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January

Differences in brain dysfunctions in children with Attention Deficit Hyperactivity Disorder and in children with Conduct Disorder

13 January 2009

Professor Katya Rubia of the Institute of Psychiatry and colleagues have recently published a study in the American Journal of Psychology showing that the underlying neurobiological substrates of Attention Deficit Hyperactivity Disorder (ADHD) and those with Conduct Disorder (CD) appear to be very different.

Children with ADHD and those with Conduct Disorder CD overlap behaviourally in their symptoms and in their cognitive profile and are therefore often difficult to differentiate clinically

Prof Katya Rubia and colleagues used magnetic resonance imaging (fMR)I to compare the underlying neurophysiological substrates during the performance of a rewarded sustained attention task -measuring sustained attention and motivation- in medication-naïve boys with pure ADHD and in those with pure CD as well as healthy children.

The findings showed no differences between patients in task performance, but clear differences in the brain dysfunctions during task performance compared to controls. There was a process-related dissociation of prefrontal lobe dysfunction in both disorders. Children with ADHD showed disorder-specific reduction in inferior prefrontal activation during the 'cool' cognitive aspect of the task, during sustaining attention, while children with CD showed a disorder-specific dysfunction in the orbitofrontal cortex during the 'hot', motivational aspect of the task, i.e. during the reward effect. Furthermore, CD children showed reduced activation in limbic and paralimbic regions -thought to be important for motivation- during the 'cool' cognitive aspects of the task (sustained attention). The findings show that despite showing similar (poor) cognitive performance, children with ADHD and with CD are doing so with different underlying pathophysiology: ADHD children show disorder-specific abnormalities in inferior prefrontal cortex mediating attention processes, while children with CD show abnormalities in the paralimbic system of the brain, comprising orbitofrontal cortex and limbic regions, that mediates motivation.

The findings provide neurobiological evidence for the theory that CD is more related to abnormalities of paralimbic motivation networks, while ADHD is related to a dysfunction in lateral fronto-striatal attention networks. This study is a first step towards the delineation of the specific biomarkers of the two diagnostic disorders which aims to contribute to the development of a more objective phenomenological differentiation and the development of disorder-specific tailored treatment.

Copy of the Full Paper: http://ajp.psychiatryonline.org/cgi/reprint/166/1/83

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