Mean delay increased with cell-body distance within outputs from the same inhibitory source in selected Allen mouse slices

We tested whether the distance-delay relation remains within outputs from the same source cell. We used linked cell and connection records in the Allen Synaptic Physiology r2.1 small database. We matched outputs by source cell and target nonsynaptic class, then fit delay against distance after subtracting each matched mean. The main mouse inhibitory sample had 328 connections, 151 source cells, and 113 inferred donors. Delay increased by 0.337 ms per 100 micrometres. The 95% donor bootstrap interval was 0.191 to 0.497; the nominal four-group 98.75% interval was 0.152 to 0.544. The result remained positive with target layer matching, log delay, and removal of missing target classes. Human inhibitory outputs also had a positive estimate, but only eight donors supplied the main sample. Both excitatory groups had intervals that included zero. The mouse result shows that differences between source cells alone do not account for the observed distance relation. It does not identify axon conduction speed, causation, or a rule across regions and behavior.

synaptic latency · branching circuits · within-cell comparison · Allen Institute · cell-body distance