Neurophysiological biomarkers in children with attention deficit hyperactivity disorders using non-invasive evaluations of brain function

Abstract

The prevalence of children with attention deficit hyperactivity disorder (ADHD) appears to be increasing in Japan. Establishment of standardized diagnostic methods and approaches to the treatment of ADHD is therefore imperative. In general, ADHD is behaviorally diagnosed with behavioral questionnaires as a rating scale because objective biomarkers for ADHD remain elusive. For ADHD children, objective biomarkers must be simple, definitive, and definable using non-invasive evaluations. In recent years, neurophysiological findings with non-invasive evaluations of brain function have been reported for ADHD. Herein I review non-invasive evaluations of brain function for ADHD, with a particular focus on frequency analysis of electroencephalograms (EEGs), event-related potentials (ERPs), and near-infrared spectroscopy (NIRS). In resting EEGs, the rate of power spectra as measured by delta/beta was increased in ADHD children. Attempts have been made to apply the delta/beta ratio to the diagnosis of ADHD, and this approach has positive and negative aspects. ERPs such as P300, NoGo potentials, and mismatch-negativity (MMN) have reportedly shown utility in diagnosis and evaluation of treatment for ADHD children. NIRS is easy to perform at the forehead and is suitable for analysis of frontal functions in children. As a result, numerous studies have reported frontal dysfunctions in ADHD children. These data suggest that hemodynamic and electrophysiological findings might be useful as biomarkers in ADHD children. In the future, these methods are likely to be applicable as adjunctive methods for diagnosis and evaluation of therapy.