New research shows that it is possible to reduce fear by exposing the brain to cues that trigger a fear response, while sleeping. Most long-term memories get consolidated during sleep. This is the first research that demonstrates that an emotional memory can be altered during sleep.

The study, conducted by researchers at the Northwestern University Feinberg School of Medicine, reduced fear in a group of test participants by exposing them to certain odors that are linked with a fear.

"It's a novel finding. 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," said Katherina Hauner, a postdoctoral fellow in neurology at Northwestern University Feinberg School of Medicine.

There are several kinds of phobias; some mild while others are severe enough to interfere in daily life. In the study, researchers created fear in people's minds by conditioning them to a certain image.

The study included 15 people who were shown images of two faces. Researchers gave them a mild electric shock when they looked at a particular image. The shocks were accompanied with a particular smell. After a while, participants began showing fear in response to the image and the associated odor.

Their fear was measured using two ways; one was by detecting sweat in the skin while the other was using a functional magnetic resonance imaging fMRI. The scans showed specific changes in regions of the brain associated with fear.

The odors were re-presented to each individual during sleep. The respondents were asleep for about 40 minutes. The brain consolidates memories during sleep. So, presence of the odor triggered the brain to react with fear.

Brain scans of the respondents showed that the Hippocampus region (area linked to memory) and the Amygdala region (area linked with emotion) showed changes in patterns when the odor was introduced during sleep.

The participants were showed the image again after they woke up. This time, it was observed that their level of fear was lower than before. The effect was the highest in people who had slept the longest.

"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 a news release.

The scientists therefore concluded that multiple sessions of the therapy could heal a phobia completely.

 "Many people who have survived traumatic events, such as fires or road traffic accidents, have a physiological fear response to triggers of their memories. Triggers often include smells, such as smoke, petrol, antiseptic smells and alcohol. Infusing these smells during periods of slow-wave sleep could help to extinguish the fear response," Jennifer Wild, consultant clinical psychologist at the King's College London Institute of Psychiatry said to BBC.

Researchers haven't conducted the experiment on people who already suffer from a phobia, but they are quite optimistic that associating an odor to a phobia could help reduce its intensity, The Washington Post reported.

The study is published in the journal Nature Neuroscience.