Ten percent to 15% of glucose used by the brain is metabolized nonoxidatively despite adequate tissue oxygenation, a process termed aerobic glycolysis (AG). Because of the known role of glycolysis in biosynthesis, we tested whether learning-induced synaptic plasticity would lead to regionally appropriate, learningdependent changes in AG. Functional MRI (fMRI) before, during, and after performance of a visual-motor adaptation task demonstrated that left Brodmann area 44 (BA44) played a key role in adaptation, with learning-related changes to activity during the task and altered resting-state, functional connectivity after the task. PET scans before and after task performance indicated a sustained increase in AG in left BA 44 accompanied by decreased oxygen consumption. Intersubject variability in behavioral adaptation rate correlated strongly with changes in AG in this region, as well as functional connectivity, which is consistent with a role for AG in synaptic plasticity.T he resting brain's energy needs are supported almost entirely by the metabolism of glucose to carbon dioxide and water (1). The first step of this process, glycolysis, requires no oxygen whereas the second step, oxidative phosphorylation, does. In the normal adult human brain, 10-15% of the glucose never reaches the second step-it is shunted away from oxidative phosphorylation despite the presence of adequate oxygen (2-5). This process is commonly referred to as aerobic glycolysis (AG).Several roles for AG have been identified, including biosynthesis (for recent reviews, see refs. 6-8), the regulation of cellular redox states (9, 10), the regulation of apoptosis (11), the provision of ATP for membrane pumps (12)(13)(14), and the regulation of cell excitability (15, 16). More recently, similar functions of AG have been observed in the posttranscriptional control of T-cell effector function (17, 18), an observation now extended to the microglia (19), where it is associated with an activated state related to inflammation as well as synaptic pruning.In the developing human brain, at a time when synaptic growth rates are highest (approximately age 10), total glucose consumption is twice that of the adult, and 30% of that glucose consumption is AG (a recent summary of this early literature is contained in ref. 20), suggesting an important role in brain development. Another remarkable feature of AG in the adult human brain is that it varies regionally (21): nearly 25% of resting glucose consumption in the medial prefrontal cortex is AG whereas AG constitutes as little as 2% glucose consumption in the cerebellum and medial temporal lobes. Correlation of these regional data with regional gene expression in the adult human brain revealed increased gene expression typical of infancy (i.e., neotony) that is related to synapse formation and growth (20).Further supporting the link between AG and plasticity are findings demonstrating that lactate, released by astrocytes and taken up by neurons, is critical for memory formation. Neuronal uptake of lactate ch...