Adaptation in motor strategies for postural control associated with sensory reweighting

The purpose of this study was to identify and differentiate the motor strategies associated with sensory reweighting adapted during specific sensory integration tasks by healthy young adults. Thirty-six subjects (age range: 21-33 years) performed standing computerized dynamic posturography balance tasks across progressively increasing amplitudes of visual (VIS), somatosensory (SOM) and both (VIS+SOM) systems perturbation conditions. Adaptation in the motor strategy was measured as changes in electromyographic (EMG) activities and joint angles. The contribution of the perturbed sensory input in maintaining postural stability was calculated to determine the sensory reweighting. A multivariate design was used to model a linear combination of motor adaptation variables that discriminates specific sensory integration tasks. Results showed a significant progressive decrease in postural sway per unit amplitude of sensory perturbation in each condition, indicating dynamic sensory reweighting. Linear discriminant function analysis indicated that the adaptation in motor strategy during the VIS condition was associated with increased activity of EMG and joint angles in the upper body compared to the lower body. Conversely, during the SOM and VIS+SOM conditions, the adaptation in motor strategy was associated with decreased activity of EMG and joint angles in the lower body compared to the upper body. Therefore, the adaptation in motor strategies associated with sensory reweighting were different for different sensory integration tasks.