Date of Graduation

5-2026

Document Type

Thesis

Degree Name

Bachelor of Science in Biology

Degree Level

Undergraduate

Department

Psychological Science

Advisor/Mentor

Josiah Leong

Committee Member

Josiah Leong

Second Committee Member

Matt Judah

Third Committee Member

Yuchun Du

Fourth Committee Member

Faith Lessner

Abstract

Adolescence is a period of transition from childhood to adulthood when people explore risky behaviors, and stressors during adolescence can change structural brain connectivity. Previous research has found weaker structural connectivity between reward circuits and future cognitive impairments among children raised in orphanages. Comparative research in mice suggests that social isolation after bullying can damage these connections and induce alcohol seeking. We tested whether social isolation was related to lower connectivity of targeted structural connections and anxious behaviors in adolescent humans. We analyzed data from the Adolescent Brain Cognitive Development study and found 522 subjects had experienced extreme social isolation. To evaluate the level of social isolation experienced by each subject, we averaged their scaled answers to questions regarding isolation and investigated the subjects two standard deviations above the mean. We predicted that social isolation would alter connectivity between reward circuits, which may lead to future risk seeking. The tracts that we studied included the uncinate fasciculus and the connection between the amygdala and nucleus accumbens. We characterized the structural connectivity between reward circuits in our group of subjects from MRI scans to evaluate our tracts of interest. We found that in socially isolated adolescents, there was impaired connectivity in the left uncinate fasciculus (p = .024) and abnormally stronger connectivity between the left amygdala and nucleus accumbens (p = .015). We also found that social isolation was correlated strongly with anxiety symptoms (p < .001) and alcohol use (p < .001). These findings suggest that social isolation during adolescence is linked to altered connectivity in reward circuit white matter and increased vulnerability to anxiety and risk‑seeking behaviors.

Keywords

Adolescence; neuroscience; social isolation; substance use; reward circuitry, anxiety

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