Functional MRI-based intersubject correlations (ISCs) hold promise for studying the neural bases of ADHD’s heterogeneous symptoms in situations that reflect real-world difficulties, new research shows.
“The present results provide the first evidence of a connection between symptom scales and brain activity recorded when the participants have been involved in a situation that is similar to the ones where their difficulties typically occur,” wrote Juha Salmi, of the department of neuroscience and biomedical engineering at Aalto University in Espoo, Finland, and associates. The study was published in NeuroImage.
Many imaging studies in ADHD are too narrow and fail to reflect real-world situations and distractions, the investigators wrote. For the current study, the investigators conducted fMRI scans of participants in “cocktail party” situations. During fMRI, the participants viewed excerpts from the 2008 Finnish film “Three Wise Men,” in which three men were talking.
“There were periods when no additional distractors were presented and periods when the film was embedded with irrelevant distractors that the participants were told to ignore. The three different distractors (white noise, green; jazz music, red; speech, magenta) and nondistracted periods (blue) were presented in a pseudo-randomized order so that all other distractor types had to occur before the same distractor type was presented again,” the authors wrote. Each distractor lasted for 15 seconds.
The ISC approach sought to gauge how much neural networks in each group, 51 with ADHD and 29 without, “ticked together” – that is, synchronized and coordinated in a feature-specific manner.
As expected, across the film, ISCs of those in the ADHD group were weaker than were those in the control group in multiple brain areas, including the left precuneus, bilateral medial occipital cortices, left lateral occipital cortex, left temporoparietal junction, and medial and posterior parts of the left superior temporal cortex. Likewise, when the other distractors occurred – with the exception of constant white noise – weaker ISCs were found among the ADHD group. In fact, there were no brain regions in which healthy controls had weaker ISCs than did those with ADHD.
“ the investigators wrote. “At least theoretically, this approach could be used to identify neural patterns reflecting specific symptoms in complex, dynamic situations.”
One limitation of naturalistic studies is that the inferences are by their nature more general than they might be in more conventional, discrete experiments. Bridging the gap between naturalistic studies such as this one and other more conventional designs are needed, the investigators wrote, because dove-tailing their findings could provide significant insights.
The study was supported by the Academy of Finland and the Åbo Akademi University Endowment for the BrainTrain project. None of the authors have any biomedical financial interests or potential conflicts of interest.
SOURCE: Salmi J et al. Neuroimage. 2019 Nov 12. doi: 10.1016/j.neuroimage.2019.116352.