The sense of smell seems to be behind a mother's ability to pass specific fears to her infant in the first days of life. Scientists believe fear can be passed between generations, with mother to child the primary route.
In a study of rats, scientists showed how a mother's alarm scent primed her days-old offspring to develop a peppermint phobia.
Jacek Debiec, a child and adolescent psychiatrist, began by teaching female rats to be scared of the smell of peppermint.
The rats were then mated and the minty smell released again, this time in the presence of the mothers and their newborn pups.
The findings may help mental health experts better understand how a mother's old traumas, including post-traumatic stress disorder and specific phobias, affect her children.
"It's more about increasing awareness that trauma may be passed to the second generation," said lead researcher Jacek Debiec from the University of Michigan Medical School in the US.
"It was really surprising to us that...it could be so early and could be so lasting," said 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.
Using special brain imaging, they zeroed in on a brain structure called the lateral amygdala as the key location for learning fears.
"This suggests," Debiec said, "that there may be ways to intervene to prevent children from learning irrational or harmful fear responses from their mothers, or reduce their impact."
The study appeared in the journal Proceedings of the National Academy of Sciences.
