Overall, the vSTR model was highly significant [ Figure 2 ; F (8,17) = 10.39; P < 0.001; adjusted R 2 adjusted = 0.75], such that age [ β = −0.29 t (17) = −2.30; P < 0.05], intertemporal preference [log(k): β = −0.31 t (17) = 2.14; P < 0.05], reward sensitivity [ β = 0.51 t (17) = 4.35; P < 0.001], right vSTR–vmPFC connectivity [ β = 0.58 t (17) = 3.96; P < 0.001] and right vSTR–dlPFC connectivity [ β = −0.33 t (17) = −2.15; P < 0.05] were all associated with MTE.
An association between smartphone usage and DD was, however, also signaled by a significant relationship between ASU and the mean indifference point for long delays ( r = 0.29; P = 0.031) and by a correlation between ASU and discounting rate that fell just short of statistical significance ( r = 0.260; P = 0.053).
The simple bivariate relationship among the behavioral variables in this small neuroimaging sample, summarized in Table 4 ( Supplementary Table S2 provides the complete correlation table for all measures in Study 2), was generally consistent with the pattern of findings from the larger cohort in Study 1, though some of the correlations failed to reach significance in this smaller sample.