**Figure 2.** **Mediation analysis.** (**A**) Represents mediation model 1: subjective cognitive complaints as the dependent variable (Y), the average MD as the independent variable (X), and the average cortical thickness as the mediator (M); (**B**) Represents mediation model 2: subjective cognitive complaints as the dependent variable (Y), the average MD as the independent variable (X), and the TIV-corrected hippocampal volume (left+right) as the mediator (M). (**C**) Represents mediation model 3: subjective cognitive complaints as the dependent variable (Y), cortical thickness as the independent variable (X), and the average MD as the mediator (M); (**D**) Represents mediation model 4: subjective cognitive complaints as the dependent variable (Y), the TIV-corrected hippocampal volume (left+right) as the independent variable (X), and the average MD as the mediator (M). Note: age was not a significant covariate in models 1 and 3. SCC: subjective cognitive complaints; ACME: average causal mediation effect; ADE: average direct effect; M: mediator; Magnitude of the mediation effect: ACME / total effect; X: independent variable; Y: dependent variable. *p<0.05; **p<0.01; ***p<0.001.