Table 9.
Topological association between CT and SW density and related mediation analysis
| Total effect of age at each derivation (path c) (b, p-value) | CT cluster (BAs, peak) | Lat | Cluster size (corrected p value) | Conjunct vertices (age and SW) | Parameter estimates (simple mediation models) |
|||
|---|---|---|---|---|---|---|---|---|
| Path a | Path b | Path c′ | Indirect effect (b, 95% CI, K2) | |||||
| Prefrontal b = −0.25, (p = 0.002) | IFP (BA40/BA43) (56 −18 20) | R | 85 vertices p = 0.05 | 85 | b = −0.20, p < 0.001 | b = 0.74, p < 0.001 | b = −0.10, p = 0.14 | b = −0.15 (−0.25 −0.06) (*) K2 = 0.26 |
| Central b = −0.36, (p < 0.001) | Insula (BA13/BA22) (46 −1 −10) | R | 171 vertices p = 0.002 | 171 | b = −0.30, p < 0.001 | b = 0.55, p < 0.001 | b = −0.20, p = 0.01 | b = −0.17 (−0.29 −0.07) (*) K2 = 0.25 |
| MFG (BA6) (30 −10 59) | R | 42 vertices p = 0.05 | 42 | b = −0.37, p < 0.001 | b = 0.68, p < 0.001 | b = −0.11, p = 0.18 | b = −0.25 (−0.43 −0.11) (*) K2 = 0.33 | |
| Parietal b = −0.42, (p < 0.001) | Insula (BA13) (46 −1 −10) | R | 119 vertices p = 0.007 | 119 | b = −0.30, p < 0.001 | b = 0.70, p < 0.001 | b = −0.21, p = 0.04 | b = −0.21 (−0.44 −0.08) (*) K2 = 0.25 |
| Middle cingulate (BA24) (2 −3 26) | R | 46 vertices p = 0.009 | 46 | NA | NA | NA | NA | |
Rows illustrate simple mediation models to explain age-related changes in SW density at other derivations (prefrontal, central, parietal, and occipital) with mean CT in each previously identified region as stand-alone mediators. Total effect of age on SW density is shown under each derivation. The cluster column depicts the relationship between cluster and SW density when controlling for age. The conjunction analysis column depicts the number of vertices also significantly associated with age-related thinning. Coefficients in each path necessary for the computation of indirect effects are shown in designated columns. b-values refer to unstandardized parameter estimates of paths shown in Figure 1. Indirect effects are significant at p < 0.05 when 0 is not included in the 95% CI and significance is denoted with an asterisk. K2 is an effect size of mediation and thus represents the proportion of the age-related effect on SW density that has been mediated by changes in CT (>0.25 = strong effect; >0.09 = medium effect; >0.001 = small effect). CT in each region is adjusted for ICV.