The ageing sensorimotor control system and falls in the elderly

The ageing sensorimotor control system and falls in the elderly

During ageing, degeneration undergoes at all levels of the sensorimotor system and causes unfavourable consequences, including falls. Falls are the predominant cause of unintentional injuries in the elderly and constitute a significant threat to our ageing societies. While extensive research on falls has been done, the relationship between sensorimotor variability, sensorimotor control and falls in elderly has not been investigated. We hypothesise that both sensory and motor noise increases with age and results in more variable movement. This leads to a higher probability of trips while walking, the main causes of falls in the elderly. My research uses motor and sensory psychophysics and computational modelling to characterise sensorimotor variability across age. I pinpoint specific system changes that cause it. Crucially, the experimental tasks we design and use have shared biomechanics of walking and obstacle avoidance and can, therefore, be referred to observed age-related changes in human locomotion. I show that sensorimotor variability in foot placement increases with age and the degree of increase positively correlates with higher foot placement. Sensory psychophysics indicates that increased sensory noise is one cause underlying more variable movement in ageing. Notably, elderly participants rely more on their vision to judge their own foot’s height compared with the young. This could be related to their impaired proprioception. Thus, the multi-sensory integration strategy shifts with age to compensate for increased sensory noise. By developing and using a simple but powerful cortico-spinal-motor model, I also demonstrate that an increase of motor noise in ageing can well be explained by motor neuron loss in the primary motor cortex. In summary, my results provide a first computational and psychophysics driven investigation into how increased sensory and motor noise can lead to falls in the elderly.

The ageing sensorimotor control system and falls in the elderly