Brain differences in children with ADHD

This post was written by Margarita Kanevski and Sinead Rhodes

A few weeks ago we spoke about the media coverage of Richard Bacon’s diagnosis of ADHD. A second ADHD related story was covered in the media within the same timeframe. The headline ‘ADHD sufferers have smaller brains’ and ‘Children with ADHD have smaller brain size, study says’  appeared in the news. These headlines relate to recent findings that 4-5-year-old pre-schoolers who showed ADHD symptoms had lower cortical volume than children without signs of ADHD.  So what is the evidence behind the headlines?

What did the study do?

The study initially involved 129 4-5-year-old children recruited from the community, nurseries and paediatric offices. Parents were asked to complete various reports about their child’s behaviour using interviews and questionnaires.  Based on this, children were assigned to either (1) an ADHD group, or (2) a typically developing group. In the final groups, there were 52 children in the ADHD group and 38 controls (90 had usable MRI scans).  Both groups were comparable on gender, age, race, IQ, language abilities and parent education and occupation.

Children were then assessed on their language and attention, and they undertook a brain imaging (Magnetic Resonance Imaging/MRI) scan. MRI is a brain imaging technique that uses magnetic waves to create a detailed 3D image of the brain.  Using these scans, the researchers calculated inner and outer brain surfaces, total cerebral volume and volume in specific brain regions.  Results of the study showed that children in the ADHD group had lower grey matter volume in areas of the brain known as the frontal, parietal and temporal lobes than the typically developing group, and these irregularities were linked with ADHD symptom severity. The brain regions have been strongly linked with processes involved in controlling behaviour (known as executive functions).

A few things to bear in mind…

To qualify for the “ADHD group” the child had to score below a specific score on a behavioural questionnaire (based on parent responses), have had symptoms for at least 6 months (based on parent interviews) and show impairments across various situations (again, as per parent reports). Note that at no stage was a formal examination conducted by a clinician, which is key to providing an accurate diagnosis. This means that an ADHD diagnosis in this study was based solely on parental reports and not corroborated by a teacher which is an essential part of the diagnostic process. This is problematic, as parents who already feel that their child might have some behavioural problems could potentially have provided biased answers to affirm a diagnosis. Additionally, the young age of the participants (4-5 years) means that we need to be particularly cautious to infer the child would eventually receive a formal diagnosis of ADHD.

Although the study found lower volume in brain regions associated with executive functions, when we look more broadly at research in this area, less than half of children with ADHD actually show difficulties with this process. This implies that we cannot generalise these findings to every child with ADHD. Additionally, the researchers did not find volume reductions in the cingulate cortex – an important brain region that is consistently linked with ADHD.

Despite its limitations, the study adds to our knowledge of brain differences in children reported to show ADHD-like symptoms early on in childhood. It is important though to take a step back and reflect on the potential stigma carried by bigger-smaller brain “neuromyths”, and thoroughly consider the evidence behind them.