Abstract
Loneliness, a subjective state of perceived social isolation characterized by chronic social hypervigilance, is a profound risk factor for physical and mental health conditions. While functional neuroimaging studies link loneliness to altered salience network connectivity, the sub-second temporal dynamics of the resting lonely brain remain unexplored. We investigated the relationship between trait loneliness and resting-state electroencephalography (EEG) microstates. Sixty-one healthy young adults completed the UCLA Loneliness Scale and Beck Depression Inventory-II (BDI-II) and underwent 3-minute resting-state EEG recording. A criterion-based five-class microstate solution identified a topography corresponding to the canonical Class C/E, associated with both self-referential and salience-related processing. Higher loneliness scores were significantly associated with reduced Class C/E occurrence, which remained significant after controlling for depressive symptoms, age, and sex. Exploratory source localization revealed that lonelier individuals showed reduced current density in the middle cingulate cortex (MCC). These findings suggest that chronic social hypervigilance suppresses the spontaneous mobilization of the salience network at rest, with reduced MCC engagement reflecting a dispositional attenuation consistent with chronic relational threat.