Researchers testing rats and their newborn pups showed the babies can adapt the specific fears of their mothers in the earliest days of life by picking up on the scent they emit while in emotional distress.
Scientists from New York University and University of Michigan studied mother rats who learned to fear the smell of peppermint through lab conditioning before they became pregnant.
After the rats gave birth, researchers exposed the mothers to a minty scent to trigger the fear response. Using a comparison group of female rats without a fear of peppermint, researchers then exposed the rat pups of both groups of mothers to the peppermint scent.
After analyzing brain images as well as genetic activity in brain cells and cortisol in the blood, the scientists honed in on the “lateral amygdala” as the area of the brain where fears are learned, and found elevated activity in the pups.
While the scientists say it’s too soon to know if same effect occurs between human mothers and babies, the research builds on previous work looking at how fear operates in the brain. Prior work in this specialized area has led to new treatments for human patients with anxiety, phobias and other fear disorders, the scientists say.
The team found that not only could the learned fears in the baby rats be long-lasting, but the newborns could even learn the fears without their mothers present.
“Maternal presence was not needed for fear transmission, because an elevation of pups’ corticosterone induced by odor of the frightened mother along with a novel peppermint odor was sufficient to produce pups’ subsequent aversion to that odor,” the researchers said in a paper published Monday in the journal “Proceedings of the National Academy of Science of the United States of America. ”
Jacek Debiec, one of the neuroscientists that led the research, said in a statement that during the early days of an infant rat’s life, they are immune to learning 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,” he said.
“Before they can even make their own experiences, they basically acquire their mothers’ experiences,” he said. “Most importantly, these maternally-transmitted memories are long-lived whereas other types of infant learning, if not repeated, rapidly perish.”
The positive news is when the baby rats were given a substance that blocked activity in the amygdala, the pups did not learn the fear of peppermint, suggesting there are possible interventions to prevent human children from picking up on “irrational or harmful fear responses,” passed on from their mothers.
