Date of Graduation

5-2026

Document Type

Thesis

Degree Name

Bachelor of Science in Biology

Degree Level

Undergraduate

Department

Biological Sciences

Advisor/Mentor

Leong, Josiah

Committee Member

Paul, Kathleen

Second Committee Member

Becker, Brian

Third Committee Member

Paré, Adam

Abstract

Medical practitioners are diagnosing Attention-Deficit/Hyperactivity Disorder (ADHD) at a high and ever-increasing rate. The use of stimulant medication to treat ADHD is also increasing and is associated with changes in the brain. Past research found that children with ADHD have lower volume in reward neurocircuitry, such as the ventral tegmental area (VTA) and the nucleus accumbens (NAcc). Research has also found that stimulant usage in those with ADHD might “normalize” the reward circuits. However, few longitudinal studies have directly tested the long-term effects of stimulant medication on brain development. Here we tested whether long-term stimulant use is associated with changes to the VTA-NAcc structural white-matter tract. We analyzed longitudinal data from the Adolescent Brain Cognitive Development (ABCD) study and created 4 groups: adolescents with no ADHD symptoms and no stimulant use, adolescents with ADHD symptoms and no stimulant use, adolescents who discontinued stimulants after baseline, and adolescents on stimulants for at least 3 years past baseline. We predicted greater structural connectivity in the VTA-NAcc tract in adolescents with continuous stimulant use compared to those who discontinued stimulants and those with ADHD symptoms not taking stimulants. Results showed that adolescents who discontinued stimulants after baseline displayed significantly lower structural connectivity in the VTA-NAcc tract than those with no ADHD symptoms and no stimulant use as well as those with ADHD symptoms and no stimulant use. Adolescents with long-term stimulant use displayed no significant difference in structural connectivity from those with no ADHD symptoms and no stimulant use. These findings suggest that reduced integrity in the VTA–NAcc tract may be associated with more severe ADHD-related presentations, while long-term stimulant use may be linked to normalizing the tract.

Keywords

ADHD; Stimulant Medication; White Matter Integrity; Mesolimbic Pathway; dMRI; Adolescents

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