CNS age-related gene expression patterns. (a) For any given gene there are six possible patterns of gene expression from young to middle-aged to old. For approximately 95% of the genes, there was no significant change (p < 0.05 and Z-ratio ≥ 1.50 or ≤ -1.50) in expression across ages (pattern 1). For most CNS regions, pattern 2 (change from middle-aged to old) was the most common. Red, upregulated; blue, downregulated. (b) Comparison of the numbers of genes that were significantly affected by age in each CNS region. The transcriptomes of the cortex, hippocampus and spinal cord were the most responsive to age, while the transcriptome of the striatum was stable over time. The spinal cord transcriptome was remarkable for the large number of genes significantly upregulated with advancing age, in contrast to other CNS regions in which most genes were downregulated with advancing age. Gene lists are in Table S2a,b in Additional data file 1.