Researchers scanned the brains of 60 boys aged 11 to 17 while they did a task that asked them to stay focused over time. None had taken medication before. Twenty had combined-type ADHD, twenty had autism, and twenty were healthy boys matched for age and IQ. All had an IQ of at least 70, and all were right-handed.
The two conditions shared some patterns. Compared with the healthy boys, both the ADHD and the autism groups showed less activity in several brain areas linked to attention and control. Both groups also failed to quiet down a network that normally switches off during focused work.
There were also differences tied to each condition. Boys with ADHD showed a stronger drop in activity in one front-of-brain region than boys with autism (P 0.001 versus controls). Boys with autism showed extra activity in the cerebellum, higher than in both other groups (P 0.0001 versus controls). The ADHD boys were also the least steady in their response times (group difference P=0.003).
The study was small, with only 20 boys per group and no girls. Twelve of the autism group scored high on attention problems. The authors did not test their idea about the extra cerebellum activity.
Source: Anastasia Christakou, Clodagh M. Murphy, Kaylita Chantiluke, et al.. Disorder-specific functional abnormalities during sustained attention in youth with Attention Deficit Hyperactivity Disorder (ADHD) and with Autism. Molecular Psychiatry (2012). doi:10.1038/mp.2011.185
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