Investigating the Effect of Stochastic Resonance on Balance in Persons with Multiple Sclerosis

Abstract

Multiple sclerosis (MS) is a chronic neurological disease that affects the central nervous system. It is associated with balance and mobility impairments which increase the risk of falls. Some interventions to improve balance involve endurance and strength training but may prove to be difficult for those with mobility impairments. Stochastic resonance has been explored as a method to improve balance in populations with somatosensory deficits. The effects of stochastic resonance have not been widely studied in MS. The purpose of the study was to investigate the effects of different types of vibration on sway parameters in persons with MS. The aims of the current study are: 1) to understand how the sensing threshold and linear/non-linear sway parameters of people with MS compared to the healthy old and healthy young on one inch of foam and 2) to investigate the effect of the sub-sensory vibration on linear/non-linear sway parameters in people with MS. The MS participant was in the same age range as the healthy older participants which allowed for a healthy versus disease comparison. The MS participant was compared to the healthy young on foam to understand if using foam as a sensory deficit was comparable to a disease population. It was hypothesized that: 1) MS would exhibit greater center-of-pressure (COP) sway with eyes closed compared to healthy old individuals, 2) sub-sensory vibratory stimulus would improve balance in MS, and 3) healthy young individuals on one inch of foam will display similar sway measures and threshold values to MS. One older adult with MS participated in the study. Data from four healthy older adults and four healthy young adults on one inch of foam were included in the study from a previous pilot study using the same procedure. Each participant stood on a force plate with their eyes closed for the sway trials. Three different types of vibration (placebo, white, and pink) were applied to the feet while standing at 90% of their sensing threshold. Linear (RMS and 95% ellipse) and non-linear (sample entropy) measures were extracted and analyzed using MATLAB. No significant difference was seen in the sensing threshold between the multiple sclerosis participant and healthy older adults. The multiple sclerosis participant demonstrated larger sway variability and unpredictability compared to the healthy older adults and healthy young adults on foam. None of the different types of vibration improved balance of the MS participant. The use of foam for healthy young adult participants is not a representative simulation of severe stages of MS. When looking at the effects of the different colors of noise, there does not appear to be an effect on sway parameters. Using this data, a preliminary conclusion can be made that sub-threshold vibration might not be a suitable intervention for those with severe stages of MS. However, these assumptions will need to be confirmed using a larger sample size.