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.

A new study, published Jul. 28 in Proceedings of the National Academy of Sciences, sought to expand upon existing research to determine if scent had a role in fear transferal between mothers and newborns. Evidence of fear transferal over generations has been mounting since the second world war, when research began on Holocaust victims.

To test how this might occur, scientists focused on the sense of smell. They conditioned mother rats to fear the smell of peppermint by introducing the smell along with electric shocks prior to pregnancy. Then the pups were exposed to the peppermint smell and the activity measured in their lateral amygdala, where threats are detected and responses formulated in the brain.

Researchers found that even when the mother was not present, but the smell of her reacting to the peppermint was, the pups developed the same fear as their mother’s. When given a substance meant to prevent activity in the amygdala, the pups did not develop the phobia.

The results are of particular interest to scientists because the development of the fear occurs within the first few days of life and persists. In general, newborns are not able to retain memories of experiences without repeated exposure, often referred to as infantile amnesia. Yet, the pups retained the memory after single exposure.

Results from this study could prove useful to how treatment of trauma and PTSD are handled in the future. Therapeutic approaches that incorporate this new information could expand to include newborn children of people undergoing treatment. Substances to block amygdala activity could be used to prevent the transfer of phobias from mother to child.

Testing these fear reactions in humans is the next phase of research, according to the study. Determining how infants react to maternal fear responses in human subjects is important to establishing how treatment of phobias could evolve.