Unlike humans, rodents seem to inherently enjoy physical activity, and Cotman’s mice ran several kilometers a night. They were divided into four groups: mice running for two, four, or seven nights, and one control group with no running wheel. When their brains were injected with a molecule that binds to BDNF and scanned, not only did the scans of the running rodents show an increase in BDNF over controls, but the farther each mouse ran, the higher the levels were. When Cotman saw the results—that the spike occurred in the hippocampus—he didn’t believe them himself: “I said, No, c’mon guys, we
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