The adolescent reward system: Longitudinal brain-behavior dynamics and pandemic effects.

Adolescence is a critical period of brain development characterized by heightened reward sensitivity, which influences behavior and emotional regulation. Major life events, like the COVID-19 pandemic, may affect reward system development. This longitudinal study integrates self-reported Behavioral Activation System (BAS) measures with fMRI data from the Adolescent Brain Cognitive Development Study® to examine reward processing during versus before the pandemic. 5,405 participants (Mage = 9.92, SD = 0.62) completed the Monetary Incentive Delay task during fMRI scanning and BAS assessments at Baseline and Year 2. Participants were grouped by whether their Year 2 follow-up occurred before or during the pandemic. Generalized linear mixed models examined changes in BAS subscales (Drive, Fun-Seeking, Reward Responsiveness); fMRI analyses assessed neural activation in key cortical/subcortical regions. Brain network analysis evaluated functional connectivity across reward and executive networks. Results revealed a decline across all BAS subscales at Year 2 compared to Baseline, with more pronounced reductions in BAS Drive among those assessed during the pandemic. Network analysis showed cohesive executive but variable reward network changes, especially in the right hemisphere. Developmental changes in reward sensitivity were accompanied by shifts in activation in core reward regions (e.g., nucleus accumbens, caudate, putamen, thalamus), which also varied by age and sex. Findings show declines in reward sensitivity over time, and reveal subtle but meaningful adaptations in reward-related brain function in relation to the pandemic, highlighting the need to consider individual differences during adolescence, especially under stress.