A baby's smile is known to melt a mother's heart, but now new research shows that it also lights up her brain.
Researchers at Baylor College of Medicine in Texas looked at brain scans of first-time mothers as they looked at photos of babies -- their own and others who were either smiling or crying.
They found that when mothers were presented with images of their own babies smiling, their brains reacted differently than they did at any other time by activating "reward centers" of the brain -- evidence, scientists say, that supports the theory that mothers are biologically programmed to care.
"The smile just by itself -- just by seeing it -- is a powerful social reward," said Dr. Ross Thompson, a professor of psychology at the University of California at Davis. "And it's a social reward, especially for mothers who are invested in helping that baby feel good."
According to the research, when a mother sees her baby smiling, the neurotransmitter dopamine is released in her brain, resulting in a natural high.
Thompson told "Good Morning America" that the effect can go beyond just human babies as well.
"There is really something special about cues of babyishness," he said. "We respond with warmth to puppies and kittens and they have some of those same cues. They have large heads; they have large eyes; they have rounded facial features just like human infants do. This natural warmth we have toward infants is biologically deeply rooted in us."
Oddly, researchers found that mothers had no increased response to the pictures of their babies crying.