A fixed rank test found no clear extra calcium coincidence in spine triplets within 5 µm in 18 mice

Nearby synaptic inputs can act together on a dendrite. We asked if groups of three nearby spines had more large calcium amplitudes on the same trial than spread groups. We used public visual cortex data from mice. We ranked signed amplitudes within each stimulus direction and marked the two largest of eight to ten common trials. The main test used 539 compact triplets and 42,634 spread triplets in 178 fields from 21 neurons and 18 mice. All pairs had no separating branch point and were at least 2 µm apart by path and straight-line distance. Compact spans were less than 5 µm. Spread spans were 10 to less than 20 µm. The compact-minus-spread excess over independent rank placement was 0.117 percentage points. The 95% mouse bootstrap interval was −0.062 to 0.302 points. The two-sided mouse sign-flip p value was 0.240. An exact split gave 0.017 points from pair covariance terms and 0.100 points from a third central product. The third-product contrast was 0.048 points after removal of a field median signal, with an interval that included zero. A specified wider-span check gave a small positive result. It is secondary and uses a larger sample. The package provides a new triplet benchmark, all input arrays, source checks, code and figures. The test did not establish a compact-group advantage. These one-second calcium amplitudes do not identify spike synchrony, synaptic weights or a unique three-input mechanism.

dendritic spines · calcium imaging · trial ranks · joint activity · synaptic input · visual cortex · reproducible benchmark