After five weeks, all of the animals, including an untouched control group, were loosed individually into a brightly lit maze with a single, darkened chamber. Rodents gravitate toward dark places and during repeated visits to the maze, the animals would be expected to learn the location and aim for that chamber.

But their success differed. In the first few tests, the control animals were fastest and most accurate, and the rodents with mild cognitive impairments faltered. With a little practice, though, the weight-trained animals, despite their induced cognitive impairments, caught up to and in some cases surpassed the speed and accuracy of the controls.

The weight training had “effectively restored” their ability to think, Mr. Kelty says.

The untrained animals with mild cognitive impairments, meanwhile, continued to lag far behind the others in their ability to find and recall the chamber.

Finally, to better understand how ladder climbing might have changed the rats’ brains and minds, Mr. Kelty and his collaborators microscopically examined brain tissue from each of the groups. As expected, they found signs of inflammation in the brains of the animals that had been injected.

But they found, too, that the memory centers of the brains in the weight trainers teemed now with enzymes and genetic markers that are known to help kick-start the creation and survival of new neurons, while also increasing plasticity, which is the brain’s ability to remodel itself.

In effect, the brains of the weight-trained rats were remaking themselves to resemble those of brains that had not been inflamed and impaired.

Of course, this was a study with rats, and rats are not people. We rarely weight train by climbing ladders with heavy bags strapped to our rears, for one thing. So, it is impossible to know from this experiment if our brains will respond in quite the same way to lifting weights.