Human evolution is characterized by the rapid expansion of brain size and drastic increase in cognitive capabilities. It has long been suggested that these changes were accompanied by modifications of brain metabolism. Indeed, human-specific changes on gene expression or amino acid sequence were reported for a number of metabolic genes, but actual metabolite measurements in humans and apes have remained scarce. Here, we investigate concentrations of more than 100 metabolites in the prefrontal and cerebellar cortex in 49 humans, 11 chimpanzees, and 45 rhesus macaques of different ages using gas chromatography-mass spectrometry (GC-MS). We show that the brain metabolome undergoes substantial changes, both ontogenetically and evolutionarily: 88% of detected metabolites show significant concentration changes with age, whereas 77% of these metabolic changes differ significantly among species. Although overall metabolic divergence reflects phylogenetic relationships among species, we found a fourfold acceleration of metabolic changes in prefrontal cortex compared with cerebellum in the human lineage. These human-specific metabolic changes are paralleled by changes in expression patterns of the corresponding enzymes, and affect pathways involved in synaptic transmission, memory, and learning.H uman evolution is characterized by rapid expansion of brain size and increase in cognitive capabilities, leading to the emergence of unique and complex cognitive skills. These changes have long been associated with changes in brain metabolism, in particular with respect to increased energy demand (1). Large brains are metabolically costly. Thus, humans allocate approximately 20% of their total energy to the brain, compared with 11-13% for apes and 2-8% for other mammalian species (2). This increased metabolic demand has been associated with elevated expression of genes involved in neuronal functions and energy metabolism (3, 4). These changes may have been evolutionary advantageous, as indicated by signatures of positive selection reported for the amino acid changes, which occur in the mitochondrial electron-transport chain proteins, in anthropoid primates and humans, as well as elevated expression of the energy metabolism pathways in the human brain (5, 6). On the histological level, human brains show the largest density of glia cells relative to neurons in the prefrontal cortex, which provides an indirect indication of increased neuronal metabolic demand (7).Changes in brain metabolism are also implicated in neuropsychiatric disorders, such as schizophrenia, which affect some of the human-specific cognitive abilities (8, 9). Furthermore, direct measurements of 21 metabolites in the prefrontal cortex of adult human controls compared with human schizophrenia patients, chimpanzees, and rhesus macaques, carried out using proton NMR spectroscopy have shown significant overlap between human-specific evolutionary changes and metabolic differences between controls and schizophrenia patients (10). Notably, this study has identified not ...
