At the end of this short paragraph, stop reading. Close your eyes. Imagine yourself hitting a tennis ball. Do it again.

Can you see yourself hitting the ball? Can you visualize its arc through the sky? Does it veer off course, and can you imagine yourself hitting it better next time?

If so, you are using a technique that has helped many people survive prison. Edith Bone, a professor of medicine and a translator who spoke six languages fluently, constructed an abacus out of stale bread and made an inventory of her sprawling vocabulary while imprisoned in Hungary after World War II. Hussain Al-Shahristani, Saddam Hussein’s former chief scientific adviser, spent a decade in solitary confinement at the Abu Ghraib prison near Baghdad. He survived, according to the BBC, by “taking refuge in a world of abstractions, making up mathematical problems, which he then tried to solve.” He is now Iraq’s minister of higher education and scientific research. While imprisoned in a German concentration camp during World War II, the Russian Jewish mathematics professor Jakow Trachtenberg watched as his fellow prisoners “gave up hope and died even before being sent to their death.” To survive, he developed an innovative method of performing rapid mental calculation, known today as the Trachtenberg system.

Summoning up mental imagery is a “quasi-perceptual experience,” according to the Concise Corsini Encyclopedia of Psychology and Behavioral Sciences. It stimulates the brain’s frontal lobe, which is associated with higher cognitive processes and abstract thought—as well as perception and motor control. That can make it feel real. “Cognitive operations performed on images, such as mental scanning or distance comparisons, exhibit … patterns similar to those executed on images that reactivate stored visual information,” says Emmanuel Mallet, a cognitive neuroscientist at the French National Centre for Scientific Research.