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Attention-deficit/hyperactivity disorder (ADHD) was found to be characterized by a deviant pattern of electrocortical activity during resting state, particularly increased theta and decreased beta activity.
The first objective of the present study is to confirm whether individuals with slow alpha peak frequency contribute to the finding of increased theta activity in ADHD. The second objective is to explore the relation between resting-state brain oscillations and specific cognitive functions. From 49 boys with ADHD and 49 healthy control boys, resting-state EEG during eyes open and eyes closed was recorded, and a variety of cognitive tasks were administered. Theta and beta power and theta/beta ratio were calculated using both fixed frequency bands and individualized frequency bands. As expected, theta/beta ratio, calculated using fixed frequency bands, was significantly higher in ADHD children than control children. However, this group effect was not significant when theta/beta ratio was assessed using individualized frequency bands. No consistent relation was found between resting-state brain oscillations and cognition. The present results suggest that previous findings of increased theta/beta ratio in ADHD may reflect individuals with slow alpha peak frequencies in addition to individuals with true increased theta activity. Therefore, the often reported theta/beta ratio in ADHD can be considered a non-specific measure combining several distinct neurophysiological subgroups such as frontal theta and slowed alpha peak frequencies.
Future research should elucidate the functional role of resting-state brain oscillations by investigating neurophysiological subgroups, which may have a clearer relation to cognitive functions than single frequency bands.
Lansbergen MM, et al, The increase in theta/beta ratio on resting-state EEG in boys with attention-deficit/
hyperactivity disorder is mediated…, Prog Neuro-Psychopharmacol Biol Psychiatry (2010), doi:10.1016/j.pnpbp.2010.08.004. The full article available for purchase online @ http://www.sciencedirect.com
Is that true theta, or really just slowed alpha?
The theta/beta ratio is derived from published studies which defined the bands a bit differently than some would, as the theta band goes from 4 Hz up to 8 Hz, with beta defined as from 13-21 Hz. This ratio was calculated for eyes open conditions at the Cz electrode site in the Monastra et al study from 1999. Theta is seldom clinically defined up to 8 Hz, as it is generally seen as a rhythm between 4 and 7 Hz, commonly peaking at 5-6 Hz for the rhythm. The thalamo-cortical-thalamic “alpha” rhythm is known to be able to slow to as low as 3-4 Hz, and accelerate up to 15 or 16 Hz at the extremes of the band, though in most adults it is from 7-13 Hz, and commonly is specified at 8-12 Hz as a “standard band”. Most modern neuroscientists use the individual alpha frequency (IAF), and do not rely on pre-defined bands.
When the theta/beta ratio was first promoted, many were surprised at the sensitivity to ADHD that this metric had at better than 95%. Over the years, others have seen individual cases of ADHD where the theta was not actually elevated, or the beta was not really low, and clinically the training the ratio of theta to beta did not work with as good an efficacy as one might have hoped for. Given the “diagnostic sensitivity”, one would hope for a more predictable treatment outcome.
Since the 1999 paper, many other findings have been reported, and some even have challenged the very use of the DSM category. Following the publication in 2005 of the EEG phenotype paper, a study on prediction of stimulant medication effect in ADHD was undertaken to prospectively test the predictive power of the retrospectively derived categories from the phenotype paper.
The frontal slow variant was stimulant responsive, as predicted, though the study also showed that there was a slower alpha variant that would have triggered the “theta” calculation of the standardized theta/beta metric. This slow alpha is not stimulant responsive like the cases with frontal theta, and the theta and slow alpha have totally different pathophysiology causing their presence.
Modern neuroscientists have looked at this phenomenon, and now there is a paper that speaks directly to this. In the 2010 Elsevier Press textbook: Progress in Neuro-Psychopharmacology & Biological Psychiatry, there is a chapter on this topic which is rather dismissive of the prognostic utility of the Theta/beta ratio… the chapter title is: The increase in theta/beta ratio on resting-state EEG in boys with attention-deficit/hyperactivity disorder is mediated by slow alpha peak frequency. The journal article authors are all researchers from the Netherlands: Marieke M. Lansbergen, Martijn Arns, Martine van Dongen-Boomsma, Desirée Spronk and Jan K. Buitelaar.
They conclude: “The present results suggest that previous findings of increased theta/beta ratio in ADHD may reflect individuals with slow alpha peak frequencies in addition to individuals with true increased theta activity. Therefore, the often reported theta/beta ratio in ADHD can be considered a non-specific measure combining several distinct neurophysiological subgroups such as frontal theta and slowed alpha peak frequencies.”
I have to agree with their conclusion. Individualizing the approach avoids the standardization of bands, and understanding the pathophysiology of the EEG pattern is important to designing an effective NF or medication approach to the individual client.