Cross Sectional Associations Between Measures of Social Function, Postural Control and Motor Coordination

Background:  Autism Spectrum Disorders (ASD) are c disorders of social communication and behaviour. Research and treatment focus is on the cognitive, social and behavioural aspects of ASD. Yet motor skill and postural control are significantly different in people with ASD with effect strength of 1.2. Postural control is needed for both social function and motor skill. The pattern of movement of the centre of pressure (COP) during standing represents the control processes underlying postural control. Sample entropy measures the regularity or amount of information in a signal. Less entropy in the COP signal indicates more regular COP fluctuations and more active control of posture. The effective use of visual information is critical to the development of motor function, postural control and social function. The relationship between social function, postural control and motor coordination has not been reported in research literature. The relationship among these factors may inform potential causal pathways in ASD.

Objectives:

To determine the cross sectional associations between measures of social function, postural control and motor coordination.

Methods:

Cross sectional study design. 49 adults selected for their ASD status (n=19) or typically developed (TD) status (n=29) were tested for postural control in quiet stance during eyes open (EO) (30 seconds) and eyes closed (EC) (30 seconds). Only 46 had complete data for postural control (3 TD missing). The sample entropy of each 30 second signal was calculated for the mediolateral (ML) and anterior-posterior (AP) sway. Motor coordination was assessed using the McCarron Assessment of Neuromuscular Development (MAND)-the MAND gross motor (GM) score was used. ASD symptomology was assessed using the Social Responsiveness Scale (SRS-2). All measures were continuous and were compared using Pearson correlation with p<0.05 considered as statistically significant. Stepwise linear regression with pin=0.05 and pout=0.10 was undertaken.

Results:

Correlations were statistically significant between the SRS-2 score and the MAND GM score (r=-0.445, p=0.002); the MAND GM score and the sample entropy of the mediolateral sway component during eyes open (r=-0.355, p=0.015). Entropy measures with eyes closed (EC-AP, EC-ML) were not significantly related to the MAND GM score or the SRS-2 (p>0.508). EO-AP sample entropy was not significantly related to the SRS-2 score at p=0.082 (r=-0.259). Stepwise linear regression of SRS-2 against the other variables resulted in a model that explained 23% of the variance (adjusted r square) in the SRS-2 score. SRS-2 = 81.735-0.381 (SE 0.112)(MAND GM) -61.298 (SE 26.992)(sample entropy EO-AP).

Conclusions: Nearly one quarter of variation in social impairment (higher SRS-2) could be explained by poorer gross motor function (lower MAND GM) and more active control of sway in the AP direction with vision. AP sway is generally controlled by the somatosensory system. The findings suggest that these factors are independently related to social impairment. Poor gross motor function was related to a less controlled posture in the mediolateral direction. Mediolateral sway is controlled primarily by visual fixation and the finding supports the hypothesis that poor gross motor function may be related to a lower sensory weighting of vision in postural control.