In 2015, a team at Johns Hopkins published a study about volunteering that reads more like a study about brains.
They took 111 people, average age sixty-seven, and drew lots. Half were placed in Baltimore public schools for fifteen hours a week, helping children learn to read in libraries that were short-staffed. The other half went on with their lives as they were. Everyone had their brain scanned at the start, again after a year, and again after two.
The people who stayed home had brains that did the ordinary thing. They shrank. Past sixty-five, that runs somewhere between 0.8 and 2 percent a year, and it happens to everyone.
The men in the schools went the other way. Their brain volume rose — between 0.7 and 1.6 percent over the two years, in the regions that go first in Alzheimer’s disease. The women in the program held roughly level, with small gains that didn’t reach statistical significance, against a decline of about 1 percent in the group that stayed home. And the people whose v…