From around 1950 and onward, a new trouble arose in Poland; children of Holocaust survivors were experiencing nightmares and flashbacks of events they had never undergone and were acquiring the avoidance instincts of their parents. No genetic cause could be found for the behavior, until now. A new study from the University of Michigan Medical School and New York University reveals that the odor of a distressed mother can teach infants to acquire fears, even if they are only a few days old.

The study is the first direct observation of this kind of fear transmission. It helps to explain how a mother's traumatic experience can affect her children's mental health in profound ways. With this new information, mental health experts can also explain the need for expectant mothers to seek professional help during and after pregnancy.

More About the Study

Researchers used rats to examine fear transmission. They began by teaching non-pregnant female rats to fear the smell of peppermint by exposing them to mild electric shocks when the smell was detected. After pregnancy and birth, the baby rats were exposed to the smell of peppermint with their mothers in the same compartment, with their mothers in a compartment attached by a pipe, and without their mothers present. Reactions were measured through brain imaging and cortisol levels in the blood.

If the mother rats expressed a specific fear when her pups were present, the newborns could learn their mother's fear. This does not come as a surprise. What is surprising is that even when the mother of the rat was not physically present with the pups, the pups could still learn the fear. The smell of their mother's fearful response alone was enough for baby rats to learn the fear.

Through neuroimaging, researchers traced this reaction to a part of the brain called the lateral amygdala, an area that is key to detecting and responding to threats. When researchers gave the pups a substance to block activity in the amygdala, they did not learn the fear.

How Will This Affect Anxiety Treatment in Parents and Children?

This study emphasizes the importance of anxiety treatment for mothers before, during, and after pregnancy. Just as children of Holocaust survivors could learn the fears of their parents, so children of mothers with anxiety can also acquire their mothers' fears. If you or someone you know has anxiety and is pregnant or considering becoming pregnant, talk to a mental health professional. Confronting your anxieties before a child is born is essential for your child to have a happy and anxiety-free life.

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Jacek Debiec, Regina Marie Sullivan. Intergenerational transmission of emotional trauma through amygdala-dependent mother-to-infant transfer of specific fear. Proceedings of the National Academy of Sciences of the United States of America, 2014; DOI: 10.1073/pnas.1316740111

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