Our extensive neocortical sampling allowed us to investigate transcriptional variation across the neocortex in relation to spatial position and functional parcellation. Although highly differential expression between cortical regions is much less pronounced than between other brain regions (Fig. 4), many genes show statistically significant variation between lobes or gyri at a lower threshold. We first identified the 1,000 genes displaying the most significant variation in expression between 56 gyri in both brains (ANOVA, P < 0.01 BH-corrected, ranked by fold change between gyri; Supplementary Table 10). We then performed principal component analysis (PCA) on the 1,000 (genes) by 56 (sampled gyri) matrices for both brains. As shown in Fig. 6a–c, the first three principal components had striking selectivity for specific cortical regions (samples ordered by lobe and roughly rostral to caudal within each lobe) and were generally reproducible across both brains. PC1 is associated with primary sensorimotor cortices, with relative differential expression in precentral (motor) and postcentral (somatosensory) cortex, Heschl’s gyrus (primary auditory) and primary and secondary visual areas. Confirmation of the visual cortex enrichment by ISH for several synaptic
