A new study published in the Proceedings of the National Academy of Sciences identifies how emotional trauma can be passed on to the next generation. Specifically, there is the potential for amygdala-dependent mother-to-infant transfer of a fear. This study aims to fill a gap in existing literature about how specific fears are transferred.

The researchers accept that emotional trauma is passed on from one generation to the next. For example, children witnessing their parent expressing fear to specific sounds or images begin to express fear to those cues. This can be an adaptive trait, learning to respond to social cues, but it can also be pathological fear.

According to the Los Angeles Times, odor is one of the cues of fear that passes on the fear. The researchers demonstrated this by conditioning non-pregnant female rats to fear the smell of peppermint by administering a mild electric shock to their feet while also exposing them to the peppermint odor. The rats later gave birth to litters of pups that were used in a variety of experiments along with their mothers, as well as other female rats that did not undergo fear conditioning.

While mothers normally offered comfort, the researchers found that when fear-conditioned mothers and their pups were exposed to the peppermint smell, cortisol levels rose in the pups. The young rats also developed an aversion to the odor when their mother wasn’t around, essentially moving away from the smell when they encountered it in a maze.