Synapses between neurons control the the strengths of neuronal communication in neural circuits and their strengths are in turn dynamically regulated by experience. Because dendritic spine head volumes are highly correlated synaptic strength [1], anatomical reconstructions can probe the distributions of synaptic strengths. Synapses from the same axon onto the same dendrite (SDSA pairs) have a common history of coactivation and have nearly the same spine head volumes, suggesting that synapse func…