<p>This study empirically tests a theoretical model of ADHD that identifies aberrant frontal-to-subcortical projections—particularly those involving the ventral tegmental area and, consequently, the nucleus accumbens (NAc)—as a core neurobiological vulnerability. The model predicts reduced frontal influence on subcortical structures and group-by-direction interaction effects, especially at the NAc. Structural and resting-state fMRI data from sixty individuals with ADHD and sixty healthy controls were selected from the ADHD-200 dataset. The cortex was parcellated using MOSI (Modular Analysis and Similarity Measurements). The mean amplitude of low-frequency fluctuations (ALFF) and the mean time series were extracted for each frontal node. Subcortical nuclei—including the caudate, putamen, globus pallidus, NAc, and thalamus—were included in the analyses, with each voxel treated as a neural node. Correlation analyses were performed to examine the relationship between nodal power (ALFF) and nodal strength. Directional metrics were defined as frontal-to-subcortical (F2S) and subcortical-to-frontal (S2F) correlations between nodal strength and nodal power. Group differences and interactions were tested using t-tests and linear mixed-effects (LME) models. Correlation and LME analyses revealed a consistent bimodal pattern, with positive F2S and negative S2F associations across all subcortical nuclei, suggesting a directional excitation–inhibition balance. Reduced F2S slopes in ADHD and a significant group-by-direction interaction in the NAc (<i>p</i> = 0.009) supported model predictions. These findings are consistent with the proposed developmental model.</p>