Scientists at Northwestern University say they have lowered levels of
fear in people by using certain odors to trigger and rechannel
frightening memories into harmless ones during deep sleep.
Researchers created an artificial "fear" in 15 healthy subjects by showing them photos of different faces and applying electric shocks when two of the photos were shown. Conditioning also included associating each face with a particular odor.
Fear was detected through a process similar to a lie detector test, which measured small amounts of sweat in the
skin. After several trials the participants
became afraid of the face and the smell associated with it; the scent was
then used to trigger "fear memories" during deep sleep in order to
allow patients to avoid the stress of conscious terror.
The subjects then napped for a couple of hours. Whenever they
fell into a deep phase known as slow-wave sleep, they were given the odor associated with one of the two "scary" faces, but without the accompanying jolts.
The subjects were allowed to stay in slow-wave sleep for periods ranging from five to 40 minutes: the effect was strongest for those who slept for longest.
After the subjects awoke, they again went through the process of
being shown the series of different faces. This time they weren’t as
afraid of the face with the scent they had been exposed to during sleep, however they remained fearful
of the other, whose associated odor they hadn’t been exposed to during
sleep.
Also, those who were exposed to the scent for the longest total time
while sleeping were less afraid of the face than those who had smelled it for a short time.
The subjects did not know what happened during their sleep.
Researchers also used fMRI
(functional magnetic resonance imaging). The fMRI results showed
changes in regions associated with memory, such as the hippocampus, and
changes in patterns of brain activity in regions associated with
emotion, such as the amygdala. These brain changes reflected a decrease
in reactivity that was specific to the targeted face image associated
with the scent presented during sleep.
Sleep plays a key role in memory consolidation, which involves parts of
the brain replaying the events of the day and choosing which parts to
store for safekeeping and which to forgo.
Dr. Jay Gottfried, PhD., senior author of the study, says "Sleep sort of stamps memories in more strongly: that’s when a lot of memory formation can take place.”
People with phobias are already commonly treated with "gradual
exposure" therapy while they are awake, where they are exposed to the
thing they are frightened of in incremental degrees. This study suggests that the theory could be extended to therapy while they are in slow-wave, or deep, sleep.
"It's a novel finding," said Katherina Hauner, a postdoctoral fellow in
neurology at Northwestern University Feinberg School of Medicine. "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."
The study was published in the Sept. 22 journal Nature Neuroscience.
References:
washingtonpost.com
sciencedaily.com
bbc.co.uk
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