Sensory Feedback Mechanisms Underlying Postural Control Abnormalities in Individuals with Autism Spectrum Disorder (ASD): A Preliminary Study

Background: Postural control abnormalities have been demonstrated in some but not all studies of autism spectrum disorder (ASD). These prior studies have quantified the amount of sway during standing, but stability also depends on each individual’s postural limitation boundary, or the maximum extent to which they may sway in each direction without losing their balance. In the present study, we examined postural sway relative to each individual’s postural limitation boundary (virtual time to contact; VTC) in individuals with ASD and healthy controls (Fig.1A). 

Objectives: To examine the range of center of pressure (COP) fluctuations as well as spatial and temporal VTC complexity for individuals with ASD and healthy controls during both static and dynamic standing postures. 

Methods: Six children with ASD (ages 11-16 yrs) and 6 healthy controls matched on age, sex and non-verbal IQ completed tests of static and dynamic stances. Prior to testing, participants were instructed to stand side-by-side with their feet shoulder width apart on a force platform. Their foot position was traced on the platform so that their starting position at the beginning of each trial was consistent. Participants’ postural limitation boundary was determined by having them leaning their body in each of four different directions (anterior, posterior, left and right) as far as they could without fallingand then fitting an ellipse to the COP maxima for each direction (Fig. 1B). COP measurements were derived from the force platform output.

During static stance trials, participants were instructed to stand as still as possible. During dynamic stance trials, participants were instructed to continuously sway their body either anterior-posteriorly (AP) or medial-laterally (ML) at a comfortable speed. Participants completed three 30-sec trials for each stance. Each participant’s VTC was derived by comparing the spatial and temporal relation between their postural limitation boundary and their COP collected during each trial. To examine participants’ ability to dynamically adjust their postural sway over time in response to sensory feedback, the spatial and temporal complexity of each participant’s VTC also were compared. 

Results: During static stance, individuals with ASD showed increased COP range of motion in both AP and ML directions (p <0.05) and decreased spatial and temporal VTC complexity (p<0.05). During dynamic stances, patients showed reduced COP range of motion in each postural sway condition (p<0.05), but again they showed decreased VTC complexity in both spatial and temporal domains (p<0.05). 

Conclusions: Our findings suggest that individuals with ASD show reduced postural stability relative to controls, but the quality of this deficit varies across different types of postural conditions. While traditional measures of postural stability highlight both increases and decreases in sway during static and dynamic stances, respectively, we find that the spatial and temporal complexity of patients’ sway is reduced in ASD across stances. Thus, patients demonstrate deficits in their ability to dynamically adjust their balance across different postural conditions reflecting a reduced ability to integrate sensory feedback to maintain postural stability.