Northwestern scientists have produced the first evidence that fear can be reduced during sleep.

Katherina Hauner, a postdoctoral fellow in neurology at the Feinberg School of Medicine, said the team of scientists was able to decrease fear felt by subjects regarding a specific memory by exposing them to that memory over and over while they slept. This is the first time emotional memory has been manipulated in humans during sleep.

“It’s a novel finding,” Hauner said in a news release. “We showed a small but significant decrease in fear. If it can be extended to pre-existing fear, the bigger picture is that, perhaps, the treatment of phobias can be enhanced during sleep.”

During the study, 15 healthy human participants were subjected to mild electric shocks as they saw two separate faces. A specific smell accompanied the viewing of each face, allowing both the face and smell to be associated with the fear of being shocked. Then, while subjects were asleep, one of the odors was re-presented in the absence of the associated faces and shocks.

“While this particular odorant was being presented during sleep, it was reactivating the memory of that face over and over again which is similar to the process of fear extinction during exposure therapy,” Hauner said in the release.

When the subjects woke up, they were again exposed to both faces. Neuroimaging and sweat analysis found subjects to have lower fear reactions to the face linked to the odor they had been exposed to during sleep.

Research for the study, published Sept. 23 in the journal Nature Neuroscience, was conducted in the lab of Feinberg Prof. Jay Gottfried, the study’s senior author. NU graduate student James D. Howard and NU postdoctoral researcher Christina Zelano also co-authored the study.

— Amy Whyte