Researchers have discovered that paternal mice that physically interact with their babies grow new brain cells and form lasting memories of their babies. Scientists determined that when paternal mice interact with their newborn babies, new brain cells develop in the olfactory bulb—the part of the brain responsible for sense of smell, and in the hippocampus, which is responsible for memory. Weeks after the fathers are separated from their babies, they can still recognize their offspring from unrelated mice. The study may have implications for long-term mental health.