Abstract
The hippocampus is a core brain region that responds to stress. Previous studies have found a dysconnectivity between hippocampus and other brain regions under acute and chronic stress. However, whether and how acute social stress influences the directed connectivity patterns from and to the hippocampus remains unclear. In this study, using a within-subject design and Granger causal analysis (GCA), we investigated the alterations of resting state effective connectivity from and to hippocampal subregions after an acute social stressor (the Trier Social Stress Test). Participants were engaged in stress and control conditions spaced approximately one month apart. Our findings showed that stress altered the information flows in the thalamus-hippocampus-insula/midbrain circuit. The changes in this circuit could also predict with high accuracy the stress and control conditions at the subject level. These hippocampus-related brain networks have been documented to be involved in emotional information processing and storage, as well as habitual responses. We speculate that alterations of the effective connectivity between these brain regions may be associated with the registering and encoding of threatening stimuli under stress. Our investigation of hippocampal functional connectivity at a subregional level may help elucidate the functional neurobiology of stress-related psychiatric disorders.
Highlights
Stress is a ubiquitous feature of fast-changing societies, and empirical studies have shown that stress can have a profound impact on various facets of emotional and cognitive functions (Sandi, 2013; Vogel et al, 2016)
Being consistent with previous studies (Dickerson and Kemeny, 2004; Ginis et al, 2012), which suggest that the cortisol reactivity reaches its peak between 21 and 40 min following stressor onset, post-hoc t tests showed that the stress condition induced higher cortisol than the control condition at T3 (t(26) = 2.677, p = 0.013), T4 (t(26) = 4.503, p < 0.001), T5
Post-hoc t tests showed significantly higher negative emotion ratings in the stress condition than in the control condition at T2 (t(29) = 4.413, p < 0.001) and T3 (t(29) = 4.763, p < 0.001). These findings suggest that acute stress increased cortisol level and modulated emotional experience
Summary
Stress is a ubiquitous feature of fast-changing societies, and empirical studies have shown that stress can have a profound impact on various facets of emotional and cognitive functions (Sandi, 2013; Vogel et al, 2016). Previous studies have found stress-induced structural and functional alterations in the hippocampus and its subregions, whether and how stress influences the effective connectivity patterns involving the hippocampal subfields remains unclear. We conducted a whole-brain analysis to explore the stress-induced effective connectivity alteration of hippocampal subregions with brain areas restricted to the limbic system, including the bilateral amygdala, anterior cingulate cortex, midbrain, insula and thalamus These brain structures are structurally and functionally connected with the hippocampus, and constitute a neural network associated with the processing and modulation of emotions, and are all documented to be vulnerable to acute and chronic stress SVM is popular for its high flexibility and accuracy as well as its capability to deal with numerous features with few training patterns (Guyon et al, 2002; Liu et al, 2017; Lou et al, 2017)
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