K.B.NG1, S.Y.LU1, T.J.GOH1
Institute of Mental Health1
Diagnosing ADHD in adults is challenging given the lack of objective assessment tools. We conducted a systematic literature review to examine existing neuroimaging evidence for functional differences and neuromarkers as potential objective indicators of adult ADHD.
A systematic search was conducted on Embase, ProQuest, PsycINFO, and PubMed databases using search terms adult attention deficit hyperactivity disorder AND diagnos* AND (functional neuroimag* OR functional magnetic resonance imaging OR electroencephalogram OR positron emission tomography) NOT (treat* OR interven*). Results yielded 508 unique peer-reviewed articles published between January 2016 and June 2021 (inclusive). 9 other articles were shortlisted through citation searches. Screening abstracts identified 76 articles, 38 of which met the following inclusion criteria: 1) functional measures utilized for ADHD assessment, 2) involves adult ADHD participants (≥18 years), 3) includes neurotypical control group.
Overall, 20 articles utilized electroencephalography (EEG), 17 studied functional magnetic resonance imaging (fMRI), and 1 employed transcranial doppler sonography. Multiple brain regions during resting-state, attentional, emotional-response, reward-response, or sensory tasks highlighted potential task-based and resting-state differences between ADHD adults and controls across functional neuroimaging modalities. Candidate neuromarkers identified using fMRI, EEG power, and event-related potentials reported sensitivity and specificity of 60.0 to 95.0% and 46.7 to 95.0% respectively.
Given the diverse tasks and brain regions investigated across studies, no definitive conclusions can be drawn. While fMRI and EEG may identify potential neuromarkers, replication of existing studies’ paradigms is needed to increase consistency and agreement concerning resting-state and task-based neural activity and activation patterns in adult ADHD.