Fig. 1
From: Brain mediators of systemic oxidative stress on perceptual impairments in Parkinson’s disease
The diagram of the mediation hypothesis framework. In this mediation hypothesis framework, we want to identify the potential anatomical region which exhibited the mediation effect between oxidative stress level and perceptual function. We selected the oxidative stress as a predictor (X), perceptual functions as an outcome variable (Y), and regional gray matter with significant main disease effect (investigated from VBM analysis) as potential mediators (M). The three components of single level mediation analysis address the relationship between these variables. Indirect “path a” investigates the relationship between oxidative stress level and regional gray matter volume. Indirect “path b” investigates whether the regional gray matter volume predicts the perceptual functions after adjusting the oxidative stress level. Mediation a*b effect investigates whether regional gray matter volume plays the role of mediator between the oxidative stress level and perceptual functions. In addition, path c’ and c represent the total relationship between oxidative stress and perceptual functions with/without adjustments to regional gray matter volume, respectively. PIQ performance intelligence quotient, TBARS thiobarbituric acid reactive substances, VBM voxel-based morphometry