The findings of their subsequent follow-up experiment, however, were even more intriguing and consequential. In that study, which appears in this month’s issue of The Journal of Physiology, the researchers studied animals after a single bout of exercise and also after four weeks of regular, moderate-intensity running.

After the single session on the treadmill, the animals were allowed to rest and feed, and then their brain glycogen levels were studied. The food, it appeared, had gone directly to their heads; their brain levels of glycogen not only had been restored to what they had been before the workout, but had soared past that point, increasing by as much as a 60 percent in the frontal cortex and hippocampus and slightly less in other parts of the brain. The astrocytes had “overcompensated,” resulting in a kind of brain carbo-loading.

The levels, however, had dropped back to normal within about 24 hours.

That was not the case, though, if the animals continued to exercise. In those rats that ran for four weeks, the “supercompensation” became the new normal, with their baseline levels of glycogen showing substantial increases compared with the sedentary animals. The increases were especially notable in, again, those portions of the brain critical to learning and memory formation — the cortex and the hippocampus.

Which is why the findings are potentially so meaningful – and not just for rats.

While a brain with more fuel reserves is potentially a brain that can sustain and direct movement longer, it also “may be a key mechanism underlying exercise-enhanced cognitive function,” says Hideaki Soya, a professor of exercise biochemistry at the University of Tsukuba and senior author of the studies, since supercompensation occurs most strikingly in the parts of the brain that allow us better to think and to remember. As a result, Dr. Soya says, “it is tempting to suggest that increased storage and utility of brain glycogen in the cortex and hippocampus might be involved in the development” of a better, sharper brain.