Figure 1.

Mediation model. We hypothesized that aging exerts its total effect on SW characteristics (path c) by an initial effect on CT (path a), which then drives changes in NREM sleep oscillations (path b). Mediation occurs when the relationship between aging and sleep oscillations drops significantly when entering the mediators as cofactors in the model (path a*path b = indirect effect). However, it is still possible for age to affect SW characteristics independently of CT through distinct mechanisms (path c′ = direct effect).