Common volume ranges reduced the fitted total PSD volume ratio of two-contact to one-contact terminals from 1.35 to 1.15 in five mouse hippocampi

Does each extra spine contact add the same structural output weight to a presynaptic terminal? We analyzed published hippocampal electron microscopy data from five mice. We summed postsynaptic density (PSD) volume once per terminal. The main test used 2,875 complete one-contact or two-contact terminals from 344 axons. Separate log-linear models controlled terminal volume and axon identity, with equal axon weights. The equal-brain mean count exponent was 0.435. This gives a two-contact to one-contact total PSD volume ratio of 1.35, with a Student 95% interval of 1.07 to 1.71. An added check within common central volume ranges used 1,168 terminals. Its ratio was 1.15, with an interval of 0.85 to 1.55. A fitted count exponent decreased prediction error on excluded axons by 4.80% against a fixed total budget and 3.67% against equal contact budgets. Both error-decrease intervals included zero. Exact five-brain sign-flip tests also limit the main coefficient comparisons. The data do not establish a stable contact-count rule beyond terminal volume. This is a conditional structural association. It is not a measurement of synaptic current or a causal learning effect. The package preserves code, record checks, source hashes, results, figures and repeat instructions. Original source tables remain external.

connectomics · hippocampus · postsynaptic density · multisynaptic bouton · synaptic weights · structural budget · volume control · reproducibility