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Fronto-striatal connectivity predicts patience
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Age effects on the frontostriatal tract
Cross-sectional data at T1 and T2 showed that white matter integrity of the fronto-striatal tract increased with age. Age was significantly positively correlated with FA at T1 (r=.440, p<.001) and at T2 (r=.351, p<.001), and significantly negatively correlated with MD at T1 (r=-.220, p=.002), but not at T2 (r=-.089, p=.089). Moreover, white
matter integrity measures were positively correlated between T1 and T2 (FA: r=.611, p<.001; MD: r=.583, p<.001).
Longitudinal analyses revealed that age-related change in white matter integrity (FA and MD) was best explained by a cubic age-model (FA: age1: β=0.152, p<.001; age2: β=-0.050, p=.006; age3: β=0.047, p=.004; MD: age1: β=-0.00010, p<.001; age2: β=0.00005, p=.018; age3: β=-0.00007, p=.001) see Table 2. More specifically, our data indicate that FA mostly increased during childhood and early adulthood. The reversed pattern of FA-changes was observed for MD (see Figure 2b and 2c). Analyses only including 8-18 year old participants revealed that age-related change in white matter integrity was best explained by a quadratic age-model (FA: age1: β=0.137, p<.001; age2: β=-0.048, p=.005; age3: β=0.022, p=.1220; MD: age1: β=-0.00011, p<.001; age2: β=0.00005, p=.015; age3: β=-0.00003, p=.131). Additional analyses showed that there were no significant gender or gender x age interaction effects in white matter integrity (nor in FA or in MD).
Mediation analyses
To investigate the relation between age and white matter integrity in explaining variance in delay of gratification skills, we performed mediation analyses using the Preacher and Hayes method (Preacher and Hayes, 2008). At T1, the effect of age on delay of gratification (path c: B=.016, p=.004) was fully mediated by FA (path a: B=.123, p<.001; path b: B= .067, p= .0019; path c’: B=.008, p=.195; mediation effect a*b: 95% confidence interval (CI) .0034 - .0140; p=.004), see Figure 3a. Furthermore, the effect of age on delay of gratification skills (path c: B=.016, p=.004) was significantly mediated by MD (path a: B=-.0614, p=.002; path b: B=-.059, p=.003; Path c’: B=.012, p=.026; mediation effect a*b: 95% CI .0012 - .0076; p=.030).
Partly overlapping results were found at T2: FA was a significant mediator of the association between age and delay of gratification skills (path c: B=.014, p=.005; path a: B=.097, p<.001 ; path b: B=.038, p=.047; Path c’: B=.011, p=.046; mediation effect a*b: 95% CI .0004 - .0081; p=.061), see Figure 3b. However, MD within the fronto-striatal-tract did not mediate the association between age and delay of gratification skills (path c: B=.014, p=.005; path a: B=- .035, p= .083; path b: B=.012, p=0.488; path c’: B=.015, p=.004; mediation effect a*b: 95% CI= -.0028 - .0006; p=.517). Thus, the relation between age and delay of
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