Global field synchronization (GFS)
quantifies the synchronization level of brain oscillations. The GFS method has
been introduced to measure functional synchronization of EEG data in the
frequency domain. GFS also detects phase interactions between EEG signals
acquired from all of the electrodes. If a considerable amount of local brain
neurons has the same phase, these neurons appear to interact with each other.
EEG data were received from 17 obsessive-compulsive disorder (OCD) patients and
17 healthy controls (HC). OCD effects on local and large-scale brain circuits
were studied. Analysis of the GFS results showed significantly decreased values
in the delta and full frequency bands. This research suggests that OCD causes
synchronization disconnection in both the frontal and large-scale regions. This
may be related to motivational, emotional and cognitive dysfunctions.
Discussion: Our results are similar to previous results that indicate decreased GFS in neuroleptic-naive patients with schizophrenia [24,25,26, 47]. Moreover, our recent findings are also consistent with earlier EEG synchronization works, including different signal processing methods used to understand the mechanism of OCD [34, 53]. We have focused on synchronization analysis of EEG frequency band activities because the literature indicates that synchronous brain oscillations in slow frequency bands provide important information about both motivational and cognitive processes (memory, attention, perception, decision-making and planning) [1, 39, 50] Neuroimaging studies analyse both PET and fMRI slices for estimation of brain dynamics and detection of the location generated delta band activity. In these studies, it was reported that the subcortical centres generating delta band activity are in both the medial prefrontal cortex and the orbitofrontal cortex [2, 17, 21,22,23, 35, 43] EEG methods such as synchronization, complexity analysis, etc. are used only for exclusion of the comorbid disease (for instance depression with OCD) with obsessive-compulsive symptoms in clinical practise. In treatment or therapeutic use of EEG methods is very limited. This study was shown that global field synchronization analysis (GFS) values may be used as biomarker for OCD, and it can be used also for monitoring course of disease and treatment. GFS studies are shown that synchronization power is important marker for diagnosis of neuropsychiatric diseases.
In future work, we plan to compare the performance of those global synchronization metrics as follows: OC, GFS, GSI and GCI in detecting the severity of OCD. In addition, we will investigate the relationship between interneuronal synchronization and the degree of EEG complexity within a short time interval.
Conclusion: Some of the investigations on OCD effects on the brain sites have shown important patterns. Neuropsychological tests indicated that OCD causes functional dysfunctions on frontal lobe , neuroimaging studies also support these findings . One of our results is decreased synchronization on frontal site is consistent with this study.
EEG synchronization level of OCD patients was investigated, and the level was found low for delta and full frequency range. Loss of phase synchronization would have relevance with functional connectivity. The major findings of the present study are that the loss of synchronization in delta band and functional connectivity of the brain changes with OCD. Studies using low resolution brain electromagnetic tomography (LORETA) have founded delta activity at maximum level in medial prefrontal cortex and orbito-frontal cortex . In addition to this, investigations with fMRI have detected abnormal and dysfunctional activity in orbito-fronto striatal networks of OCD patients  and fronto-subcortical network dysfunctional causes a loss of functional connectivity in the brain [2, 15, 35, 37]. Our results that functional connectivity and desynchronization in delta band for frontal and global site are also consistent with previous findings.