Orientation-invariant morphometry reveals a continuum of dendritic spine forms in layer II pyramidal neurons of the petavoxel human connectome

A recent study (Manjarrez et al., 2026) showed that the classification of cortical dendritic spines into stubby, thin, and mushroom subtypes is unstable under rotation. That result criticizes the categorical scheme but leaves an open question. What is the actual structure of spine morphology once the viewing angle is controlled? Here we answer it. We analyzed 228 spines from layer II pyramidal neurons in the H01 nanometer-resolution reconstruction of human temporal cortex. We first quantified the source of instability. We found that rotating dendritic segments by 90 degrees about their axes shifted the apparent spine height and head width in opposite directions across the population, thereby