Extended Data Fig. 3: Synaptic connectivity increases with empirical signal correlations measured directly in vivo rather than via the digital twin.

a, Mean in vivo signal correlation is different (mean ± sem, paired t-test) for connected pairs, ADP controls, and same area controls for all projection types, as in Fig. 2d. b, Axon-dendrite co-travel distance (μmL_d) increases in a graded fashion with in vivo signal correlation for all projection types, as in Fig. 2e. c Synapse density (N_syn/mmL_d) increases in a graded fashion with signal correlation, for all projection types, as in Fig. 2f. The shaded regions in b and c are bootstrap-based standard deviation. d, Synapse size (log₁₀ cleft volume in voxels) is positively correlated with in vivo signal correlation after regressing out L_d (p-value by linear regression), as in Fig. 2h. e, In vivo signal correlations increases with number of synapses after regressing out L_d (p-values by linear regression), as in Fig. 2j. f, Area/layer joint membership breakout as in Fig. 4 for in vivo signal correlations at axonal scale. g, Area/layer joint membership breakout as in Fig. 4 for in vivo signal correlations at synaptic scale. h, Comparison of the observed and expected postsynaptic functional similarity as in Fig. 5 for in vivo signal correlations. (For all panels, * = p-value < 0.05, ** = p-value < 0.01, *** = p-value < 0.001, multiple comparison correction by BH procedure. For statistics and sample sizes, see Supplementary Tables 23–28).