Mothers Share Their Fears With Newborns

In the animal kingdom, it has long been seen that even newborns know to fear certain predators or situations long before they could have possibly learned for themselves about that threat. This has baffled researchers for years, especially among those who scoff at the notion of intrinsic, or "pre-programmed," fears at birth. Now, a new study suggests that these initial fears are not intrinsic, but shared by their mother through odor alone.

According to a study published in the journal Proceedings of the National Academy of Sciences (PNAS), researchers were able to transfer a fear of peppermint from mothers to their newborn offspring in a controlled experiment.

They achieved this after teaching several female lab rats to fear the smell of spearmint by pairing the smell with mild electric shocks. Eventually, the rats learned to fear the smell alone, expecting a shock.

After giving birth, the children of these rats were found to fear the smell of peppermint too, but only after witnessing their mother grow weary in the wake of a peppermint odor.

"During the early days of an infant rat's life, they are immune to learning information about environmental dangers," study author Jacek Debiec said in a statement. "But if their mother is the source of threat information, we have shown they can learn from her and produce lasting memories."

But how exactly does this occur? According to the study, order is key. Not the odor of the peppermint mind you (although that was an important part of this experiment) but the odor of the rat pups' mother experiencing fear.

Like it is commonly said of sharks, wolves, and other intimidating animals, rats too can smell fear, at least among their own kind. Baby rats from a young age can at least learn that a threat is present simply from the odor of their fearful mother, which they will quickly learn to associate with that threat (in this case, peppermint).

Debiec next plans to apply these findings to what they know about fear circuitry in the brain, applying new knowledge to develop new ways to address and understand trauma, especially early childhood trauma, in humans.