Cortical excitability in adult patients with attention-deficit/hyperactivity disorder (ADHD)

doi:10.1016/j.neulet.2007.04.024

Neuroscience Letters

Volume 419, Issue 2, 29 May 2007, Pages 137-141

https://doi.org/10.1016/j.neulet.2007.04.024 Get rights and content

Abstract

Attention-deficit/hyperactivity disorder (ADHD) is more and more focused on, and the awareness of adult patients with ADHD increases. Deficits in inhibitory processes in cortical brain areas are discussed as possible causes for ADHD. An easy measurement of these processes is provided by transcranial magnetic stimulation (TMS). We applied single- and double-pulse TMS to the left motor cortex while an electromyogram (EMG) was taken at the abductor pollicis brevis muscle (APB) of the right hand. Intracortical inhibition (SICI) and facilitation (ICF) were measured in ten adult ADHD patients and ten healthy participants using inter-pulse intervals of 2 and 3 ms (SICI), and 8 and 15 ms (ICF). Furthermore, resting motor threshold (RMT) and latency of the motor evoked potential (MEP) following magnetic stimulation were compared. t-Tests were calculated for statistical analysis. TMS measurements resulted in impaired inhibition in ADHD patients, whereas there were no differences in facilitation, RMT and MEP-latency between groups. Large variability in the patient group was found. This study expands the findings of deficits in inhibition described in earlier studies in children to an adult population, which could be a hint for similar neurophysiological mechanisms underlying ADHD symptomatology in children and adults.

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Acknowledgements

The authors wish to thank Kathrin C. Zierhut, Melanie Harder and Ramona Taeglich for their support. This study was supported by a grant of the Deutsche Forschungsgemeinschaft (German research community), KFO 125/1-1.

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Citation Excerpt :
Only one study investigated LICI in SCZ, and found no difference when compared to HC (Fitzgerald et al., 2003). Reduced SICI in both child and adult patients suffering from ADHD has been reported in most (Gilbert et al., 2011; Hoegl et al., 2012; Richter et al., 2007; Schneider et al., 2007; Wu et al., 2012), although not all (Hasan et al., 2013; Hoeppner et al., 2008a), TMS studies. Only three studies measured CSP between child ADHD and HC and found no difference (Buchmann et al., 2003; Gilbert et al., 2011; Wu et al., 2012), whereas two studies of CSP in adult ADHD yielded inconclusive evidence (Hasan et al., 2013; Hoeppner et al., 2008b), Table 1.
Characterizing the neurobiology of schizophrenia and other major psychiatric disorders is one of the main challenges of the current research in psychiatry. The availability of Transcranial Magnetic Stimulation (TMS) allows to directly probe virtually any cortical areas, thus providing a unique way to assess the neurophysiological properties of cortical neurons. This article presents a review of studies employing TMS in combination with Motor Evoked Potentials (TMS/MEPs) and high density Electroencephalogram (TMS/hd-EEG) in schizophrenia and other major psychiatric disorders. Studies were identified by conducting a PubMed search using the following search item: “transcranial magnetic stimulation and (Schizophrenia or OCD or MDD or ADHD)”. Studies that utilized TMS/MEP and/or TMS/hd-EEG measures to characterize cortical excitability, inhibition, oscillatory activity, and/or connectivity in psychiatric patients were selected. Across disorders, patients displayed a pattern of reduced cortical inhibition, and to a lesser extent increased excitability, in the motor cortex, which was most consistently established in Schizophrenia. Furthermore, psychiatric patients showed abnormalities in a number of TMS-evoked EEG oscillations, which was most prominent in the prefrontal cortex of Schizophrenia relative to healthy comparison subjects. Overall, results from this review point to significant impairments in cortical excitability, inhibition, and oscillatory activity, especially in frontal areas, in several major psychiatric disorders. Building on these findings, future studies employing TMS-based experimental paradigms may help elucidating the neurobiology of these psychiatric disorders, and may assess the contribution of TMS-related measures in monitoring and possibly maximizing the effectiveness of treatment interventions in psychiatric populations.

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Cortical excitability in adult patients with attention-deficit/hyperactivity disorder (ADHD)

Abstract

Section snippets

Acknowledgements

Neurosci. Lett.

Clin. Neurophysiol.

Biol. Psychiatry

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Clin. Neurophysiol.

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Compr. Psychiatry

Biol. Psychiatry

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Clin. Neurophysiol.

Electroencephalogr. Clin. Neurophysiol.

Diagnostic and Statistical Manual of Mental Disorders