Postural control in persons with multiple sclerosis: an investigation of dual task cost and physical modeling

Postural control is an essential activity of everyday life. There is ongoing debate concerning the contribution of central and peripheral control processes to the control of upright stance. Multiple sclerosis is known to negatively influence both central and peripheral control processes. This work investigates how human postural control is affected in persons with multiple sclerosis (MS). The first study investigated the cognitive component of postural control in persons with MS. An experimental study was conducted to measure sway parameters during quiet standing and sway parameters during standing while performing a cognitive task. This study included persons with MS with varying levels of disability. It was hypothesized that the persons with higher disability would show a greater difference between the two testing conditions (quiet and dual task) than the persons with lower disability. Although significant differences were found in the traditional sway parameters between the quiet and dual task conditions, the hypothesized interaction between disability and dual task cost was not found. There are many possibilities for why this interaction did not exist. The most likely possibility is a difference in the way the persons with varying levels of disability allocate neurological cognitive resources to the different tasks. Understanding the influence of a cognitive task on postural control will help to further elucidate the factors that contribute to postural control, especially in persons with decreased postural control due to illness where improved postural control is a therapeutic goal. The second study investigates a bi-planar inverted pendulum model of postural control for persons with MS with high and low spasticity. The inverted pendulum model was used to determine the underlying differences in the control strategies of a group of healthy adults compared to a group of persons with MS who have symptomatic spasticity. The model was modified from previous work [1, 2] to incorporate components that could account for the spasticity seen in persons with MS. The MS and controls models were able to create realistic center of pressure (COP) data that had similar traditional COP parameter values to that of experimental data [3]. The model gains used to achieve the realistic COP measures were compared between the controls and MS models. The gains indicated an increased stiffness (proportional gain) in neurological controller the ML direction, and an increased input noise gain in the ML direction for the MS model with high spasticity compared to the controls. These significant differences in the gains that drive the models suggest that there are different control strategies used for persons with MS and controls to maintain postural control. Relating these model gains to physiological components of postural control can help to gain insight into the changes that take place in the postural control system with diseas