To investigate brain function in children and adolescents with ASD and healthy Controls during a task that measures sustained attention and sensorimotor timing.
28 children and adolescents (11-18 years old) with ASD and 16 age and IQ matched child and adolescent controls completed an event-related parametric Psychomotor Vigilance Task with different temporal delay conditions on a 3T magnetic resonance imaging (MRI) scanner. All participants were male, right-handed, with an IQ >70. All individuals with ASD met algorithm cut-offs for autism on both the ADI & ADOS. The task requires a motor response to a visual stimulus that appears under qualitatively and quantitatively different delay conditions: 1) long, unpredictable delays of 2s, 5s and 8s and 2) one short predictable delay period of 500ms. Long unpredictable delays have a higher load on sustained attention, while short predictable delays in the milliseconds range are known to trigger sensorimotor synchronisation. Data were analysed using non-parametric image analysis (XBAM).
Children and adolescents with ASD compared to healthy controls were slower in their reaction times to the 3 unpredictable long delays, but showed no differences in their reaction times to the short delay of 500ms. The fMRI contrasts between all three unpredictable long delays (2s,5s,8s) compared to the predictable short delay showed reduced brain activation in children and adolescents with ASD compared to healthy controls in a right hemispheric sustained attention network of ventrolateral prefrontal cortex, superior temporal lobe, putamen, thalamus and anterior and posterior cingulate. Furthermore, brain dysfunctions became progressively more extensive and bilateral with increasing temporal delay (from 2s to 8s). For the contrast of the short, sensorimotor condition, with long delays, children and adolescents with ASD showed reduced activation in the cerebellum, known to be important for motor timing, and in posterior cingulate and precuneus, presumably related to visual-spatial attention.
Results suggest that children and adolescents with ASD have extensive abnormalities in fronto-striato-thalamo-temporal networks of sustained attention that increase with increasing attention load, as well as in cerebello-cingulate posterior regions for sensorimotor timing. It is possible that the extensive brain differences observed during sustained attention to temporally unpredictable events relate to the need for 'sameness' displayed by some individuals with ASD.