As we noted earlier, our indicators of structural and functional integrity of the DMN are correlated, so we investigated whether any (albeit small) link between structural degradation and memory may be mediated by functional connectivity. A formal mediation analysis revealed this to be the case in that the unstandardized regression coefficient (i.e., B) between structural integrity (as measured by GMV-VM/VSM-PLS) and episodic memory (VM, B = 8.36; VSM, B = 3.28) dropped significantly when functional connectivity (as measured by FC-VM/VSM-PLC) was taken into account (VM, B = 3.06, Aroian test p < 0.001; VSM, B = 1.41, Aroian test p = 0.029). To highlight this directional influence, examining structural integrity as the mediator did not reveal significant results (VM, Aroian test p = 0.07; VSM, B = 1.41, Aroian test p = 0.21). Together, these findings support the idea that structural integrity shapes the possible dynamics of neuronal activity and that changing patterns of these dynamics underlie behavioural variability.
