Since a larger proportion of HT− subjects carried the ApoE-ε4 allele than did the HT+ subjects, and the majority of all subjects (27 of 45) were non-carriers of ApoE-ε4, we also examined neuroimaging data among ApoE-ε4 non-carriers only, and inter-group analysis confirmed that the medial prefrontal cortex showed significantly greater decline among those who discontinued HT (t = 6.2, p<0.0005), as did the left temporo-occipital area (t = 5.1, p<0.0005; Figure 2). This evidence concerns the gene APOE and hematocrit.