4.2.3.1 PCA
## [1] "Intercept"
## [2] "tissue_region_Hippocampus_vs_Frontal.cortex"
## [3] "tissue_region_Pituitary.gland_vs_Frontal.cortex"
## [4] "group_Fluoxetine_vs_Control"
## [5] "group_Acupuncture_vs_Control"
## [6] "group_model.of.depression_vs_Control"