Individuals with cerebral palsy (CP) have deficits in processing of somatosensory and proprioceptive information. To compensate for these deficits, they tend to rely on vision over proprioception in single plane upper and lower limb movements and in standing. It is not known whether this also applies to walking, an activity where the threat to balance is higher. Through this study, we used visual perturbations to understand how individuals with and without CP integrate visual input for walking balance control. Additionally, we probed the balance mechanisms driving the responses to the visual perturbations. More specifically, we investigated differences in the use of ankle roll response i.e., the use of ankle inversion, and the foot placement response, i.e., stepping in the direction of perceived fall. Thirty-four participants (17 CP, 17 age-and sex-matched typically developing controls or TD) were recruited. Participants walked on a self-paced treadmill in a virtual reality environment. Intermittently, the virtual scene was rotated in the frontal plane to induce the sensation of a sideways fall. Our results showed that compared to their TD peers, the overall body sway in response to the visual perturbations was magnified and delayed in CP group, implying that they were more affected by changes in visual cues and relied more so on visual information for walking balance control. Also, the CP group showed a lack of ankle response, through a significantly reduced ankle inversion on the affected side compared to the TD group. The CP group showed a higher foot placement response compared to the TD group immediately following the visual perturbations. Thus, individuals with CP showed a dominant proximal foot placement strategy and diminished ankle roll response, suggestive of a reliance on proximal over distal control of walking balance in individuals with CP.

Introduction: Individuals with cerebral palsy (CP) compensate for deficits in somatosensory processing by relying on visual input over proprioception for balance control. Upweighting, i.e., increasing reliance on proprioception, helps free up vision for high-level use like navigation and obstacle avoidance. We hypothesize that children with CP will be able to upweight proprioception and reduce visual reliance if their proprioception is improved. A promising technique to improve proprioception is the use of Stochastic Resonance (SR) stimulation, which uses random, sub-sensory, electrical current to improve proprioception. The aim of this study is to investigate if SR stimulation results in reduced reliance on vision during visually perturbed walking in individuals with and without CP. We hypothesized that the responses to visual perturbations would be smaller with SR stimulation vs. without SR. We also investigated how the two balance mechanisms driving the responses to the visual perturbations, ankle roll and foot placement, were affected by SR stimulation. Methods: Seventeen ambulatory individuals (age 16.3 ± 4.3, 8 males) with spastic diplegic or hemiplegic CP and seventeen age-and sex-matched individuals with typical development (TD, age 16.1 ± 4.2) were recruited. SR stimulation was applied to the muscles and ligaments of ankle and hip joints. Participants walked on a self-paced treadmill in a virtual reality environment that induced a visual perturbation in the frontal plane once every 10-12 steps. Participants completed three trials of two minutes each of SR stimulation (SR) and no stimulation (noSR) in randomized order. We performed two-way mixed ANOVAs, with group (CP, TD) as between-subject and condition (noSR, SR) as within-subject factors. Results:The response to visual perturbations was significantly smaller with SR in the CP group (p<0.001), but not in the TD group (p=0.883). There was no significant effect of stimulation on the use of ankle roll and foot placement in either group. Conclusion:The reduced response to visual perturbations in the CP group supports our hypothesis that SR stimulation allows children with CP to upweight proprioception and reduce visual reliance. However, the balance mechanisms that are driving these changes in the response to visual perturbation are unclear.