Table 4 Age moderation of brain-behavior relationships: Tract density × age interaction effects validated by permutation testing

Cognitive test	Network	Interaction β	SE	p (Parametric)	p (Permutation)	q (FDR)	Younger r	Middle r	Older r	Δr
TMT-A (seconds)	SalVentAttn	−0.126	0.023	<0.001	<0.001	<0.001	0.044	0.019	−0.276	−0.320
TMT-A (seconds)	Cont	−0.097	0.021	<0.001	<0.001	<0.001	−0.054	−0.013	−0.234	−0.180
TMT-A (seconds)	DorsAttn	−0.070	0.018	<0.001	0.003	0.006	−0.119	−0.091	−0.222	−0.103
TMT-A (seconds)	Default	−0.069	0.013	<0.001	<0.001	<0.001	0.089	−0.041	−0.224	−0.313
TMT-A (seconds)	SomMot	−0.051	0.010	<0.001	<0.001	<0.001	−0.017	0.033	−0.239	−0.223
TMT-B (seconds)	SalVentAttn	−0.191	0.074	0.010	0.010	0.019	0.070	0.020	−0.121	−0.191
TMT-B (seconds)	Cont	−0.144	0.069	0.037	0.056	0.065	0.065	−0.051	−0.081	−0.146
TMT-B (seconds)	DorsAttn	−0.113	0.060	0.060	0.062	0.066	0.028	−0.060	−0.083	−0.111
TMT-B (seconds)	SomMot	−0.100	0.034	0.003	<0.001	<0.001	0.131	0.019	−0.107	−0.238
TMT-B (seconds)	Default	−0.092	0.043	0.031	0.054	0.065	0.105	−0.161	−0.078	−0.183
RAVLT (total recall)	Cont	0.049	0.023	0.031	0.015	0.025	−0.022	0.131	0.235	0.257
RAVLT (total recall)	SalVentAttn	0.048	0.025	0.050	0.021	0.030	0.007	0.099	0.221	0.214
RAVLT (total recall)	SomMot	0.032	0.011	0.004	0.001	0.003	−0.103	0.062	0.234	0.338
RAVLT (total recall)	DorsAttn	0.032	0.020	0.117	0.070	0.070	−0.064	0.072	0.152	0.215
RAVLT (total recall)	Default	0.031	0.014	0.030	0.022	0.030	−0.017	0.142	0.183	0.200

Interaction coefficients represent the Tract Density × Age term from linear regression models including sex as covariate. All effects validated by permutation testing (1000 iterations). FDR correction (Benjamini–Hochberg) applied across 15 tests. Age groups based on tertiles: Younger (36.0–51.75 years, N = 239), Middle (51.75–67.83 years, N = 238), Older (67.92–100.0 years, N = 241). Correlation values (r) calculated separately within each age group using Pearson correlation. Δr = change in correlation from Younger to Older group. Negative interactions for TMT indicate that the protective effect of higher tract density (shorter completion times) becomes stronger with age. Positive interactions for RAVLT indicate that the beneficial effect of higher tract density on memory becomes stronger with age. Results sorted by cognitive test and interaction effect size.
SomMot Somatomotor, DorsAttn Dorsal Attention, SalVentAttn Salience/Ventral Attention, Cont Control, RAVLT Rey Auditory Verbal Learning Test, TMT Trail Making Test, FDR False Discovery Rate.

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