The cognitive behavioural profile of individuals with autistic spectrum disorder (ASD) includes difficulties with sustained attention, temporal foresight, forward planning and decision-making. However, little is known of the neurofunctional substrates underlying these deficits, nor how functional brain maturation during these crucial cognitive functions may differ in people with ASD.
We used fMRI across 90 children and adults (11-35 years old) with ASD and typically developing controls to investigate 1) differences in brain activation in children and adults with ASD relative to controls during three tasks that measure sustained attention, temporal discounting and decision-making and 2) differences in neurofunctional maturation in people with ASD relative to controls.
46 males (11-35 years old) with ASD and 44 age/IQ matched typically developing male controls completed three event-related fMRI tasks on a 3T MRI scanner. All participants were right-handed, medication-naïve, IQ >70. All individuals with ASD were diagnosed with autism or Asperger (ICD-10) and met ADI and ADOS cut-offs for autism. The 12 minute parametric sustained attention task (SAT) requires subjects to respond as quickly as possible to a timer that appears under two delay conditions: 1) short, frequent, predictable delays (500ms), 2) randomly interspersed long, unpredictable delays (2s, 5s, 8s). Long unpredictable delays place a higher load on sustained attention (parametrically modulated with increasing delays); short predictable delays place a higher load on sensorimotor timing. The 12 minute temporal discounting task (TD) measures the effect of delay on reward-related decision making and temporal foresight. Subjects choose between small immediate rewards and larger delayed rewards. The 20 minute Gambling Task (GT) measures temporal bridging during long-term decision making, reward anticipation and the effects of monetary gain/loss on brain activation. Subjects choose between cards that result in high immediate gain, but larger future loss (“risky”: long-term loss), or lower immediate gain, with a large final reward (“safe”: long-term gain). Data were analysed using non-parametric image analysis (XBAM: www.brainmap.co.uk). To investigate whether group differences in brain activation were associated with differential neurofunctional development, we performed conjunction analyses between group differences in activation and group differences in whole-brain age correlations.
SAT: Individuals with ASD had slower reaction times and greater intrasubject variability than controls and underactivated dorsolateral and inferior prefrontal, striato-thalamic, temporal and cerebellar regions. The conjunction analysis showed that most of these regions that differed significantly between groups also differed in functional maturation; they increased progressively with age in controls, but not in ASD. Furthermore, abnormal activation and functional maturation in frontal regions was associated with poorer task performance and clinical measures of ASD and attention.
TD and GT: data will be presented at the conference.
Findings suggest that individuals with ASD have significant differences from controls in the functional activation of brain networks central to sustained attention, temporal discounting and decision-making. Importantly, this study shows that functional activation deficits across 3 tasks in ASD are associated with underlying abnormalities in functional brain maturation, suggesting that abnormal brain function may be due to abnormal functional maturation.
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