Abstract
BackgroundDepression is one of the most prevalent mood disorders, and is known to be associated with abnormal functional connectivity in neural networks of the brain. Interestingly, a significant proportion of patients with depression experience spontaneous remission without any treatment. However, the relationship between electroencephalographic (EEG) functional connectivity and the spontaneous remission in depression remains poorly understood. Here, we investigated regional and network brain activity using EEG signals from a chronic restraint stress (CRS)-induced mouse model of depression. After 1 (CRS1W) or 3 weeks (CRS3W) following the cessation of a 4-week-long CRS, mice were subjected to depression-associated behavioral tasks. EEG signals were obtained from eight cortical regions (frontal, somatosensory, parietal, and visual cortices in each hemisphere).ResultsThe CRS1W group exhibited behavioral dysfunctions in the open field and forced swim tasks, whereas the CRS3W group displayed normal levels of behaviors in those tasks. In a linear correlation analysis, the CRS1W group exhibited increased correlation coefficient values at all frequency bands (delta, 1.5–4; theta, 4–8; alpha, 8–12; beta, 12–30; gamma, 30–80 Hz) compared with the control group. However, the differences in delta- and gamma-frequency bands between the control and CRS1W groups were no longer observed in the CRS3W group. Persistent brain network homology revealed significantly different functional connectivity between the control and CRS1W groups, and it demonstrated a huge restoration of the decreased distances in the gamma-frequency band for the CRS3W group. Moreover, the CRS3W group displayed a similar strength of connectivity among somatosensory and frontal cortices as the control group.ConclusionA mouse model of CRS-induced depression showed spontaneous behavioral remission of depressive behavior. Using persistent brain network homology analysis of EEG signals from eight cortical regions, we found that restoration of gamma activity at the network level is associated with behavioral remission.Electronic supplementary materialThe online version of this article (doi:10.1186/s12868-016-0239-x) contains supplementary material, which is available to authorized users.
Highlights
Depression is one of the most prevalent mood disorders, and is known to be associated with abnormal functional connectivity in neural networks of the brain
The forced swimming test (FST) for despair-like behavior and the open-field test for locomotor activity and anxiety were conducted at 1 week (CRS1W group) and 3 weeks (CRS3W group) following cessation of 4-week chronic restraint stress (CRS) (Fig. 1a)
In the FST, immobility in the CRS1 W group increased compared to the control group (191.76 ± 6.27 vs. 155.82 ± 6.20 s; p < 0.05 by Mann–Whitney U-test, Fig. 1b), whereas the immobile time in the CRS3W group (144.40 ± 10.83 s) was consistent with the control group
Summary
Depression is one of the most prevalent mood disorders, and is known to be associated with abnormal functional connectivity in neural networks of the brain. Depression is a common mental disorder that affects approximately 121 million people worldwide, and is considered one of the leading causes of disability. This disorder is associated with increased physical illness, decreased social functioning, and a high mortality rate, resulting in huge social and economic strain [1]. There have been no EEG studies concerning functional connectivity at the network level in the brain during spontaneous remission from depression
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