Individuals with cerebral palsy show altered responses to visual perturbations during walking

Abstract

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.

Immediate application of low-intensity electrical noise reduced responses to visual perturbations during walking in individuals with cerebral palsy

“…The demographic characteristics of both groups are reported in our previously published work (11). The descriptive statistics for all outcome measures are presented in Supplementary Table 1.…”

“…Further, worsening of crouch stance was observed after removing visual input, thus indicating the dominant role visual input plays in control of standing balance in individuals with CP. With respect to walking, our recent work investigated how individuals with CP use visual input for walking balance control compared to their age-and sexmatched peers by subjecting them to visual sideways fall stimuli while walking in a virtual environment (11). Our results showed that individuals with CP had a magni ed and delayed response to visual perturbations, thus implying that they were more affected by changes in visual input and hence, relied more on vision for walking balance control.…”

“…We then calculated the average foot placement response over the rst three post-perturbation steps as a measure of the overall foot placement response following a visual perturbation. These outcome measures have been previously used to assess the response to visual perturbations in individuals with CP (11) and in neurotypical healthy adults (24,28).…”

“…The scene remained tilted for 2000 ms and then reset to the horizontal over the next 1000 ms with a constant angular velocity. These perturbations mimic the optic ow of falling sideways around the stance foot and have been used extensively in our previous work (11,24,26,28). The perturbations were triggered at pseudo-randomly selected heel strikes of either foot, where each such trigger was followed by a 10-12 step washout period between the reset of the visual scene and the next trigger.…”

“…The two biomechanical mechanisms typically used to modulate lateral CoM movement during walking are: (a) ankle roll, which involves using lateral ankle musculature to bring about inversion at the stance ankle and pull the body to one side, (25,26), and (b) the foot placement, which involves stepping in the direction of a perceived fall to help accelerate the movement of the body away from the fall in subsequent steps (24,27). Prior work (11) showed that compared to typically developing peers, individuals with CP respond to visual perturbations with reduced ankle roll and increased foot placement change. In this study, we seek to investigate how these underlying biomechanical mechanisms are affected by augmented proprioceptive input through SR. Our hypothesis is that with SR, individuals with CP will show a reduction in ankle roll and foot placement response, which would in turn be the mechanism for the hypothesized decrease in overall CoM response.…”