A visit to the spa, circa 2015: Your session begins with a battery of mental tests—from visual puzzles to memory quizzes to games that measure reaction time. After your results are evaluated, you don a lightweight helmet housing electromagnetic coils and relax while a certified “neurotrainer” consults a 3-D image of your brain to adjust the helmet settings. You feel oddly energized as the device zaps your gray matter with painless energy pulses. After a few minutes, you visit the smart bar for a custom regimen of brain-enhancing pills.