ADHD and ASD: distinct brain patterns of inhibition-related activation?

Abstract

Attention-deficit/hyperactivity (ADHD) and autism spectrum (ASD) disorders often co-occur. In both cases, response inhibition deficits and inhibition-related atypical brain activation have been reported, although less consistently in ASD. Research exploring the overlap/distinctiveness between ADHD and ASD has significantly increased in recent years, but direct comparison of the inhibition-related neuronal correlates between these disorders are scarce in the literature. This study aimed at disentangling the shared and specific inhibitory brain dysfunctions in ASD and ADHD. Using functional magnetic resonance imaging (fMRI), brain activity was compared between children with ADHD, ASD and typically developing (TD) children aged 8-12 years during an inhibition stop-signal task, using stringent inclusion criteria. At the behavioural level, only children with ADHD exhibited inhibition deficits when compared with the TD group. Distinct patterns of brain activity were observed during successful inhibition. In children with ADHD, motor inhibition was associated with right inferior parietal activation, whereas right frontal regions were activated in children with ASD. Between-group comparisons disclosed higher middle frontal activation in the ASD group compared with the ADHD and the TD groups. Our results evidence different patterns of activation during inhibition in these two disorders, recruiting different regions of the fronto-parietal network associated to inhibition. Besides brain activity differences, behavioural inhibition deficits found only in children with ADHD further suggest that reactive inhibition is one of the core deficits in ADHD, but not in ASD. Our findings provide further evidence contributing to disentangle the shared and specific inhibitory dysfunctions in ASD and ADHD.

Fig. 1. Schematic illustration of the stop-signal task.

a Participants are instructed to respond as accurately and quickly as possible to go signals, i.e., arrows pointing to the left (n = 100) or to the right (n = 100), with a left or right button press according to the direction of the arrow. Display duration depended on participant’s response speed, lasting a maximum of 500 ms. In 25% of the trials, pseudo-randomly interspersed, a stop stimulus (arrow pointing upwards) was presented shortly after the go signal (20 after a right-oriented go stimulus, 20 after a left-oriented go stimulus) and participants were instructed to answer as fast and accurately as possible to the go signal, and to attempt cancelling their ongoing motor response (i.e., not responding) when the stop signal appeared. They were also encouraged not to wait for the stop signal to appear before responding. All trials included a 1000 ms fixed response interval, followed by a variable interval randomly set between 600 ms and 900 ms. b Initially, the stop stimulus was displayed 250 ms (Stop Signal Delay, SSD) after the go signal. A tracking algorithm adjusted subsequent SSDs trial-by-trial by steps of 50 ms according to the participant’s performance. If inhibition was successful, then the SSD was made longer by 50 ms to make inhibition of the ongoing response more difficult. If inhibition failed, then the SSD was made shorter by 50 ms to facilitate inhibition. The task involved a total of 200 trials (160 go and 40 stop), requiring a total scan time of ~8 min.

Fig. 2. Brain activation during Successful Stop versus Go at the cluster level p^FWE < 0.05.

a Within-group activation in a cluster comprising the right angular gyrus/intraparietal sulcus and inferior parietal gyrus in the ADHD group (x = 36, y = −56, z = 34; p < 0.001) and in the right middle frontal gyrus in the ASD group (x = 42, y = 18, z = 46; p < 0.001). b Between-group comparison showing higher activation in the right cingulate gyrus/middle frontal gyrus and the left middle frontal gyrus in children with ASD compared with the ADHD group and in the right middle frontal gyrus in children with ASD compared with the TD group.

Fig. 3

Percent signal change in activation during successful stop and go in regions showing between-group significant differences: a the right cingulate gyrus/ right middle frontal gyrus (x = 16, y = 24, z = 42), b the left middle frontal gyrus (x = −22, y = 16, z = 42) and c the right middle frontal gyrus (x = 40, y = 20, z = 44).