In a Belgian study, functional magnetic resonance imaging (fMRI) indicated that attenuated down-regulation of the default mode network (DMN) in the brain during task switching in adults with ADHD does not explain excess DMN activity during goal-directed tasks. Instead, DMN re-activation is suggested to be impaired compared with adults without ADHD.
The aim of this study was to investigate whether the excess levels of DMN activity during task performance associated with ADHD are related to: 1) attenuated down-regulation of the DMN during rest-to-task switching; and/or 2) dysfunction of the right anterior insula (rAI), a brain region thought to be involved with state switching. Adults with ADHD (n=19) and without ADHD (n=21) undertook a novel state-to-state switching paradigm, with experimental tasks performed inside a fMRI scanner to acquire whole brain functional images.
Although no differences were observed in terms of error rate between the ADHD and control groups with the state-to-state switching experimental tasks (p=0.09), a significantly slower response time was observed in all conditions (including task switch, rest to task, and task repeat: p=0.004 overall) in adults with ADHD compared with adults without ADHD. Anticipatory DMN down-regulation was not impaired in adults with ADHD when switching from rest to task compared with adults without ADHD (p=0.942). However, DMN up-regulation was delayed in adults with ADHD compared with adults without ADHD when switching from task to rest (p=0.006). Additionally, rAI activation was consistently reduced in all switch tasks in the ADHD group (p=0.013).
The evidence from this relatively small sample indicates that rest-to-task DMN attenuation seems to be intact in adults with ADHD, although DMN up-regulation appears to be impaired when switching back to rest. The authors propose that perhaps maintenance of DMN suppression may instead be the cause of attention issues.
Read more about DMN status during task switching here
Sidlauskaite J, Sonuga-Barke E, Roeyers H, et al. Default mode network abnormalities during state switching in attention deficit hyperactivity disorder. Psychol Med 2016; 46: 519-528.