Neural control of balance in increasingly difficult standing tasks

For almost 150 years, researchers have been intrigued by the complex neural control of standing balance. Despite accumulating evidence showing cortical involvement, much is yet to be learnt about the nuances of how the motor cortex (M1) tunes muscle activation in standing. This thesis examined the neural input to leg muscles in increasingly difficult standing tasks. It was found that the net output from M1 sets the activation of leg muscles and consequently influences postural sway.
This net M1 output is determined by a combination of inhibitory and facilitatory processes which likely account for different aspects of postural control like cognitive influences, planning and preparation for perturbations. Additionally, examination of the synchronized output from the cortex to multiple muscles showed that the cortex favors reciprocal control, which is mechanically advantageous and also costs less energy. Also, such synchronized outputs are tailored to the biomechanical demands of each task. Finally, a preliminary examination of the factors contributing to individual differences in neural control of standing was conducted. Each individual’s intrinsic neural excitability (possibly driven by genetics or plasticity due to previous experiences) influenced how they controlled balance in the increasingly difficult tasks. Additionally, cortical excitability was associated with self-reported balance confidence and likely mediates the effect of this cognitive attribute on motor performance. In conclusion, the findings of this thesis suggest that the cortex plays a role in the higher order planning and processing required for determining muscle activation patterns and maintaining balance in standing.