Researchers at Northwestern Medicine are working on a new type of therapy that could help people overcome phobias in their sleep. In an experiment, subjects conditioned to fear a certain stimulus exhibited reduced fear reactions after continuous nocturnal exposure. The findings represent the first time emotional memory has been manipulated in humans during sleep.

While gradual exposure therapy is nothing new, the additional nighttime component could help enhance and accelerate traditional fear treatment programs. Katherina Hauner, a postdoctoral fellow in neurology at Northwestern University Feinberg School of Medicine, said that although the observed decrease in fear was small, continuous exposure may eventually result in the complete erasure of the phobic memory.

"It's a novel finding," she said. "We showed a small but significant decrease in fear.”

In the study, which will be published Sep. 22 in the journal Nature Neuroscience, 15 healthy human subjects were enrolled in a controlled fear experiment. By administering mild electric shocks, researchers conditioned the subjects to fear a complex stimulus consisting of an odorant and an image of a face. Two different faces were used, and the smells ranged from mint and lemon to clove and woody. To assess the conditioned fear, the team relied on perspiration levels and functional magnetic resonance imaging (fMRI) scans.

When the subjects were asleep, the scientists partially reintroduced the phobic element by exposing them to the odorant. However, this time it was not accompanied by an electric shock. According to Hauner, the reintroduction took place during slow wave sleep, when memory consolidation is thought to take place.

"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 explained.

When the subjects woke up, they were once again exposed to the fear stimuli. When they saw the face whose smell they had been exposed to in their sleep, their fear reaction was comparatively lower.

“If it can be extended to pre-existing fear, the bigger picture is that, perhaps, the treatment of phobias can be enhanced during sleep," Hauner said.

Source: Hauner KK, Howard JD, Zelano C, Gottfried JA. Stimulus-specific enhancement of fear extinction during slow-wave sleep. Nature Neuroscience. 2013.