GPHN and Alzheimer disease: The ratio of the peaks of the immunolabeling frequency distributions for PSD-95 to GPHN (PSD-95-ir/GPHN-ir), for each subject, was not different between groups for layer 1 (Welch ANOVA allowing unequal variances, P = 0.22), indicating a similar anatomical E/I ratio for AD and DS versus controls (Fig. 3a).