Figure 2. Brain AG topography changes with normal human aging.

The normalized data for each metabolic parameter and each individual was Spearman rank correlated with an average data set comprising participants aged 20 – 23 years. For CBF (yellow), CMRGlc (pink), and CMRO₂ (orange), the Spearman rank correlation remained high throughout the lifespan (CMRGlc minimum Spearman’s rho = 0.92, CMRO₂ min rho = 0.89, CBF min rho = 0.91), suggesting that the topography for these aspects of brain metabolism remains relatively stable throughout the adult lifespan. The Spearman rank correlations for AG (blue) for each participant instead shows significant decreases with age (Pearson’s r = −0.64, p < 2×10⁻¹⁶), remaining only modestly similar to the young adults among the oldest participants. High inter-individual variability is evident for AG, particularly among the older participants. These changes in AG topography are in part due to whole brain changes in AG and in part due to topographical changes between CMRGlc and CMRO₂ (see Figure S4 for details).