Scientists pinpoint unique brain abnormalities in children with ADHD
09 July 2010
Two separate studies from Professor Katya Rubia and colleagues at the Institute of Psychiatry (IoP), King’s College London (KCL), show that children with Attention Deficit Hyperactivity Disorder (ADHD) have unique brain abnormalities in parts of the brain responsible for inhibiting behaviour, switching between tasks and attention processing compared to other childhood disorders such as conduct disorder (CD) and obsessive-compulsive disorder (OCD).
The findings show that childhood disorders can be characterised by unique brain function abnormalities. Disentangling the specificity of the underlying brain abnormalities of psychiatric disorders will ultimately help towards establishing disorder-specific biomarkers that can aid to a more objective diagnosis and help with the development of disorder-tailored treatment.
The first study compared children with ADHD and those with CD while the second compared children with ADHD and OCD. Children with ADHD and those with CD overlap behaviourally in their symptoms and in their cognitive profile and are therefore often difficult to differentiate clinically. However, these new studies show that they may have different underlying brain deficits.
In the studies, scientists looked into how different areas of the brain would engage in various cognitive tasks, amongst children with different disorders using functional magnetic resonance imaging (fMRI). Their findings show differences in brain activation, depending on the cognitive task and condition.
The first fMRI study to appear soon in Human Brain Mapping compared children with ADHD and with CD in their brain activation while they performed tasks where they had to inhibit their behaviour and switch between different tasks, which are difficult for both disorders. The findings showed differences in the brain deficits during performance. A section of the brain, which is crucial for these abilities, was reduced in activation in children with ADHD compared to both healthy children and children with CD. The findings extend a series of studies from this group showing disorder-specific abnormalities in ADHD patients in the ability to activate this part of the brain.
The children with CD compared to controls had abnormalities in another part of the brain, the temporal lobe, that is known to play a role in aggression, which is typical behaviour in these children.
The second study compared children with ADHD with those with OCD during a task of inhibition and saliency processing. Children with ADHD and those with OCD share inhibitory problems but have inverse problems with saliency processing. Saliency processing is dampened in ADHD children, leading to easy boredom, while it appears enhanced in patients with OCD. During saliency processing, children with ADHD had reduced activation in parts of the brain that are known to be important for attention processing (basal ganglia and the posterior cingulated), while children with OCD had enhanced activation in these regions. The strength of under- (ADHD) and over-activation (OCD) correlated with the respective severity of ADHD/OCD symptoms. The findings are in line with evidence for increased saliency processing in children with OCD and reduced saliency processing in children with ADHD and may be related to evidence for low/high levels of dopamine in the basal ganglia in ADHD/OCD, respectively. Dopamine is a neurotransmitter that mediates the perception of attention and is present in the basal ganglia. Both patient groups, however, shared abnormalities in medial frontal brain regions.
To read both papers in full, please follow the links:
Rubia, K, Halari, R, Cubillo, A, Mohammad, A-M, Scott, S, Brammer, M (2010) ‘Disorder-specific inferior prefrontal under-activation in boys with pure Attention-Deficit/Hyperactivity Disordercompared to boys with pure CD during cognitive flexibility’ Human Brain Mapping, in press: http://www3.interscience.wiley.com/cgi-bin/fulltext/123308786/PDFSTART
Rubia, K, Cubillo, A., Woolley, J, Brammer, MJ, Smith, AB (2010) ‘Disorder-specific dysfunctions in patients with Attention-Deficit/Hyperactivity Disorder compared to patients with Obsessive-compulsive disorder during interference inhibition and attention allocation’ Human Brain Mapping, in press: http://www3.interscience.wiley.com/journal/123469151/abstrac