It's possible that calorie-restriction early in life helped cushion the brain from later aging, in line with research that has linked eating less with longer lifespans. But Barnes suspects that non-biological explanations are more likely.
Very few white people in the study reported extreme adversity as children, for one thing, possibly making the sample size too small to detect any relationships in that group.
As for the African-Americans, those who were still alive in their 60s, 70s, 80s and beyond likely represent the hardiest members of a population that came of age before the civil rights movement when there were few opportunities available to them.
"One of the things we know is that African-Americans live sicker and die younger than Whites," said Tené Lewis, a psychosocial epidemiologist at Emory University's Rollins School of Public Health in Atlanta. "When you get to age 65, which is the baseline in the new study, you're already dealing with a heartier African-American population. These are people who, no matter what you throw at them, are particularly resilient."