Modern Presentations of ADHD in Terms of Frequency Bands in Quntitiative Electroencephalography (QEEG): The Modern Theoretical Approach

Attention-Deficit/Hyperactivity Disorder (ADHD) is the most common neurodevelopmental diorder and its worldwide frequency at school age is 5%. Impaired symptoms could be persist throughout the lifespan and diagnosed in 65% individuals received ADHD diagnosis in childhood. Both genetic and environmental factors play an important role, leading to alterations of multiple circuits in the brain and creating various pathways to symptoms, different individual deficit pro­files and resulting impairments. The Diagnostics and Statistical Handbook for Mental Disorders (DSM-5) defines three ADHD clinical phenotypes: attention difficulties, hyperactivity/impulsivity and the combined subtype. However, many studies have investigated the brain activity in ADHD patients compared with normal ones through electroencephalography so that underlying neurophysiology could be identified and examine the presentations regarding prognosis. Recently, a QEEG spectrum classification of ADHD population has been developed defining four main subtypes: I subtype (abnormal increase of delta-theta frequency range centrally or centrally-frontally), II subtype (abnormal increase of frontal midline theta rhythm), III subtype (abnormal increase of beta activity frontally), and IV subtype (excess of alpha activities at posterior, central, or frontal leads). Although this classification has been implied in various studies, comprehensive investigation is needed so that it could be established in diagnosis. The present review illuminates the theoretical and experimental basis of the QEEG spectrum classification of ADHD.