The effect of ageing on vestibular control of balance

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Falls are a major problem for the elderly. Approximately 30% of people aged over 65 experience one or more falls per year, rising to 50% after 80. 10-15% of falls result in serious injury, costing the NHS and social services up to £1billion annually. This problem can only be exacerbated by an ageing population. Various factors such as muscle weakness and sensory loss have been associated with increased risk of falling, but despite the magnitude of the problem, we know little about mechanisms underlying falls. A structure which is known to play an important role in maintaining balance is the vestibular system, which resides in the inner ear. Vestibular feedback tells us how the head is moving in space and this information is used to reduce postural sway. Vestibular reflexes are therefore important in arresting falls. However, for them to work properly requires the information to be transformed from a head-centred to a body-centred frame of reference. This requires a precise sense of head orientation, and also central neural processing. These factors are known to degrade with age and this may cause inaccurate or absent responses, leading to postural instability and falls. This will be tested by assessing the ability of different age groups to use vestibular information for controlling balance. Electrical stimulation of the vestibular nerve will be used to induce a sensation of head movement. This is a painless technique which produces reliable sway responses in standing subjects. The precision of the sway response will be assessed in young (18-40), middle aged (40-65) and elderly (>65) subjects. This will determine the effect of age upon the ability to use vestibular information for balance. Volunteers will also be assessed for fall risk, using a series of sensory-motor tests, and a questionnaire. This will reveal any link between vestibular control of balance and the risk of falling. Reasons underlying altered vestibular responses will also be investigated. Specifically, the ability to sense head orientation, and the integrity of the peripheral vestibular apparatus, will both be tested. This multi-factorial approach will provide an overall picture, from the reasons underlying altered vestibular control, to the consequences for postural stability and falls. This research has implications for identifying individuals at high risk of falling, and for designing exercise and therapy programmes for reducing risk. This is becoming increasingly important in our ageing population.