In a new study Researchers from Northwestern Medicine tested the effects of gradual exposure therapy during Sleep. The therapy, which involves exposing people to things they Fear in small doses, has been previously shown to be effective at reducing fear responses.  However, it had never before been tested during sleep.

For the study, 15 healthy people were conditioned to develop a fear response to an image of a face. Every time researchers showed participants the image, they also administered a small electrical shock and exposed participants to a specific scent. Researchers then assessed participants’ fear responses by studying their perspiration levels and utilizing functional magnetic resonance imaging (MRI).

After these assessments, the researchers examined the participants as they slept, while re-exposing them to the same scent they had been conditioned to associate with fear. Researchers introduced the scent during slow wave sleep, the period of time during sleep when memory consolidation is thought to occur.

"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," study author Katherina Hauner, a postdoctoral fellow in neurology at Northwestern University’s Feinberg School of Medicine.

When the study participants woke up, they were exposed again to the image of the face that they had been conditioned to fear. However, their fear response was measurably lower compared to before they slept, according to researchers.

“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.