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Introduction: Mental disorders are a significant concern in contemporary society, with a pressing need to identify biological markers. Long-range temporal correlations (LRTC) of brain rhythms have been widespread in clinical cohort studies, especially in major depressive disorder (MDD). However, research on LRTC in obsessive-compulsive disorder (OCD) is severely limited. Given the high co-occurrence of OCD and MDD, we conducted a comparative LRTC investigation. We assumed that the LRTC patterns will allow us to compare measures of brain cortical balance of excitation and inhibition in OCD and MDD, which will be useful in the area of differential diagnosis. Methods: In this study, we used the 64-channel resting state EEG of 29 MDD participants, 26 OCD participants, and a control group of 37 volunteers. Detrended fluctuation analyzes was used to assess LRTC. Results: Our results indicate that all scaling exponents of the three subject groups exhibited persistent LRTC of EEG oscillations. There was a tendency for LRTC to be higher in disorders than in controls, but statistically significant differences were found between the OCD and control groups in the entire frontal and left parietal occipital areas, and between the MDD and OCD groups in the middle and right frontal areas. Discussion: We believe that these results indicate abnormalities in the inhibitory and excitatory neurotransmitter systems, predominantly affecting areas related to executive functions. [ABSTRACT FROM AUTHOR]

Concurrent EEG and fMRI acquisitions in resting state showed a correlation between EEG power in various bands and spontaneous BOLD fluctuations. However, there is a lack of data on how changes in the complexity of brain dynamics derived fromEEG reflect variations in the BOLD signal. The purpose of our study was to correlate both spectral patterns, as linear features of EEG rhythms, and nonlinear EEG dynamic complexity with neuronal activity obtained by fMRI. We examined the relationships between EEG patterns and brain activation obtained by simultaneous EEG-fMRI during the resting state condition in 25 healthy right-handed adult volunteers. Using EEG-derived regressors, we demonstrated a substantial correlation of BOLD signal changes with linear and nonlinear features of EEG. We found the most significant positive correlation of fMRI signal with delta spectral power. Beta and alpha spectral features had no reliable effect on BOLD fluctuation. However, dynamic changes of alpha peak frequency exhibited a significant association with BOLD signal increase in right-hemisphere areas. Additionally, EEG dynamic complexity as measured by the HFD of the 2-20Hz EEG frequency range significantly correlated with the activation of cortical and subcortical limbic system areas. Our results indicate that both spectral features of EEG frequency bands and nonlinear dynamic properties of spontaneous EEG are strongly associated with fluctuations of the BOLD signal during the resting state condition. [ABSTRACT FROM AUTHOR]

Objectives Concurrent EEG and fMRI acquisitions in resting state showed a correlation between EEG power in various bands and spontaneous BOLD fluctuations. However, there is a lack of data how the EEG complexity of brain dynamic, such as instability or entropy of EEG rhythmic structure, may reflect variations in the BOLD signal. Methods We aimed to find the relationships between EEG dynamics and brain activation obtained by simultaneous EEG-fMRI during resting state condition in 25 healthy right-handed adult voluntaries. We applied nonlinear analysis in order to obtain chaotic features of EEG, which we used as regressors in GLM relating to changes in the BOLD signal. Results Fluctuations in beta rhythm were associated with the BOLD signal increase in basal ganglia and thalamic structures ( p < 0.05 , FDR-corrected). Moreover, our data showed that Higuchi fractal dimension correlated with activation of cortical areas and limbic system regions. Offset of alpha-peak frequency and envelope frequency coincided with activation of thalamus, insula, hippocampus and temporal cortex predominantly in the right hemisphere. Conclusions Previously, nonlinear EEG analysis in clinical neurophysiology pointed that decreased complexity of brain dynamics might implicate increased neuronal interaction. Our results indicate that dynamic properties of spontaneous EEG have a significant association with resting state BOLD fluctuations reflecting possible sources of rhythmic neuronal activity. In particular, the observed increase in the BOLD signal significantly correlated with deviation of beta rhythm power that supports the hypothesis of basal-thalamic origin of beta rhythm. The study was supported by a grant of the Russian Science Foundation 116-15-00300. [ABSTRACT FROM AUTHOR]

• A cluster of 67 functional connections distinguished the OCD, MDD and control groups. • Three functional connections were stronger in the OCD than in the MDD group. • DMN connectivity strength was higher in the control group than in the MDD and OCD groups in the alpha and beta bands. Major depressive disorder (MDD) and obsessive-compulsive disorder (OCD) are psychiatric disorders that often co-occur. We aimed to investigate whether their high comorbidity could be traced not only by clinical manifestations, but also at the level of functional brain activity. In this paper, we examined the differences in functional connectivity (FC) at the whole-brain level and within the default mode network (DMN). Resting-state EEG was obtained from 43 controls, 26 OCD patients, and 34 MDD patients. FC was analyzed between 68 cortical sources, and between-group differences in the 4–30 Hz range were assessed via the Network Based Statistic method. The strength of DMN intra-connectivity was compared between groups in the theta, alpha and beta frequency bands. A cluster of 67 connections distinguished the OCD, MDD and control groups. The majority of the connections, 8 of which correlated with depressive symptom severity, were found to be weaker in the clinical groups. Only 3 connections differed between the clinical groups, and one of them correlated with OCD severity. The DMN strength was reduced in the clinical groups in the alpha and beta bands. It can be concluded that the high comorbidity of OCD and MDD can be traced at the level of FC. [Display omitted] [ABSTRACT FROM AUTHOR]

Altered functional connectivity of the amygdala has been observed in a resting state immediately after fear learning, even one day after aversive exposure. The persistence of increased resting-state functional connectivity (rsFC) of the amygdala has been a critical finding in patients with stress and anxiety disorders. However, longitudinal changes in amygdala rsFC have rarely been explored in healthy participants. To address this issue, we studied the rsFC of the amygdala in two groups of healthy volunteers. The control group participated in three fMRI scanning sessions of their resting state at the first visit, one day, and one week later. The experimental group participated in three fMRI sessions on the first day: a resting state before fear conditioning, a fear extinction session, and a resting state immediately after fear extinction. Furthermore, this group experienced scanning after one day and week. The fear-conditioning paradigm consisted of visual stimuli with a distinct rate of partial reinforcement by electric shock. During the extinction, we presented the same stimuli in another sequence without aversive pairing. In the control group, rsFC maps were statistically similar between sessions for the left and right amygdala. However, in the experimental group, the increased rsFC mainly of the left amygdala was observed after extinction, one day, and one week. The between-group comparison also demonstrated an increase in the left amygdala rsFC in the experimental group. Our results indicate that functional connections of the left amygdala influenced by fear learning may persist for several hours and days in the human brain. • Resting-state amygdala functional connectivity changes after fear extinction. • Altered amygdala connectivity persisted in one week after fear extinction. • The left amygdala exhibited more prominent changes in functional connectivity. [ABSTRACT FROM AUTHOR]