What does an infant human have in common with a rat pup? More than you may think, according to Regina Sullivan, a research professor at the NYU Child Study Center, and Gordon Barr, a psychology professor at Hunter College.

Both rat pups and infants show advanced learning and an attachment to their caregivers, Sullivan said.

"I started by assessing neurobiology and how a rat brain works differently than an infant brain," she said.

In her previous research, Sullivan found that odors associated with the mothers suppress the release of corticosterone, a stress hormone, in rat pups. But Sullivan's new study showed that corticosterone suppression actually reduces levels of the neurotransmitter dopamine in the brain's "fear center."

Sullivan said that during the new study she conducted, the rats observed rats were acting illogically: If a scent was paired with something aversive, the rats would learn to like that scent. According to Sullivan, the scent is a way for the rat pups to identify their mothers.

"Rat [pups] can't see or hear," she said. "The odor of the mother helps the rat find his mother. Without that odor, the rat would be unable to survive."

The reason rat pups do not avoid this smell and seek it instead lies in the part of the brain known as the amygdala, according to Sullivan. The amygdala of the infant rat is very different from that of an adult rat — adult rats have more dopamine in their amygdala than infant rats. That means the brain has a specific mechanism to prevent the infant from learning to avoid its mother's odor.