Researchers pooled brain-scan studies to see how people with ADHD used their brains during two kinds of tasks: holding back a response (inhibition) and paying attention. They combined 21 data sets for inhibition (287 people with ADHD and 320 without) and 13 data sets for attention (171 with ADHD and 178 without). The samples included both children and adults. Patients who were taking medication stopped it for at least 18 hours before the scan.
During inhibition tasks, people with ADHD showed less activity than controls in several right-side and deep-brain regions, including the right inferior frontal cortex and an area tied to planning movement.
During attention tasks, they showed less activity in a different set of right-side regions, and more activity in the right cerebellum and part of the left rear of the brain.
The two patterns barely overlapped, which suggested that inhibition and attention rely on separate networks.
The study also looked at medication. The more patients had taken long-term stimulants, the more activity appeared in one deep-brain region (r = 0.233). Patients who had never taken medication had less activity than controls. The authors called this a preliminary result, based on only 37 medicated patients (21.6% of 171).
Source: Hart H, Radua J, Nakao T, et al.. Meta-analysis of Functional Magnetic Resonance Imaging Studies of Inhibition and Attention in Attention-deficit/Hyperactivity Disorder. JAMA Psychiatry (2013). doi:10.1001/jamapsychiatry.2013.277
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