Fig 5. Spine and bouton volume correlate closely with synapse size in the aged and adult neuropil.

A, Histogram showing the distribution of vesicle density normalized to the synaptic contact surface area shows no difference between aged and adult animals (p = 0.4, Kolmogorov-Smirnov test). B, Correlation between spine head volume and synaptic surface area for adult (N = 207; R² = 0.673) and aged (N = 197; R² = 0.817) mice. The slopes are not significantly different (ANOVA, p = 0.42). C, Correlation between volume of excitatory boutons and synaptic surface area for adult (N = 169; R² = 0.369) and aged (N = 146; R² = 0.526) mice. The slopes are significantly different (ANOVA, p = 0.0045).