Electroencephalogram θ/β Ratio and Arousal in Attention-Deficit/Hyperactivity Disorder: Evidence of Independent Processes

BackgroundFor nearly 20 years, the θ/β power ratio in the electroencephalogram (EEG) has been used within the attention-deficit/hyperactivity disorder (ADHD) literature as a marker of central nervous system (CNS) arousal, underpinning current models of the disorder. However, this usage has not been validated. We aimed to directly test the θ/β ratio as a marker of arousal within this population.MethodsResting state EEG activity was investigated as a function of CNS arousal in two age-matched groups of boys (each n = 30), with and without ADHD. Arousal was defined in terms of skin conductance level (SCL), which has a long history as a measure of CNS arousal.ResultsRelative θ power and the θ/β ratio were elevated, and SCL and relative α and β power were reduced, in the ADHD group compared with control subjects. In both groups, mean α level correlated negatively with SCL. There was no significant correlation between the θ/β ratio and SCL.ConclusionsThese data contradict the supposed linkage between the θ/β ratio and arousal in ADHD, confirming previous results from normal children. They suggest the need for reevaluation of current models of the disorder and reconceptualization of existing EEG data from both normal and atypical populations.