Caloric restriction (CR) prolongs lifespan and retards many detrimental effects of aging, but its effect on brain mitochondrial function and neuronal activity--especially in healthy aging--remains unexplored. Here we measured rates of neuronal glucose oxidation and glutamate-glutamine neurotransmitter cycling in young control, old control (i.e., healthy aging), and old CR rats using in vivo nuclear magnetic resonance spectroscopy. We found that, compared with the young control, neuronal energy production and neurotransmission rates were significantly reduced in healthy aging, but were preserved in old CR rats. The results suggest that CR mitigated the age-related deceleration of brain physiology.