NEW ORLEANS — Fearful associations can be knocked back during sleep, research in mice shows. After receiving an injection of a drug, a nasty link between a scent and a painful foot shock faded as the mice slumbered.
The results are preliminary but may ultimately show how to get around a roadblock in treatments for people with post-traumatic stress disorder: Traumatic associations can be weakened in a doctor’s office, but those memories can flood back when triggered by specific events in everyday life. The new finding suggests that the hazy world of sleep, lacking any particular real-world context, might be a better place to diminish such memories.
Neuroscientist Asya Rolls of Stanford University and colleagues taught mice that when they smelled jasmine, a foot shock was not far behind. A day later, as the mice slept, the researchers wafted the smell over the animals, strengthening and solidifying the scary link between jasmine and pain. A day after that, the mice froze in fear when they caught a whiff of jasmine, even though the animals were in an entirely new room unassociated with the original shock.
But Rolls and her team could interrupt this sleep-strengthening process with the antibiotic anisomycin, injected into the amygdala—a brain structure involved in memory storage. Before the mice were exposed to jasmine during sleep, the researchers injected some of them with the drug. The next day, these mice didn’t freeze as much as the mice that didn’t get the drug. The results suggest that during sleep, traumatic memories, such as the kind that plague people with PTSD, can be effectively weakened.
During sleep, the mind is not rooted in any particular environment. So the effect of curbing traumatic memories in someone who is fast asleep wouldn’t be linked to any specific setting, such as a doctor’s office. This could protect a person from re-experiencing the trauma in other situations, Rolls said in a briefing October 16 at the annual meeting of the Society for Neuroscience.
What’s more, because sleep is a brain state outside of conscious control, it may offer access to memories that are locked up tight during waking hours, Rolls said. And reactivating traumatic memories during sleep may be less painful for people, sparing them the difficulty of reliving a traumatic experience while awake.
Recently, Rebecca Spencer of the University of Massachusetts Amherst and colleagues found that people’s fearful memories get strengthened during sleep (SN: 2/25/12, p. 8), work that implied that keeping someone awake could prevent the formation of unpleasant memories. The new study “puts an interesting twist on our work,” she says. Instead of losing sleep, people could lose the fear memory and still get a good night’s sleep.
It’s too early to say how such an intervention would work in people. The drug used in the study was chosen because it targets protein production in cells, a process that strengthens memory during sleep. But the drug has side effects, and it wouldn’t be reasonable to inject it into people’s brains, said Rolls. Still, there might be other safe ways to destroy harmful memories during sleep in people, she says. “I think this has huge potential.”