Extended Data Fig. 1: Workflow of tissue collection.

a, The right hemisphere coronal slab was mounted on a metal plate with an OCT compound with the top (rostral) surface of the slab parallel to the plate. Created in BioRender. Mosharov, E. (2025) https://BioRender.com/z524941. b, After affixing the plate to the computer numerical control (CNC) cutting area, the top surface was cleaned with a 12.7 mm flat-tip drill bit rotating at 100 RPM and moving horizontally at 300 mm/sec. After cleaning 1 mm from the top, morphological brain structures were clearly visible and the surface was parallel to the plane of drill bit movement, ensuring that voxels will be of a uniform height. c, A 3 × 3 mm grid was milled with a 0.4 mm drill bit rotating at 10,000 RPM and moving horizontally at 250 mm/min. During a single pass, 0.2 mm of the depth was milled, requiring 15 passes to reach the desired 3 mm of cut depth and a total distance of ~70 m. Total milling time for a 130.8 ×61.25 mm hemisphere was 4 h and 38 min. d, Fully milled slab was placed on dry ice. First, four samples of shavings were collected from the surface above one white and three gray areas (Extended Data Fig. 2). Next, shavings were gently removed from the surface with a brush and a pre-chilled scalpel and forceps were used to collect 703 individual voxels. e, Following sample collection, slab surface was cleaned once more with a 12.7 mm drill bit. f, The metal plate with the slab was then mounted on a freezing microtome and several 50 µm-thick cryosections were collected for histological evaluation. g, Summary of the steps during the collection of brain voxels and thin sections. Letters on the right refer to images shown on the corresponding panels. h and i, Thin brain section stained with Nissl to show neurons and glia either alone (h) or in combination with an immunostaining against neuronal nuclear antigen NeuN to highlight neuron-enriched areas (i).