Higher Morning Cortisol in Childhood Predicts Larger Right Amygdala Volume in Adolescence

• Milan Mathew, Biomedical Engineering, University of Delaware

• Mary Dozier, Psychological and Brain Sciences, University of Delaware

The transition from childhood into adolescence is a critical time of neurodevelopmental reorganization, during which subcortical structures undergo significant change, yet the biological factors that shape this trajectory remain poorly understood. Morning waking cortisol serves as a primary biological indicator of daily stress regulation, reflecting baseline endocrine activity and physiological readiness upon waking. Simultaneously, the right amygdala acts as a key physiological alarm system involved in rapid threat processing and emotional reactivity, rich in stress hormone receptors. While cross-sectional research links stress chemistry to brain structural variations, longitudinal evidence explaining how childhood cortisol output shapes subsequent brain development remains limited. This study investigated whether baseline morning cortisol output in middle childhood (Age 9) prospectively predicts right amygdala volume four years later in early adolescence (Age 13). A total of 92 youth participants were pulled from a larger, longitudinal study. Morning cortisol, the primary predictor, was determined using salivary samples collected across multiple days upon waking at age 9. Right amygdala volume at age 13, the outcome variable, was determined using T1-weighted structural MRI scans and FreeSurfer automated segmentation. Multiple linear regression revealed that after controlling for sex, risk status, and overall brain volume, higher average morning cortisol at age 9 significantly predicted larger right amygdala volume at age 13 (p = .04, β = .84). These findings suggest that stress hormones in childhood may have a role in shaping subcortical brain development across the transition into adolescence, which may alter long-term vulnerability to internalizing symptoms.