Mothers who have specific fears and anxieties may inadvertently pass them along to their days-old newborns through an unlikely method--smell. A new study published in the journal Proceedings National Academy of Sciences tested the role of smell in fear transfer by exposing rats to mild shocks while they were in an environment scented with peppermint oil. Later, the same rats gave birth, and the pups' fear responses were tested, measuring the activity of the part of the brain called the amygdala, when they were exposed to the same scent. The pups, the study found, showed a fear reaction at the mere whiff of peppermint.
"It was really surprising to us that...it could be so early and could be so lasting," said [psychiatrist, neuroscientist, and lead researcher Jacek] Debiec, pointing out that infants generally do not form lasting memories unless experiences are repeated during the first few days of life, a concept called infantile amnesia. "Here it was a single exposure and it was enough for these newborn pups to create lasting memories," added Debiec.
When researchers gave pups a substance that blocked activity in the amygdala, according to the study, the baby rats did not learn the fear of peppermint smell from their mothers. This could help mental health experts find ways to prevent children from learning certain fear responses from their mothers.
"Infants can learn from their mothers about potential environmental threats before their sensory and motor development allows them a comprehensive exploration of the surrounding environment," says the six-page study.
Some mother rats tried to plug the tubing so that the smell wouldn't come through, a behavior that Debiec found interesting and wants to study further.
Image: Boy smells something bad, via Shutterstock