Resting state EEG and symptoms of ADHD
Centre for Psychophysics, Psychophysiology, and Psychopharmacology, University of Wollongong, Wollongong, Australia Brain & Behaviour Research Institute, University of Wollongong, Wollongong, Australia School of Psychology, University of Wollongong, Wollongong, Australia We regard resting-state EEG as reflecting the dynamic potential of the brain's current functional state — it provides the substrate of all cognitive and perceptual processing. Our research program on the electrophysiology of AD/HDhas been ongoing for some 20 years, andwe have examined resting-state EEG power and coherence, aswell as ERPs, in AD/HD patients, ranging across children, adolescents, and adults. This presentation covers some of those studies, concentrating on restingstate EEG power and coherence in children. In relation to power studies, it iswell-established that childrenwith AD/HD showglobally-enhanced absolute delta and theta power, globally-reduced absolute alpha and beta power, and elevated theta/beta ratio. In relative power terms, globally elevated theta and reduced alpha and beta are observed, with fronto-central reductions in delta. All these anomalies are more extensive in children with the combined type of AD/HD, compared with the inattentive type, so these anomalies clearly relate to some extent with hyperactivity. In separate studies we have found significant positive correlations of scores on the Connors' Inattention scale with global absolute theta and frontal relative theta, and negative correlations with absolute gamma power. Further, scores on the Connors' Hyperactivity–Impulsivity scale have been correlated positively with the theta/beta ratio. That is, deviant EEG power profiles have been positively associated with the dominant symptoms of AD/HD. With resting-state EEG coherence, AD/HD is associated with elevated intrahemispheric coherences at shorter inter-electrode distances in theta, and reduced lateral differences in theta and alpha. At longer interelectrode distances, patients have reduced intra-hemispheric alpha coherences. With inter-hemispheric electrode pairs, children with AD/ HD have frontal coherences elevated in delta and theta, and reduced in alpha. Temporal coherence is reduced in alpha, and central/parietal/ occipital coherence is enhanced in theta. In relation to EEG coherence and symptoms,we have reported that reduced left-lateralised coherences across delta, alpha, beta, and gamma bands correlate negatively with Inattention scores, while reduced frontal inter-hemispheric coherences correlate negatively with hyperactivity–impulsivity scores. These negative correlations between anomalous coherences and symptoms suggest the involvement of compensatory processes. Future studies may provide more understanding of the brain dysfunctions involved in AD/HD by pursuing such EEG anomaly/symptom linkages across a wide age-range.