Relationship Between Postural Control and Restricted, Repetitive Behaviors in Autism Spectrum Disorders

Background: Restricted interests and repetitive stereotyped behaviors (RRBs) are one of the core diagnostic areas of autism spectrum disorders (ASD).  Poor motor control has been reported to be predictor of repetitive behavior in individuals with mental retardation; however the relationship between motor control and repetitive behaviors in ASD is not fully defined.
Objectives: We compared the center of pressure (COP) sway area during quiet stance with intensity and frequency scores on the Repetitive Behavior Scale-Revised (RBS-R) in children with ASD and typically developing controls (TD).  Our goals were to determine whether subjects with ASD had greater postural sway and whether RBS-R scores were related to the magnitude of postural sway.  Further, we want to examine profiles of abilities in the group with ASD.
Methods: We have currently enrolled 18 children (IQ>70) diagnosed with ASD (3.9 to 15.7 yrs) and 28 TD children (3.4 to 15.9 yrs). Parents completed the RBS-R to determine the frequency and intensity of RRBs: Stereotyped Behavior, Self-Injurious Behavior, Compulsive Behavior, Ritualistic Behavior, Sameness Behavior and Restricted Behavior.  Subjects also performed four quiet stance trials at a self–selected stance width for 15 seconds. Foot positioning was marked on the initial trial and used for all subsequent trials.  Ground reaction forces were recorded (360Hz) from a forceplate (Type 4060–10, Bertec Corp., Columbus, OH) embedded level within the floor to calculate COP.
Results: Subjects with ASD had greater postural sway area compared to controls (p=0.003). Not surprisingly, subjects with ASD exhibited greater frequencies and intensities of RRBs overall and on all 6 subscales.  Visual analysis of the postural sway area for the ASD group suggests that roughly half scored comparable to TD controls, whereas the other half scored >2 SD outside the TD range.  Preliminary analyses found that motor impaired children did not have significantly worse IQ scores, but were younger (p=0.02) and had greater frequencies and intensities on the Stereotypies, Compulsive, and Restricted subscales (p<0.05).
Overall postural sway area was significantly correlated with the Total RBS-R frequency and intensity scores (r=.52, p<0.001 and r=.54, p<0.001), as well as 5 subscale scores (r range of .37 to .65, all p<0.01). Sway area was not related to the Self-injurious Behavior subscale.  When examining the groups separately, however, these relationships appear to be driven by the strong correlations within the group with ASD; whereas, in controls postural sway was only related to the frequency and intensity of self injurious behavior.
Conclusions: Results support previous findings of relationships between RRBs and postural control. Motor control deficits in ASD continue to be more well-defined.  It appears that motor control impairments may characterize a subset of individuals with ASD.  Better delineation of function in these individuals will be important.  Findings from animal and human neurobiological studies suggest that cortico-striato-thalamo-cortical circuits are involved in RRBs and motor and cognitive functions.  These findings support a model relating RRBs in autism to deficits in motor control and cognitive functions (e.g. cognitive flexibility).  We are continuing to collect data to examine these relationships.