To explore local variation, we identified unique transcriptional signatures by analysis of variance (ANOVA) for the hippocampus. Following unsupervised hierarchical 2D clustering, cytoarchitecturally discrete subdivisions of the hippocampus (dentate gyrus, CA fields and subiculum) showed distinctive expression patterns sufficiently robust to cluster together like-samples while distinguishing subdivisions from one another (Fig. 5a). Interestingly, samples from the CA3 and CA4 subfields were not discriminable (intermixing in Fig. 5a), consistent with the view that CA4 is not a functionally distinct subfield from CA322). Similarly robust regional clustering was observed in the mesencephalon, pons and myelencephalon (Supplementary Fig. 6 and Supplementary Table 9). Differential expression across hippocampal subfields could be validated by ISH. For example, the calcium-binding protein CALB1 has strong selectivity for the dentate gyrus relative to other hippocampal subdivisions in both brains (Fig. 5b), and cellular specificity for dentate gyrus granule neurons is demonstrated on an independent adult brain specimen by ISH in Fig. 5c. Hippocampal ISH data for CALB1 generated with the same histology platform in adult mouse1 and rhesus macaque23 allowed a phyletic comparison. Interestingly, expression in human differs
