Research ReportSpontaneous magnetoencephalographic activity in patients with obsessive-compulsive disorder
Introduction
Obsessive-compulsive disorder (OCD) is the world's fourth most common mental disorder and has a lifetime prevalence of 2–3% (Weissman et al., 1994). OCD is characterized by recurrent, intrusive and distressing thoughts (obsessions) or repetitive behaviors (compulsions) (Stein, 2002). The underlying pathophysiology is still not fully understood. Recently, advances in neuroimaging techniques have led to a better understanding of brain–behavior relationships in OCD. Most data derive from positron emission tomography (PET), functional magnetic resonance imaging (fMRI) and single photon emission tomography (SPECT) studies (Adler et al., 2000, Saxena and Rauch, 2000, Rauch et al., 2001, Kwon et al., 2003, Whiteside et al., 2004, Nakao et al., 2005). These studies demonstrated over- or underactivity of frontal cortices (mainly orbito-frontal and dorsolateral prefrontal cortices; OF and DLPFC) and parts of the basal ganglia when the resting state was compared with controls (Saxena and Rauch, 2000, Whiteside et al., 2004). Symptom provocations in OCD patients using experimental paradigms have also been found to generate activations in similar brain areas (Adler et al., 2000, Nakao et al., 2005). Finally, when pharmacotherapy or behavioral therapy was employed, activations in OF, DLPFC and basal ganglia were found to be reduced (Schwartz et al., 1996, Brody et al., 1999, Saxena and Rauch, 2000). Therefore, these studies indicate that OCD symptoms might be mediated by a hyperactivity in orbito-frontal and subcortical circuits, which may finally lead to an imbalance of tone between direct and indirect striato-pallidal pathways (Saxena and Rauch, 2000, Rauch et al., 2001). Basically, spontaneous brain activity may also be investigated by magnetoencephalography (MEG). MEG is an additional neuroimaging method that combines both high temporal and spatial resolution. It represents neuronal activity more directly than techniques using intermediates like changes in cerebral blood flow or glucose metabolism. Since magnetic fields are not distorted by the different conduction of the skull and other inhomogenities of the head, MEG is a potentially powerful localization tool of brain function. Measurements of spontaneous MEG activity have been performed to characterize abnormal brain activity in several neurological and psychiatric disorders. Focal slow wave MEG activity (2–6 Hz) was found to be associated with impaired neuronal function. Recently, we investigated spontaneous MEG activity in patients with depression and found an enrichment of slow wave activity over the left DLPFC (Maihofner et al., 2005). This agrees with PET studies demonstrating hypometabolism in this cortex in depressive patients. Furthermore, abnormal slow wave activity has been found around brain tumor borders, brain infarctions or during transient global amnesia (Kamada et al., 1997, Kamada et al., 2001, Stippich et al., 2000). Therefore, slow MEG wave activity appears to be associated with decreased neuronal activity. Additionally, several studies found an abnormal increase of focal spontaneous beta wave activity (12.5–30 Hz) in the areas of or adjacent to brain lesions (Vieth et al., 1996). There is also evidence for an interhemispheric phase synchrony and amplitude correlation of spontaneous beta oscillations in human subjects (Nikouline et al., 2001). This was interpreted as spontaneous brain activity associated with the resting state. Finally, in a recent study, we were able to detect increased fast MEG activity in the auditory cortex during auditory hallucinations in schizophrenia (Ropohl et al., 2004). This pattern of activation was similar to increases of fMRI signals during auditory hallucinations (Dierks et al., 1999). Therefore, in the present study, we extended these previous findings and hypothesized that patients with OCD may have alterations of their spontaneous MEG activity pattern. We investigated both slow (2–6 Hz) and fast (12.5–30 Hz) spontaneous magnetoencephalographic (MEG) activity in ten patients with OCD compared to ten healthy control subjects.
Section snippets
Results
Patients showed a significant increase of spontaneous MEG activity in the fast frequency range (12.5–30 Hz) over the left hemisphere for both Dtotal and Dmax (Dtotal: 3100 ± 334 versus 2061 ± 222; p < 0.05; Dmax: 78 ± 11 versus 29 ± 10; p < 0.05; Figs. 1A/B). This activity was concentrated over the left superior temporal gyrus (Fig. 2), while no focal dipole concentration was found for fast MEG activity of the left hemisphere in controls. Values of Dtotal and Dmax of patients were not correlated with
Discussion
In the present study, we compared spontaneous MEG recordings of OCD patients with those of a healthy age- and sex-matched control group. Our results provide evidence for an increase of fast MEG activity over the left hemisphere in the OCD group. Magnetic source imaging located this increase to activity in the left superior temporal gyrus. Furthermore, we found an enrichment of slow MEG activity over the left DLPFC in OCD patients, a finding which was absent in controls.
Converging evidence in
Patients and controls
Informed written consent was obtained from all subjects, and the study was approved by the local ethics committee. We included ten right-handed patients diagnosed with OCD (six males, four females; mean age = 32.5 ± 6.3 years, disease duration 5–17 years). OCD was diagnosed by a psychiatric consultant (WS) according to the criteria of the DSM-IV classification system. Scores on the Yale–Brown Obsessive-compulsive scale (Goodman et al., 1989) were recorded 2 days before MEG measurements (baseline)
Acknowledgment
We gratefully thank Tassilo Mathiowetz for his technical support.
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Contributed equally to this work.