Tau transgene expression affects dendritic spine morphology. a-a’ In vivo imaged dendritic spines (a maximum intensity projection) were reconstructed (a’, 3D wireframe graphics) and classified into mushroom (red), stubby (green), and thin spines (blue) based on morphological parameters using Imaris software. Scale bar: 2 μm. b-d In P301S Tau mice, the spine head volume was enlarged (b) and the spine length was increased (c), causing a shift in the fractions of morphological spine classes (d). Presented are means ± SD of 3–4 mice; 130–167 spines on 10 dendrites per group; 32–45 spines on 2–4 dendrites per mouse. Unpaired t test of log-transformed data (b), unpaired t test (c, d); * p < 0.05.