Behavioral Response Inhibition Deficits in Individuals with Autism Spectrum Disorder and Their Parents

Background: Individuals with autism spectrum disorder (ASD) show deficits in behavioral response inhibition, or the ability to suppress contextually inappropriate behaviors. We previously reported that response inhibition also is impaired in unaffected parents and siblings of children with ASD, suggesting that this deficit may be familial and serve as a useful intermediate phenotype for determining pathophysiological processes.

Objectives: To examine if deficits in response inhibition are evident in both individuals with ASD and their biological mothers and fathers.

Methods: Four participant groups completed a manual motor Stop Signal task (SST). Fifty-three probands with ASD ages 5-23 years were matched with 25 typically developing controls (ConPro) on age (5-23 years), gender, and nonverbal IQ. One hundred parents of the ASD (ASD parents) sample ages 29-54 years were matched with 43 typically developing adults (ConPts) on age (28-51 years), gender, and nonverbal IQ. For the SST, participants were seated with their thumbs resting on a button-box. Two types of trials were presented. During “GO” trials, a peripheral “GO” target appeared and participants were instructed to press the button corresponding to the side of the screen where the target appeared. During “STOP” trials, a central cue appeared at a variable delay after the “GO” cue indicating that they should inhibit their response. Prior to the SST, participants completed a block of GO trials to determine their baseline reaction times. We also examined participants’ reaction times for SST GO trials and their rate of successfully inhibiting responses on STOP trials.

Results: Individuals with ASD showed increased rates of stopping errors compared to ConPro (t(76)=-2.225, p=0.029). Participants increased their reaction times from baseline to SST GO trials, (t(206)=34.400, p<0.001). Individuals with ASD showed a smaller increase in reaction time from baseline to SST GO trials compared to controls (t(62)=-2.108, p=0.039). Greater increases in reaction time from baseline to SST GO trials were associated with increased rates of inhibition on STOP trials for probands (r(39)=.459, p=0.003) and ConPro individuals (r(21)=.753, p<0.001). This relationship was marginally stronger in ConPro than ASD individuals (z=1.75, p=0.080). ASD parents also showed increased rates of stopping errors compared to ConPts (t(141)=-2.333, p=.021). ASD parents showed lower reaction times at baseline (t(141)=-2.766, p=0.006) and during SST GO trials compared to ConPts (t(141)=-2.786, p=0.006). However, these groups did not differ on the degree to which they slowed their reaction times from baseline to SST GO trials (p>.05). Reduced rates of inhibiting STOP trials were associated with smaller increases in reaction time from baseline to SST GO trials for the ASD parents (r(98)=.488, p<0.001) and the ConPts (r(41)=.305, p=.047).

Conclusions: Our findings show that individuals with ASD have a reduced ability to inhibit inappropriate behaviors, and that these deficits reflect a failure to strategically delay the onset of these behaviors. Similar patterns of increased rates of stopping errors and reduced behavioral reaction times were seen in unaffected parents of individuals with ASD, suggesting that deficits in inhibitory control processes may be familial in ASD and useful for identifying pathogenic mechanisms.