Walk Briefly
You don’t even have to do anything fancy:
[R]esearchers randomly assigned 120 healthy but sedentary men and women (average age mid-60s) to one of two exercise groups. One group walked around a track three times a week, building up to 40 minutes at a stretch; the other did a variety of less aerobic exercises, including yoga and resistance training with bands.
After a year, brain scans showed that among the walkers, the hippocampus had increased in volume by about 2 percent on average; in the others, it had declined by about 1.4 percent.
Our tiny brains ask for so little. “Please,” they whisper. “Shut up,” we say. “Help me solve this Jumble.”