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Newborns can pick up on their mother's fear within the first few days of life, a new study reported. According to researchers from the University of Michigan Medical School and New York University, distressed mothers release an odor that babies can pick up. The odor can then teach babies to be fearful of the same things.

"Our research demonstrates that infants can learn from maternal expression of fear, very early in life. 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," stated lead investigator, Jacek Debiec, M.D., Ph.D., the U-M psychiatrist and neuroscientist.

For this study, the researchers first taught mother rats to be fearful of the smell of peppermint. The female rats were exposed to peppermint and mild but unpleasant electric shocks simultaneously prior to getting pregnant. The rats were then impregnated. After they gave birth, the researchers exposed them to the same minty smell but without the electric shock. Another group of female mice was used as the control group.

The team exposed the rats' offspring to peppermint with and without their mothers present. The researchers measured fear by using special brain imaging to analyze the lateral amygdala, which is a part of the brain that is linked to learning fears. The researchers found that the pups learned to fear peppermint odor when their fearful mothers were present and when they were not present.

"During the early days of an infant rat's life, 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," Debiec explained according to the press release.

The researchers hope that their study can help future research examine the effects that mothers with anxiety disorders have on their infants' fear development. The study was published in the journal, Proceedings of the National Academy of Sciences (PNAS).