Babies can get new phobias just by smelling the odor of their distressed mothers.
A new study by the University of Michigan Medical School and New York University School of Medicine showed mother rats can teach new fears to their young (2).
The concept that factors other than DNA can be inherited was documented in people and plants in the past, but the method by which such a feat was possible was not known. This concept, called epigenetic inheritance, involves the inheritance of parent’s experiences can be inherited as well as their DNA through certain epigenetic tags. However, the proposal of odor as the cause of epigenetic inheritance has been proposed before. In November 1, 2013, a different research paper by the Emory University School of Medicine proposed that parental fears experienced by male mice could be transmitted to young mice through the odor of chemicals bound to the sperm of the male mice (3).
In the first few days after rats are born, they can be made to fear certain stimuli if they are subjected to an odor their mother releases, characteristic of when the mother experiences fear (2).
In the study conducted by Jacek Debiec, female rats were made to fear the smell of peppermint through conditioning before pregnant with baby rats. After the female rats gave birth, the team exposed the mothers to the peppermint smell again and placed baby rats in a separate container which allowed for only olfactory stimuli from the mothers to enter. After discovering the baby rats showed increased levels of cortisol, a neurotransmitter associated with fear, to the peppermint smell both immediately after being exposed to their mother’s odor and the peppermint smell and 1 week after, the researchers concluded the mothers released an odor provoking fear in their young, suggesting the fear lasts for a long time. This contrasts with the fears that the young rats experience themselves, which can fade almost instantly and not be retained for a week without constant repetition of the stimulus causing the fear (2).
“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,” says Debiec (1).
The brain structure responsible for the elevation of cortisol was also found. Using special brain imaging with a compound called 2-DG as an optical imaging agent for fluorescence, the researchers localized the neural location for learning fears to be at the amygdala (2). The amygdala are considered part of the limbic system, and is known to be responsible for emotional reactions like fear. Several studies have found that anxiety and stress disorders result from abnormal physiology of the amygdala.
Debiec hopes that this research can be used to help human patients with phobias or anxiety disorders and understand the mechanism of epigenetic inheritance, especially as the role of a mother’s scent in calming human babies has been shown (1).
1. Gavin, Kara, Learning the smell of fear: Mothers teach babies their own fears via odor, U-M research finds (2014). Available at http://www.uofmhealth.org/news/archive/201407/learning-smell-fear-mothers-teach-babies-their-own-fears
2. Debiec, Jacek, Intergenerational transmission of emotional trauma through amygdala-dependent mother-to-infant transfer of specific fear (2014). Available at http://www.pnas.org/content/early/2014/07/23/1316740111.full.pdf+html
3. Dias, Brian G, Parental olfactory experience influences behavior and neural structure in subsequent generations (2013). http://www.nature.com/neuro/journal/v17/n1/full/nn.3594.html