Sleep Weakens Fear Memories, New Study Finds

Sharon Moore September 25, 2013

Scientists at Northwestern University Feinberg School of Medicine have found new evidence that fear memories can be reduced during sleep. Their findings could potentially enhance the effectiveness of exposure therapy by adding a night-time component to it.

For the first time, scientists have found that emotions could be manipulated during sleep. According to Katherina Hauner, a post-doctoral fellow at Northwestern University, their study shows a small yet significant reduction in fear during sleep. This opens up the possibility of enhancing phobia treatments through sleep intervention.

For the study, 15 healthy individuals received mild electric shocks whilst viewing two different faces, and at the same time, smelled a specific odorant. Subjects received different odorants to smell with each face, such as woody, clove, new sneaker, lemon or mint. After the task, they were asked to sleep.

While asleep, each of them received one of the two odorants they smelled during the experiment. The researchers released the odorants during slow wave sleep – the stage in which memory consolidation is thought to occur.

In the experiment, fear was measured using two indicators: small amounts of sweat in the skin, and neuroimaging with fMRI scan technique.

When the participants woke up, they were exposed to the same faces. But when they saw the face linked to the smell they have been exposed to during sleep, they showed less fear reaction than to the other face. Their brain scans also revealed changes in the patterns of brain activity in regions associated with emotion, such as the amygdala. These changes demonstrated a reduction in the reactivity that was specific to the targeted face image and linked to the odorant presented to the participants while they were asleep.

"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.

Their work was published in the journal Nature Neuroscience.

Source of this article:

Stimulus-specific enhancement of fear extinction during slow-wave sleep