Overcome fears by manipulating memory as you sleep
Whether it is snakes, flying or injections that give you the willies, it may one day be possible to simply snooze these fears away. A new study shows that fear memories can be manipulated while people sleep to be interpreted as less scary. The study is a step towards a less stressful alternative to exposure therapy, in which an individual must repeatedly confront their fear.
We know that sleep is important for processing memory. Every night, the events of the day are replayed in the sleeping brain to consolidate them as memories. Now Katherina Hauner at Northwestern University in Chicago and colleagues have shown that it is possible to target specific memories during this process and effectively overwrite them.
The team began by conditioning 15 people to feel fear. The volunteers were placed in an fMRI scanner and exposed to a series of neutral smells, such as lemon or mint. Each smell was paired with a photo of a face, and some of the pairings were also accompanied by a small electric shock.
Changes in the volunteers’ sweat levels, as measured by their skin-conductance response (SCR), and MRI scans of their amygdala - a region of the brain associated with fear - showed that they had learned to fear the faces and smells that were accompanied by the shock.
Once conditioned, the participants slept for 40 minutes outside of the scanner. During this time they were exposed to one of the smells they had been conditioned to fear earlier, but without the electric shock.
Again, the researchers measured changes in the SCR. Initially, the smell triggered a fear response. But the longer the smell was presented for, the more the fear response diminished.
When the subjects woke up, they were shown the same faces as before. The SCR and MRI measurements showed that the fear response to the face associated with the smell they had been exposed to during sleep was less pronounced than the fear response triggered by other faces.
A control group that had been similarly conditioned but then watched a movie instead of sleeping had no change in their fear responses.
To find out whether this was because the fear memory was replaced by something else during sleep or simply weakened, the team looked more closely at what was going on in the participants’ brains. They found that after sleep the MRI scans showed entirely different patterns of brain activity when they were shown the faces, rather than a weaker version of the same pattern seen during the conditioning state. “This supports the idea that it is new learning rather than unlearning,” says Hauner. “Maybe in future this could enhance daytime exposure therapy.”
But Hauner notes that more work is needed first. The fear response provoked by the electric shock is minor compared with that associated with most phobias or traumatic life events. The experiment also didn’t show whether the learned association had been banished for good.
Still, other researchers are positive about the work. “This is an exciting development in understanding the role of sleep in learning,” says Daniel Bendor at University College London. Some people may want a way of getting rid of unwanted memories, like the character who wants to forget his girlfriend in Eternal Sunshine of the Spotless Mind, he says. There are important clinical applications, too. “Extremely fearful experiences can lead to post-traumatic stress disorder, and this technique of cue-based extinction during sleep could eventually lead to a potential therapy,” he says.