Figure 6.

Comparison of the number of gray matter divisions for each depth of division of the central nervous system (CNS) according to its structural divisional hierarchy arranged topographically in Rat Brain Maps 4.0 (BM4) (Swanson, 2018), compared for the rat (based on BM4), and the mouse (based on the Allen Reference Atlas, ARAv1) (Dong, 2007). The upper chart (a) compares 9 depths of CNS divisions above the level of gray matter region (parent divisions) beginning with CNS at depth 1. The lower chart (b) shows the total numbers for all gray matter divisions (All divisions), and for the gray matter division categories of parent division (Parent), gray matter region (Region), and gray matter subregion (Subregion; including sub-subregion divisions, but excepting divisions that layers of cerebral and cerebellar cortical regions that apply similarly to rat and mouse). In general, ARAv1 has fewer gray matter divisions in each category (b) and at each depth of CNS division (a) compared to BM4, primarily due to a more coarse-grained parcellation. The retina (1 gray matter region) and spinal cord (22 gray matter regions) were not included in ARAv1 but were included in BM4; however, BM4 numbers for these divisions are included with the ARAv1 numbers here (and on MsBFv1 where they are present) to avoid exaggerating differences that were not due to these omissions. Conversely, to avoid understating differences, subregions that are laminar divisions of gray matter regions in the cerebral cortex and elsewhere (and present in both rat and mouse), are not included. Despite fewer ARAv1 gray matter divisions compared to BM4, the overall distribution is quite similar, reflecting a high-level of similarity in the underlying parcellation as represented in the reference atlases (see Supporting Information 3, and text for details).