The brain is a complex organ that is comprised of several anatomical substructures. The literature contains evidence indicating the high variability of gene expression in distinct sites in the brain tissue. Studies that present data on transcriptome variation across brain regions suggest that the cerebellum has the most distinguishable gene expression pattern compared with other brain substructures (Lockhart & Barlow, 2001; Roth, et al., 2006; Strand, et al., 2007). Variation in gene expression across brain regions is related to both functional and anatomical differences in its substructures. Moreover, studies involving animal models show that gene expression appears to correlate with performance (e.g., on motor tasks) in some brain substructures, such as the cerebellum, amygdala, and hippocampus (Nadler, et al., 2006). Significant differences in the cell composition of the various anatomical brain substructures result in cell-specific differences in gene expression (Colantuoni, et al., 2000). For example, it has been shown that genes involved in the regulation of glutamate receptor signaling pathways are especially enriched in their expression in the cerebellum, which contains a large number of glutamatergic granule cells— small cells
