A recent study out of Northwestern University suggests that presenting certain smells during sleep could help reduce fear memories.
Although the study showed the smell trigger attached to the fearful memory could help calm fears, scientists say it's too early to tell whether this could be used as a long-term treatment.
We talked to Dr. Jay Gottfried, the study's senior author and associate professor of neurology at Northwestern University Feinberg School of Medicine, to find out what the study means. Here is an edited version of our interview.
Q: What did the study involve?
A: We did sort of a Pavlovian response where we took a picture of a face and paired it with (a mild) electric shock so the face came to predict fear (for our patients). We did this with an odor in the background.
Afterward, we had the subjects take a nap, and every time they entered slow-wave sleep we presented that odor in the absence of that shock. By presenting that odor in sleep, we were able to reduce the emotional response evoked by the face. This is all done with the appropriate control.
We also did fear conditioning with a different face and a different smell but didn't present (that smell) in sleep. (Our subjects) still showed the same fear response (to the picture of the face where the smell wasn't presented during sleep).
Q: What was it about introducing the smell during sleep that made your test group less fearful to the picture when they woke up and saw it again?
A: What we think is happening is that when the smell is re-presented in sleep, it reactivates a memory of the fearful face, but of course in the absence of any shock. Therefore, after repeated presentations of the smell (in sleep), subjects form a new safe memory, such that the face no longer triggers a fear response. In the scientific literature, this is known as "fear extinction."
After subjects wake up, presentation of the face is now less fearful to the subjects (compared with a control condition involving a different face). We think areas of the brain including the hippocampus (for memory processing) and the amygdala (for emotion processing) are involved in mediating these changes.
Q: Why are the results of this study important?
A: It shows that we can actually modulate emotional memories in sleep.
Q: Practically speaking, how could this work?
A: That's the million-dollar question. Probably the next step is to find patients who have post-traumatic stress disorder. There is a pretty good subset of those patients who actually have smell triggers that will set off the anxiety and stress response. Gunpowder smells can set off a lot of those stress responses (for soldiers). Rape victims talk about how there's a certain smell or cologne may set off their anxiety.
There are many different kinds of circumstances where smell seems to play a role in trigger — if we could identify a given patients smell trigger we could try presenting that smell during sleep and see if we can achieve a kind of reduction in their reactive stress.
One aspect of our study we were looking at was the expression of fear within a couple of hours after sleep. If it works for a day and wears off, it's not much of a remedy. It would be interesting to see if through more exposure periods or some type of manipulation if this affects out into months.
Q: Can phobias affect sleep?
A: In general, people who are depressed or anxious have poorer sleep, so if the phobia is a very specific phobia, like arachnophobia (a fear of spiders), I don't know if that itself is going to cause much of a disruption of sleep. But with more generalized anxiety or phobic syndromes, there certainly could be sleep disruption.
Q: What types of treatments for phobias could arise out of this study?
A: I don't know if this would work as a treatment for anything (such as arachnophobia or other general phobias that aren't triggered by a smell). It worked in 15 young healthy adults. It could be cool looking into (treatments), but that would be more speculative.
Q: What type of phobias could be treated in a similar manner?
A: With our experiment, we basically taught and introduced new fear memories in the context of this odor. In the case of arachnophobia, for whatever reason these patients learn to be scared of spiders. In some distant memory they became scared of spiders, presumably in the absence of any smell. Simply presenting a smell in sleep if it has no bearing on the phobia may not have any impact.
What we could do is pair the spider with a certain smell in the daytime and then present the smell in sleep, but that's several steps beyond what we're studying.