Attention deficit hyperactivity disorder (ADHD) may be caused by disruption to brain signals that are involved in cognitive control. A link between this disruption and ADHD was previously made in children and has now been shown in young adults, improving researchers’ understanding of what could be behind the condition.
ADHD affects a person’s behaviour, with symptoms including hyperactivity and inattention. at King’s College London and her colleagues have previously shown that . These signals can be used as a measure of someone’s degree of cognitive control, which helps them stay on task when potential distractions are present, says McLoughlin.
She and a different team of colleagues wanted to find out if this disrupted brain signalling also occurred in adults with ADHD. They therefore used an electroencephalogram to scan the brains of 283 pairs of identical twins, aged between 21 and 23 years old, as they were put through several cognitive tests.
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The participants are part of a long-running twin study and have been monitored since birth, giving the researchers behavioural data going back to their childhoods. By studying identical twins, the researchers could estimate how much of the disrupted brain signalling could be attributed to their genetic variations rather than their environment.
Of the 566 participants, 111 adults met the criteria for ADHD, as diagnosed by the researchers via a standard test. In some twin pairs, both qualified for such a diagnosis, while in others only one individual was diagnosed and in some there were no diagnoses at all.
The researchers found that those who they diagnosed with ADHD were more likely to have these disrupted brain signals than those who they hadn’t diagnosed, mirroring the finding previously made in children with ADHD. The adults who had this disrupted signalling were also more likely to have shown ADHD symptoms when they were children. “ADHD symptoms in childhood predict brain function later in life,” says McLoughlin. “It all seems to be related across the lifespan.” The researchers didn’t investigate whether these adults were more likely to have been diagnosed with ADHD as a child.
The team also identified a genetic overlap between having ADHD symptoms in childhood and being diagnosed with the condition as an adult. Overall, the findings will help researchers to better understand the neurology of the condition, which could then lead to new treatments for any adverse ADHD symptoms, says McLoughlin.
However, the relatively small study doesn’t show how widespread this disrupted brain signal is in people with ADHD, nor does it reveal whether this is the condition’s cause. “It could be the case that the same genes cause [disrupted] midline theta frontal signals and cause ADHD but they’re not causally related,” says McLoughlin.
Nevertheless, if a link is confirmed with further testing, reducing the variability in this disrupted brain signal could help to treat ADHD, she says. But as ADHD isn’t a life-threatening condition, this variability would ideally be reduced via a non-invasive procedure, which may not be possible, she says.
at Oxford Brookes University, UK, says it is unlikely that just one factor causes ADHD, but studies like these that collect data from the same people over a long period of time allow researchers to make links between genes that influence brain signalling and ADHD-associated behaviours over time. “Links between these factors can help us to start to understand differences between individuals and allow us to target specific processes and pathways that contribute to these differences.”
Biological Psychiatry
Article amended on 3 August 2023
This article has been changed to correct the number of participants in the study.
