Postural orientation and equilibrium processes associated with increased postural sway in autism spectrum disorder (ASD)

Abstract

BackgroundIncreased postural sway has been repeatedly documented in children with autism spectrum disorder (ASD). Characterizing the control processes underlying this deficit, including postural orientation and equilibrium, may provide key insights into neurophysiological mechanisms associated with ASD. Postural orientation refers to children’s ability to actively align their trunk and head with respect to their base of support, while postural equilibrium is an active process whereby children coordinate ankle dorsi-/plantar-flexion and hip abduction/adduction movements to stabilize their upper body. Dynamic engagement of each of these control processes is important for maintaining postural stability, though neither postural orientation nor equilibrium has been studied in ASD.MethodsTwenty-two children with ASD and 21 age and performance IQ-matched typically developing (TD) controls completed three standing tests. During static stance, participants were instructed to stand as still as possible. During dynamic stances, participants swayed at a comfortable speed and magnitude in either anterior-posterior (AP) or mediolateral (ML) directions. The center of pressure (COP) standard deviation and trajectory length were examined to determine if children with ASD showed increased postural sway. Postural orientation was assessed using a novel virtual time-to-contact (VTC) approach that characterized spatiotemporal dimensions of children’s postural sway (i.e., body alignment) relative to their postural limitation boundary, defined as the maximum extent to which each child could sway in each direction. Postural equilibrium was quantified by evaluating the amount of shared or mutual information of COP time series measured along the AP and ML directions.ResultsConsistent with prior studies, children with ASD showed increased postural sway during both static and dynamic stances relative to TD children. In regard to postural orientation processes, children with ASD demonstrated reduced spatial perception of their postural limitation boundary towards target directions and reduced time to correct this error during dynamic postural sways but not during static stance. Regarding postural equilibrium, they showed a compromised ability to decouple ankle dorsi-/plantar-flexion and hip abduction/adduction processes during dynamic stances.ConclusionsThese results suggest that deficits in both postural orientation and equilibrium processes contribute to reduced postural stability in ASD. Specifically, increased postural sway in ASD appears to reflect patients’ impaired perception of their body movement relative to their own postural limitation boundary as well as a reduced ability to decouple distinct ankle and hip movements to align their body during standing. Our findings that deficits in postural orientation and equilibrium are more pronounced during dynamic compared to static stances suggests that the increased demands of everyday activities in which children must dynamically shift their COP involve more severe postural control deficit...

Postural control processes during standing and step initiation in autism spectrum disorder

“…Studies of postural control in ASD have implicated sensory feedback processes. Individuals with ASD are less stable than typically developing (TD) controls during standing [1,2,[16][17][18], and they show more severe postural control deficits, including increased postural sway, when sensory feedback information is occluded or removed [1,3,17,19]. These findings suggest that individuals with ASD may place greater demands than controls on feedback processes in order to maintain stability.…”

“…Individuals with ASD also show more severe postural control deficits during dynamic postures. For example, Wang et al (2016) found that individuals with ASD demonstrated increased center of pressure (COP) variability during a dynamic stance condition in which they intentionally swayed along the mediolateral (ML) or anteroposterior (AP) axis. Elevations in COP variability in ASD were more severe during the dynamic compared to a static standing condition, suggesting that individuals with ASD show greater levels of impairment during conditions in which demands on feedback motor control processes are increased [18].…”

“…For example, Wang et al (2016) found that individuals with ASD demonstrated increased center of pressure (COP) variability during a dynamic stance condition in which they intentionally swayed along the mediolateral (ML) or anteroposterior (AP) axis. Elevations in COP variability in ASD were more severe during the dynamic compared to a static standing condition, suggesting that individuals with ASD show greater levels of impairment during conditions in which demands on feedback motor control processes are increased [18]. While few studies have examined postural control during dynamic conditions, control during dynamic postural adjustments more closely relates to activities of daily living than static stances and therefore may be informative for determining more clinically relevant postural issues.…”

“…Coordination of joint movements is necessary to maintain postural stability. When standing still, processes that control ML sway, including abduction and adduction of hip joints, and AP sway, including dorsi and plantar flexion of ankle joints, are coordinated to simultaneously correct sway in multiple directions [18,20,21]. During static stance in healthy individuals, these distinct processes show moderate cross-talk, or mutual information (MI), which helps modulate sway in all directions.…”

Dissociating proprioceptive deficits in Autism Spectrum Disorders: Intact acuity but impaired sensory integration in postural control

“…The ankle angle for the 8-minute trial was segmented into sixteen 30s time windows and Standard Deviation (SD) was calculated in each window. SD has been previously used in studies assessing postural control in ASD (Wang et al, 2016). Spectral properties of the ankle angle waveforms in the first (a1) and last (a6) windows of adaptation were also calculated.…”