There is a fundamental gap in understanding how the cerebral cortex contributes to balance control. Accumulating evidence reveals a strong link between cognitive decline and increased prevalence of falls indicating that the brain plays a meaningful role in controlling balance. However, beyond recognizing this correlation, there remains little mechanistic understanding of what the brain actually does to avoid a fall. This knowledge gap is striking since higher brain processes may offer powerful mechanisms to avoid falls in the cluttered and choice-demanding situations we encounter in daily life. The long-term goal of the proposed research is to understand how higher brain processes help us prevent falls in the complex environments we face every day, and how this changes with age. One important but untested way the brain may help avoid falls is by preparing balance recovery actions by viewing objects in our surroundings. Such a mechanism may help overcome the conflicting motor demands of speed and contextual adaptation, even when a loss of stability is unexpected. The control of balance serves as a critical foundation for autonomy and an active lifestyle. As advances in medical care have prolonged life expectancy, the need to preserve mobility and maintain independence has become an increasing priority for the healthcare system. Falls become more commonplace as we get older and the potential for any given fall leading to serious harm, long term disability or even death increases as we age. The objective in this application is to determine if cortical motor output is modified when viewing objects that may be useful to recover balance and thus avoid a fall. The central hypothesis is that viewing a safety handle will facilitate the motor cortical hand representation relative to conditions where the handle is blocked. Furthermore, the successful ability to navigate the hand to establish a new support base, and thus avoid a fall, will correlate with this pre-set. It is predicted that older adults will show an impaired ability to appropriately modulate motor cortical activity based on visual cues when compared with young adults and this will result in behavioral deficits. The rationale for the proposed research comes from studies in animals and humans demonstrating that viewing objects can potentiate action, a concept known as `affordances.' Advance priming of postural recovery reactions may help us avoid falls, especially in complex response environments where some actions are afforded while others are blocked, and this may occur even before detecting a loss of balance. The hypothesis will be tested by pursuing two specific aims: 1) To determine if motor cortical activity is facilitated by viewing a safety handle and, if so, how this changes with age and 2) To determine if the pre-Supplementary Motor Area of the brain influences motor cortical activity in conflict resolution of compensatory balance actions. This approach is innovative because brain processes will be measured before a disturbance to posture, and then assessed relative to the eventual recovery response. By applying a direct neurophysiological probe (Transcranial Magnetic Stimulation), brain-based mechanisms involved with balance recovery will be revealed. This will extend upon past research limited to external performance measures in the timeframe after perturbation. The proposed research is significant because the present knowledge gap could limit effectiveness of rehabilitation efforts for those with cortical-based risk factors for a fall.
The proposed research is relevant to public health because of the importance of balance control in maintaining an independent, active lifestyle ? key factors in successful aging. This project is relevant to the mission of the National Institute on Aging as it will advance understanding of neural mechanisms in reactive balance control, with an emphasis on how these mechanisms change with age. Given the need to match diagnoses and recovery methods with specific deficits, this improved understanding could increase effectiveness of rehabilitation efforts for those with cortical-based risk factors for a fall.