NW) and narrow-based walking (NBW) and the effect of age on these interactions. The association of clinically measured functions of the vestibular system, lower limb somatosensation and vision with head/trunk control in the frontal plane during NW and NBW, and the impact of age were also examined. Study II evaluated the inter-trial reliability of three tools which can be used to screen for vestibular dysfunction via assessing spatial orientation, in young and older participants, and their sensitivity of these tools to age-related difference in vestibular function. In Study I, 15 young [25.40(3.56) years, 7 females and 8 males] and 15 older [72.60(5.33) years, 8 females and 7 males] were asked to perform NW and NBW. Vestibular, lower limb somatosensory and visual information was manipulated using galvanic vestibular stimulation, medium density foam and blurring goggles respectively; either concurrently or individually. The variables representing head control were more affected by visual and vestibular manipulation. The variables representing trunk control were more affected by lower limb somatosensory manipulation. Further, trunk roll angle during NW was significantly associated with lower limb vibration sensitivity, indicating the importance of lower limb somatosensory signals for trunk control. Age-related difference was only reflected in head control. In Study II, 15 young [28.27(4.61) years, 7 females and 8 males] and 15 older [75.47(4.42) years, 7 females and 8 males] were asked to perform 6 trials of each of the Fukuda Stepping Test (FST), Triangle Walking Test and Straight Walking Test. Reliability and variability of all the relevant variables in the tests were evaluated. Distance of displacement (DD) in the FST was the only variable that exhibited moderate to high reliability and acceptable variability in both age groups. DD was also significantly higher in the older group, suggesting its sensitivity to potential age-related difference in vestibular function.