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Aerobic exercise can reverse age-related brain shrinkage. In older adults, just one year of regular aerobic activity increased hippocampal volume by 2%, effectively restoring 1–2 years of brain loss. This highlights the remarkable ability of exercise to counteract brain aging. But does intensity matter? In a recent study, mice doing HIIT experienced an impressive 85% increase in new brain cells in the hippocampus—an area critical for learning and memory. What’s even more remarkable is that HIIT didn’t just boost neurogenesis in the hippocampus—it drove a 155% increase in new brain cells within the ventricular-subventricular zone, a brain region involved in olfaction, or the sense of smell. That’s nearly double the effect seen with moderate exercise. So, what makes HIIT such a powerful stimulus for neurogenesis? It turns out that lactate—a metabolite produced during intense exercise—plays a crucial role. When researchers removed the receptor for lactate, called HCA1, mice no longer experienced the same surge in new brain cells. We now have overwhelming evidence that lactate isn’t just a byproduct of exertion—it’s a key signal that helps drive brain plasticity. DOI: 10.1113/JP287328 Human study PMID: 21282661