Deficient inhibition underlies salience network hyperactivity in stress and anxiety

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ABSTRACT Decades of research notwithstanding, there remains an urgent need to uncover the neurobiology of stress and anxiety and develop effective biomarkers for these conditions. The salience network (SN), a major intrinsic neural network anchored in the frontal lobe, consistently exhibits hyperactive functioning in stress and anxiety. This SN hyperactivity has been recognized as a novel brain network pathology, but its underlying mechanism remains elusive. EEG alpha (8-12 Hz) oscillations, dominating intrinsic neural rhythmic activity, play a critical role in cortical inhibition. Particularly, prevalent posterior-to-frontal (P→F) alpha projection (i.e., alpha directional connectivity) transmits alpha inhibitory influence from the occipitoparietal cortex (a primary alpha source) to the frontal lobe. By driving bottom-up cortical inhibition and gating sensory propagation that triggers the SN, alpha P→F connectivity can serve to downregulate the SN. Prominently featured in “thalamocortical dysrhythmia” or “oscillopathy” models of neuropsychiatric disorders, alpha dysrhythmia (particularly, deficient alpha P→F connectivity) has been increasingly observed in stress and anxiety, motivating our hypothesis that deficient alpha P→F connectivity underlies SN hyperactivity in stress and anxiety. Leveraging an integrative methodology of simultaneous EEG-fMRI combined with experimental anxiety induction via stress exposure, this project (N = 140) will establish a mechanistic role of alpha P→F hypoconnectivity in the genesis and maintenance of SN hyperactivity in stress and anxiety. This discovery will further identify an accessible, low-cost EEG biomarker for SN hyperactivity and for stress and anxiety in general. Finally, this discovery will isolate a new treatment target that is highly responsive to non-invasive brain stimulation (NIBS), motivating an R01 to normalize alpha P→F connectivity as a novel intervention for stress and anxiety.