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The Smell of Fear and Inherited Trauma

Posted By Prucia Buscell, Thursday, July 31, 2014
Updated: Friday, August 01, 2014

Babies can learn very early in life to fear something that frightened their mothers even before they were born. Scientists have known for some time that trauma can ripple through generations. New research on fear transmission may help explain how that happens.

A team of researchers from the University of Michigan Medical School taught a group of female rats to fear the smell of peppermint by repeatedly accompanying the smell with mild but unpleasant electric shocks. That was before they were pregnant. After the rats became pregnant and gave birth, the team exposed them to the peppermint smell again, without the shocks, to induce the fear response again.

A story on the university website by Kara Gavin explains that the babies of fearful mother rats, and a comparable group of rat pups whose mothers had no fear of peppermint, were exposed to the smell under many conditions with and without their mothers. When babies were separated from their mothers and exposed to the minty smell along with air piped to them from a nearby container occupied by their frightened mothers, they quickly learned to fear the smell. The trigger for learning apparently was the scent the mothers give off when they are fearful.

"Our research demonstrates that infants can learn from maternal expression of fear very early in life," said Jacek Debiec, MD, PhD, the psychiatrist and neuroscientist who led the research. "Before they can even make their own experiences, they basically acquire their mothers' experiences. Most important, these maternally transmitted memories are long-lived, where other types of infant learning, if not repeated, rapidly perish."

In a paper published in Proceedings of the National Academy of Science, Debiec and colleague Regina Marie Sullivan PhD, describe how brain imaging, studies of the genetic activity of individual brain cells, and monitoring blood levels of cortisol, the stress hormone, were used to examine the working of fear in the brain. They found a brain structure called the lateral amygdale was the key location for learning fears, and when they gave baby rats something that blocked activity in that region, they did not learn their mothers' fear. That could help explain why some offspring of traumatized mothers don't inherit fears. The authors hope the work will aid understanding of post-traumatic stress and other mental ills in humans.

Debiec, recalls working with adult children of Holocaust survivors who had nightmares and flashbacks related to experiences they had not endured themselves. Rachel Yehuda, a psychiatrist at Mount Sinai Hospital in New York, has studied descendants of Holocaust survivors and the children of women who were pregnant and in or near the World Trade Center on 9/11/2001. She found evidence of intergenerational trauma transmission that could not have occurred through storytelling. She was not involved in Debiec's work, but she told Arielle Duhaime-Ross of Verge magazine that the study is valuable because it provides molecular analysis that would not be possible in living human brains. She said understanding the brain changes that occur with intergenerational transmission could help people understand the long-term impact of parental experiences. "Your fears are not only a response to your personal experiences," Yehuda told Verge, "but those that your parents had as well."

Tags:  buscell  complexity matters  research  resilience 

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