People’s memories of fearful events can be specifically diminished during sleep, reports a study published online this week in Nature Neuroscience. These findings add to our understanding of the types of learning that can occur during sleep, and may inform our efforts to treat fear disorders, such as post-traumatic stress disorder.
Katherina Hauner and colleagues trained participants to associate an odor with a mild electric shock.They found that individuals would experience a fear response, measured by the amount they sweat, when they smelled that odor later in the day. However, if people were exposed to the odor again, this time without the associated shock, while they napped, their fear response to the odor was reduced once they woke up even though they had no memory of experiencing the odor while they slept.Hauner and colleagues report that the activity pattern the odor elicited in the amygdala, a brain region known to participate in fear responses, was also altered by exposure to the odor during sleep.
Though previous studies have shown that new associative memories can be formed during sleep, this study shows that pre-existing memories can also be altered during sleep. Since such fear responses are involved in fear and anxiety disorders, the findings suggest that exposure therapy during sleep is a potential area for investigation in future clinical studies.