Biophysical modeling of tonic cortical electrical activity in attention deficit hyperactivity disorder

Westmead Hospital, Sydney, New South Wales, Australia
International Journal of Neuroscience (Impact Factor: 1.52). 10/2005; 115(9):1273-305. DOI: 10.1080/00207450590934499
Source: PubMed


Psychophysiological theories characterize Attention Deficit Hyperactivity Disorder (ADHD) in terms of cortical hypoarousal and a lack of inhibition of irrelevant sensory input, drawing on evidence of abnormal electroencephalographic (EEG) delta-theta activity. To investigate the mechanisms underlying this disorder a biophysical model of the cortex was used to fit and replicate the EEGs from 54 ADHD adolescents and their control subjects. The EEG abnormalities in ADHD were accounted for by the model's neurophysiological parameters as follows: (i) dendritic response times were increased, (ii) intrathalamic activity involving the thalamic reticular nucleus (TRN) was increased, consistent with enhanced delta-theta activity, and (iii) intracortical activity was increased, consistent with slow wave (<1 Hz) abnormalities. The longer dendritic response time is consistent with the increase in the activity of inhibitory cells types, particularly in the TRN, and therefore reduced arousal. The increase in intracortical activity may also reflect an increase in background activity or cortical noise within neocortical circuits. In terms of neurochemistry, these findings may be accounted for by disturbances in the cholinergic and/or noradrenergic systems. To the knowledge of the authors, this is the first study to use a detailed biophysical model of the brain to elucidate the neurophysiological mechanisms underlying tonic abnormalities in ADHD.

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Available from: Donald L Rowe, Mar 12, 2014
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    • "The increased ratios of the resting slow/fast band EEG activity such as theta/alpha ratio have thus been related to risky decision-making or impulsivity. Additionally, a larger theta/alpha ratio can be viewed from the following two perspectives: low power in fast oscillations (e.g., alpha) has been associated with reduced executive functioning and self-control underlying the hypo-arousal model of ADHD (Rowe et al., 2005), whereas high power in slow oscillations (e.g., theta) has been related to a maturational delay reflected in a diminished inhibition of subcortical drives and impulses (Schutter, Leitner, Kenemans, & van Honk, 2006). From a general perspective, the finding of an association between better power fitness and less deviant brain oscillation in ADHD children is consistent with previous studies. "
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    ABSTRACT: Children with attention deficit hyperactivity disorder (ADHD) are characterized by a deviant pattern of brain oscillations during resting state, particularly elevated theta power and increased theta/alpha and theta/beta ratios that are related to cognitive functioning. Physical fitness has been found beneficial to cognitive performance in a wide age population. The purpose of the present study was to investigate the relationship between physical fitness and resting-state electroencephalographic (EEG) oscillations in children with ADHD. EEG was recorded during eyes-open resting for 28 children (23 boys and 5 girls, 8.66 +/- 1.10 years) with ADHD, and a battery of physical fitness assessments including flexibility, muscular endurance, power, and agility tests were administered. The results indicated that ADHD children with higher power fitness exhibited a smaller theta/alpha ratio than those with lower power fitness. These findings suggest that power fitness may be associated with improved attentional self-control in children with ADHD.
    Full-text · Article · Jan 2015 · Journal of Psychophysiology
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    • "Lower resting alpha observed in ADHD individuals has been proposed to relate to problems in attentional selfcontrol (Woltering, Jung, Liu, & Tannock, 2012). These individuals may over-activate their neural circuit for processing external stimuli during a relaxing state, which may be associated with a lack of inhibition over sensory input (Rowe et al., 2005). Importantly, physical activity is found to improve executive function via improving the allocation of attentional resources during information processing. "
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    ABSTRACT: Objective: This study attempted to determine whether the effects of physical exercise were reflected in the resting electroencephalographic (EEG) pattern of ADHD children. Method: Thirty-two ADHD children were assigned to either an exercise group or a control group. The exercise group participated in a water aerobics program for 8 weeks, whereas no intervention was administered to the control group. Resting EEGs were recorded under open-eyes condition before and after the intervention. Data from eligible participants, 15 from the exercise group (11 boys and 4 girls, 7.93 ± 1.02 years) and 14 from the control group (14 boys, 8.27 ± 1.04 years), were further analyzed. Results: While controlling for the baseline resting EEG, separate ANCOVAs indicated that the exercise group showed smaller theta/alpha ratios over the frontal and central brain sites after the intervention compared with the control group. Conclusion: This finding suggests that aerobic exercise may enhance the cognitive functions of children with ADHD, as reflected in resting EEG.
    Full-text · Article · Oct 2014 · Journal of Attention Disorders
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    • "Similar abnormalities in EEG power have been observed in patients with head injuries, dementia, and schizophrenia [16,18,19], indicating a more general atypical neural functioning or organization. The EEG profile seen with ADHD has been interpreted in various ways: the relatively low power in fast oscillations is consistent with the cortical hypo-arousal theory giving rise to reduced executive functioning and self-control [20], whereas the high power in slow oscillations could reflect diminished control of strong subcortical drives and impulses [21]. Another perspective builds on work showing that, compared to normally developing children, children with ADHD display a neural oscillatory pattern that resembles younger children [22], providing support for the maturational lag model of ADHD which explains their symptoms as being developmentally inappropriate [23]. "
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    ABSTRACT: Background Among the most robust neural abnormalities differentiating individuals with Attention-Deficit/Hyperactivity Disorder (ADHD) from typically developing controls are elevated levels of slow oscillatory activity (e.g., theta) and reduced fast oscillatory activity (e.g., alpha and beta) during resting-state electroencephalography (EEG). However, studies of resting state EEG in adults with ADHD are scarce and yield inconsistent findings. Methods EEG profiles, recorded during a resting-state with eyes-open and eyes-closed conditions, were compared for college students with ADHD (n = 18) and a nonclinical comparison group (n = 17). Results The ADHD group showed decreased power for fast frequencies, especially alpha. This group also showed increased power in the slow frequency bands, however, these effects were strongest using relative power computations. Furthermore, the theta/beta ratio measure was reliably higher for the ADHD group. All effects were more pronounced for the eyes-closed compared to the eyes-open condition. Measures of intra-individual variability suggested that brains of the ADHD group were less variable than those of controls. Conclusions The findings of this pilot study reveal that college students with ADHD show a distinct neural pattern during resting state, suggesting that oscillatory power, especially alpha, is a useful index for reflecting differences in neural communication of ADHD in early adulthood.
    Full-text · Article · Dec 2012 · Behavioral and Brain Functions
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