Inhibitory Control Deficits in ASD Reflect Failures to Strategically Delay Behavioral Responses

Background:  Deficits of behavioral response inhibition, including reduced abilities to suppress contextually inappropriate behaviors, have been repeatedly documented in ASD. We recently demonstrated that healthy individuals are more likely to inhibit unwanted behavioral responses when they strategically delay their onset. Determining the extent to which individuals with ASD use similar cognitive strategies to support response inhibition across childhood and into adulthood may provide important insights into cognitive processes underlying reduced inhibitory control in ASD.

Objectives:  To characterize behavioral response inhibition and underlying neurocognitive strategies in children, adolescents, and adults with ASD using a stop-signal task (SST).

Methods: One hundred twenty-two individuals with ASD and 76 healthy controls matched on age (5-28 years), gender, and nonverbal IQ completed a manual motor SST. Participants were instructed to press a button when a peripheral target appeared ('GO' trials) or inhibit these responses when a central stop-signal appeared following the peripheral cue (‘STOP’ trials). A baseline reaction time (RT) task consisting of a block of GO trials was administered to assess adaptive RT slowing during SST GO trials. Non-linear regression models were used to assess the relationship between SST accuracy and slowing as function of age. The Repetitive Behavior Scale-Revised (RBS-R) was used to assess the relationship between SST performance and repetitive behaviors in patients.

Results:  Individuals with ASD showed reduced rates of successfully inhibiting motor responses on STOP trials compared to controls. Participants slowed their RTs during SST GO trials compared to baseline, but individuals with ASD slowed their RTs less than controls. Greater RT slowing was associated with reduced inhibition error rates for participants, and this relationship was stronger for controls than patients. Participants demonstrated age-related increases in stopping accuracy and RT slowing that were best modeled as a cubic function. Individuals with ASD showed less age-related increases in SST accuracy and slowing. Reduced stopping accuracy and RT slowing were associated with more severe repetitive behaviors, including compulsive, self-injurious, and ritualistic behaviors.

Conclusions: Our results provide novel evidence that deficits inhibiting behavioral responses in ASD may reflect a reduced ability to strategically delay the onset of motor responses. Whereas healthy individuals slow their behavioral responses in uncertain conditions and thereby increase their ability to suppress inappropriate responses, individuals with ASD are less able to use this strategy and therefore have greater difficulty suppressing unwanted responses when they are cued to stop. Our findings that deficits of inhibitory control are related to repetitive behaviors suggest that patients’ failures to suppress attention to or engagement in a particular behavior may contribute to their compulsive and ritualistic actions. Our findings also suggest that treatments aimed at slowing behavioral responses may mitigate impulsive behavioral responses and repetitive behaviors in ASD, and that these treatments may continue to be effective if implemented in later childhood or adolescence.