A study conducted by researchers at the University of Michigan and published in the Proceedings of the National Academy of Sciences found that mothers may emit odors that teach their infants what to be afraid of, even if the fearful experience is one that the baby has never been exposed to.
The research may help explain a phenomenon that has perplexed scientists for generations: Children may have intense trauma reactions to events that they never experienced, but that their parents did. For example, children of Holocaust survivors often exhibited nightmares, flashbacks, and avoidance behaviors associated with their parents’ experiences, even if those happened before the children were born.
Researcher Dr. Jacek Debiec, who has studied grown children of Holocaust survivors, says these reactions seem too deeply rooted to be the result of simply having heard stories about the frightening events.
“Our research demonstrates that infants can learn from maternal expression of fear, very early in life,” Dr. Debiec said. “Before they can even make their own experiences, they basically acquire their mothers’ experiences. Most importantly, these maternally transmitted memories are long-lived, whereas other types of infant learning, if not repeated, rapidly perish.”
In the study, non-pregnant rats were exposed to an unpleasant electric shock whenever they smelled peppermint. After the rats became pregnant and gave birth, the researchers again exposed the mother rats to peppermint smell, this time in the presence of their newborns. The mothers exhibited physical symptoms of fear.
When the newborns grew to maturity, they were again exposed to the odor of peppermint. Though these rats had never been shocked when exposed to this smell, their levels of stress hormones rose in its presence, indicating fear. This reaction is particularly notable given that their prior exposure to peppermint had been when they were too young to see or otherwise observe their environments.
“During the early days of an infant rat’s life,” Dr. Debiec said, “they are immune to learning information about environmental dangers. But if their mother is the source of threat information, we have shown they can learn from her and produce lasting memories.”
Although the study was conducted in rats, the researchers believe that a similar mechanism may explain how parents (including fathers, if they are regular caretakers) transmit some fear to their children, such as fear of the dentist or extreme shyness. Other studies have already shown that babies can be calmed by the scent of their mother; perhaps they can absorb her fear, as well.