People who donate kidneys to total strangers aren't just bighearted, they're big-brained compared to most people, researchers say. Neurologists scanned the brains of 39 such donors and found that their brains were 9% bigger than non-donors' brains—with significantly greater volume in the part of the brain that deals with emotion and empathy, reports the Los Angeles Times. In psychopaths, the same part of the brain is much smaller than normal. The altruistic donors were also better able to read facial expressions, not too much above average, but at "the high end of the capacity for compassion and emotional sensitivity, which is sort of encouraging" because it suggests many other people are capable of such selfless acts, says lead researcher Abigail Marsh.
Marsh says that, in retrospect, she shouldn't have been surprised to find that the donors were "delightful study participants" who showed up hours early for appointments and were reluctant to accept payment for travel expenses because they didn't want to take money away from scientific research. One participant, a DC-area man who gave a kidney to an Ethiopian refugee, says this isn't the first time people have been curious about his brain: He was extensively quizzed when he first signed up for the donor program. "The first test they gave me? Let's send this guy to a psychiatrist because who wakes up one day and says, 'Hey, let's start giving away body parts!'" he tells WTOP. (Read about how Facebook helped one 2-year-old get a new kidney.)