ADHD traits may reflect where each brain sits on a spectrum of activity, small study suggests

How strongly adults show ADHD traits may depend on where each person’s brain sits on a range of activity patterns. It may not come down to a simple divide between people who have ADHD and people who don’t. That is the suggestion of a small brain-imaging study published in Translational Psychiatry in July and reported by PsyPost this week.

The research was led from the University of Helsinki. Several authors also work at the University of Glasgow, and one at the University of Birmingham.

What the researchers looked at

The study uses an idea called ‘brain criticality’. Brain activity can run anywhere from loosely coordinated to tightly synchronised. The theory says the brain works most flexibly near the tipping point between the two.

The team couldn’t measure that point directly. Instead they measured ‘long-range temporal correlations’, which show how far the rhythm of brain activity at one moment echoes seconds or even minutes later. These echoes are thought to be strongest near the tipping point, so they work as an indirect marker.

70 adults took part: 34 with an existing ADHD diagnosis and 36 without. Their brain activity was recorded using magnetoencephalography (MEG), a scanner that picks up the tiny magnetic signals made by brain activity. They were recorded at rest and during two attention tasks. In one they spotted faint images. In the other they responded to one kind of picture and held back from responding to another. Everyone also filled in questionnaires about ADHD traits and impulsivity.

What they found

On most measures, the two groups did the tasks equally well. According to PsyPost, people with ADHD more often responded when they were meant to hold back. There was no difference in how much reaction times varied, even though that measure is often linked with ADHD.

On average, the ADHD group showed stronger long-range correlations in some brain rhythms during the tasks. Across all 70 people, the link with questionnaire scores depended on the task and the rhythm. In one fast rhythm, stronger correlations went with higher scores. In another, they peaked in people with middling scores. The researchers interpret this to mean that people sit at different points in the brain’s operating range. In their reading, the highest scores reflect a shift towards the more synchronised end.

PsyPost reports that the researchers also speculated that moderate ADHD traits might sometimes be an advantage, pointing to research on hyperfocus and novelty-seeking. Crucially, no single brain pattern neatly sorted people into ‘ADHD’ and ‘not ADHD’. Individual differences were wide.

The authors sum up their aim like this:

“Our study thus proposes a novel complex systems-level framework to explain the emergence of ADHD symptoms and their continuum across the population.”

A note on the language

The paper and the coverage use clinical, deficit-based terms: ‘symptoms’, ‘severity’, ‘overly synchronised’. Here ‘overly’ describes one end of a theoretical scale. It is not evidence that ADHD brains are broken. The study measured lab tasks and questionnaire scores, not people’s lives, strengths or the support around them. Its central finding, that ADHD traits vary along a continuum, fits a difference-based view better than its vocabulary does.

The limits

The researchers and PsyPost list several caveats:

• The study is small and correlational, so it can’t show that these brain patterns cause anything.
• People with other psychiatric or neurological conditions were left out, so the results may not reflect the full range of ADHD adults.
• As part of the study design, participants with ADHD paused their usual medication for 24 hours before testing, so the recordings may not reflect a typical day for them.
• The results varied by task and rhythm. An earlier study of resting brain recordings found no such differences in ADHD adults.
• These correlations can occur in systems that aren’t near a tipping point, so the criticality explanation remains indirect.

The journal notes that the published version is an early, accepted version of the paper and may still be edited before the final record replaces it.

This piece summarises reporting by PsyPost and the original paper in Translational Psychiatry (Springer Nature). Read the original articles for the full story.