Scientists from the University of Helsinki led by Hamed Hakk discovered that adults with attention deficit hyperactivity disorder (ADHD) show more pronounced long-range temporal correlations - a measure reflecting how fluctuations in brain rhythms at one moment are related to fluctuations seconds or even minutes later. The work was published in the journal Translational Psychiatry.
The study involved 70 people: 36 neurotypical (mean age 34, 13 women) and 34 with diagnosed ADHD (mean age 37, 19 women). Brain activity was recorded using magnetoencephalography - a method that captures magnetic signals generated by the work of neurons. Participants performed two attention tasks: searching for faint images and responding to stimuli with response inhibition. They also completed questionnaires about ADHD symptoms and impulsivity.
It turned out that in the ADHD group, long-range correlations were stronger in the slow alpha range (8-13 Hz) during the detection task and in the fast gamma range (35-65 Hz) during the response task. These differences were not explained by age or overall rhythm intensity. In addition, in neurotypical participants, when moving from rest to the task, alpha correlations decreased widely, while in people with ADHD this almost did not happen; in the gamma range, on the contrary, correlations increased noticeably in the ADHD group.
The authors link the findings to the concept of brain criticality - the idea that the brain works best near the transition point between overly disconnected and excessively synchronized activity. According to the hypothesis, ADHD symptoms may reflect individual differences in exactly where the brain sits relative to this point. A moderate increase in excitability brings the brain closer to the critical point, where correlations are maximal, while a strong increase moves it into the region of excessive synchronization.
The study is correlational: it shows a statistical association but does not prove that features of brain activity cause ADHD symptoms. In addition, the sample was small, and participants with ADHD stopped taking medication 24 hours before testing, which could have influenced the results. The authors also note that long-range correlations can arise in systems far from the critical point, so the interpretation remains indirect.
Nevertheless, the work offers a new view of ADHD as a spectrum of states associated with brain dynamics and may stimulate further research.