Cube and Necker cube scores were used as covariates. Subtraction analysis revealed more extensive loss of GM in the left middle frontal gyrus in the no-IMP subgroup at baseline, relative to the IMP subgroup (Figures 1A,B and Table 3). Analysis of MMSE scores at the 6-month follow up revealed that changes in MMSE scores were positively correlated with volume in the left middle frontal gyrus (Figure 1C and Table 3). Subtraction analysis revealed more extensive GM loss in the anterior cingulate gyrus and left middle frontal gyrus in no-IMP participants in both the ExM (Figure 2A and Table 3) and CS (Figure 2B and Table 3) groups at baseline, respectively.