Impact of circadian rhythm disruptions on the emotional brain: gray matter and functional connectivity changes in the amygdala

Acute circadian rhythm disruption (ACRD), increasingly prevalent in modern society due to chronic sleep disturbance and irregular sleep-wake patterns, has been linked to emotional dysregulation, including heightened susceptibility to depression and anxiety. Although the amygdala plays a critical role in emotional processing, the direct effects of ACRD on its morphology and function—and how these changes relate to sleep and affective disturbances—remain unclear. In this longitudinal study, healthy participants underwent 15 days of experimentally induced circadian rhythm disruption, which led to sleep and emotional disturbances. Questionnaire-based symptoms of the rhythm disorder restored by the 30-day follow-up. Ultra-high field (7 T) MRI scans were acquired before and after the intervention to assess morphology and functional changes in amygdala gray matter volume (GMV) and functional connectivity (FC). Our findings revealed a significant reduction in GMV within the left amygdala and its subregions—including the centromedial (CM), laterobasal (LB), and superficial (SF) nuclei — following ACRD. In contrast, no significant GMV changes were detected in the right amygdala or its corresponding subregions, suggesting a lateralized effect of ACRD. Moreover, GMV reductions in the left amygdala were significantly correlated with worsening scores on the Pittsburgh Sleep Quality Index (PSQI). Functional connectivity analysis demonstrated a nearly significant decrease in connectivity between the left medial prefrontal cortex (mPFC) and the left CM amygdala. Crucially, this work is the first to systematically investigate the neurobiological effects of ACRD on amygdala integrity and its implications for emotional regulation.