AP CSI distributions across the brain for different age and genotype groups. The CSI is defined as the number of input neurons normalized by the number of starter neurons; the AP positions are given relative to bregma values. Representative input regions were used for the AP plot, including the CA1_py layer, MS-DB, thalamus, RSC, Vis cortex, Aud cortex, and SUB. A, WT young group (n = 8). B, WT middle-age group (n = 10). C, 5xFAD young group (n = 10). D, 5xFAD middle-age group (n = 12). The red dashed line at AP = −3.52 mm shows the position of the viral injection site. There is a significant difference in the CA1_py distribution between WT young and 5xFAD middle-age groups (paired Wilcoxon rank-sum test, p = 1.67 × 10⁻⁶).