The largest contact holds a mean 47% of cleft size in 1,519 selected Allen V1 connections

We measured contact size concentration in one Allen V1 Deep Dive mouse volume. We reused a verified table of excitatory contacts and selected 1,519 connections with at least three observed contacts. The largest contact held a mean 46.72% of total cleft size. One contact held more than half in 499 connections. Mean size-weighted effective count divided by contact count was 0.8278. Under an independent contact dropout model with linear size weights and equal survival probability, equal weights underestimate normalized variance by a mean factor of 1.2432. Observed sizes were more balanced than broad shuffles that preserved one cell, both cell types, and contact count. Position control removed clear separation for the source shuffle and left few movable contacts. These conditional results do not isolate a connection-specific process. One animal, incomplete arbors, size as a proxy, and no matched physiology limit the result. The package includes contact evidence, source code, null draws, provenance, a figure, and an independent audit.

Allen Institute · connectomics · contact size · structural robustness · conditional permutation · dropout model