MEG event-related desynchronization and synchronization deficits during basic somatosensory processing in individuals with ADHD

Neurosciences and Mental Health Program, The Hospital for Sick Children, Toronto, Canada. .
Behavioral and Brain Functions (Impact Factor: 2). 02/2008; 4:8. DOI: 10.1186/1744-9081-4-8
Source: PubMed

ABSTRACT Attention-Deficit/Hyperactivity Disorder (ADHD) is a prevalent, complex disorder which is characterized by symptoms of inattention, hyperactivity, and impulsivity. Convergent evidence from neurobiological studies of ADHD identifies dysfunction in fronto-striatal-cerebellar circuitry as the source of behavioural deficits. Recent studies have shown that regions governing basic sensory processing, such as the somatosensory cortex, show abnormalities in those with ADHD suggesting that these processes may also be compromised.
We used event-related magnetoencephalography (MEG) to examine patterns of cortical rhythms in the primary (SI) and secondary (SII) somatosensory cortices in response to median nerve stimulation, in 9 adults with ADHD and 10 healthy controls. Stimuli were brief (0.2 ms) non-painful electrical pulses presented to the median nerve in two counterbalanced conditions: unpredictable and predictable stimulus presentation. We measured changes in strength, synchronicity, and frequency of cortical rhythms.
Healthy comparison group showed strong event-related desynchrony and synchrony in SI and SII. By contrast, those with ADHD showed significantly weaker event-related desynchrony and event-related synchrony in the alpha (8-12 Hz) and beta (15-30 Hz) bands, respectively. This was most striking during random presentation of median nerve stimulation. Adults with ADHD showed significantly shorter duration of beta rebound in both SI and SII except for when the onset of the stimulus event could be predicted. In this case, the rhythmicity of SI (but not SII) in the ADHD group did not differ from that of controls.
Our findings suggest that somatosensory processing is altered in individuals with ADHD. MEG constitutes a promising approach to profiling patterns of neural activity during the processing of sensory input (e.g., detection of a tactile stimulus, stimulus predictability) and facilitating our understanding of how basic sensory processing may underlie and/or be influenced by more complex neural networks involved in higher order processing.

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    • "Magnetoencephalography (MEG) measures the spatial and temporal aspects of brain activity. As a result, studies frequently use both ERP and MEG to evaluate the activity in a specific brain region in response to an event [56] . Studies have found impairments in various areas associated with attention in individuals with ADHD. "
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    • "However , these oscillations may play a role in attention as increases in sensorimotor beta power correlate with attention directed toward a motoric event (Muthukumaraswamy and Singh, 2008) and improved sensorimotor performance (Egner and Gruzelier, 2004; Egner et al., 2004; Vernon et al., 2003). Interestingly, individuals with attention-deficit/hyperactivity disorder show diminished sensorimotor beta response to somatosensory input (Dockstader et al., 2008). "
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    • "Ello sugiere que la existencia de alteraciones en funciones relacionadas con la percepción de estímulos simples y la anticipación a los mismos influye en la disfunción a más alta escala. Recientemente, Dockstader et al. (2008) han publicado unos datos recogidos con MEG referentes a la diferencia de percepción de estímulos somatosensoriales predecibles frente a estímulos no predecibles en adultos con TDAH, concluyendo que existe una alteración en el procesamiento somatosensorial en los casos con TDAH frente a los controles. Con estas investigaciones se ahonda no sólo en las múltiples formas de disfunción, sino en las múltiples fuentes de disfunción del TDAH. "
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