Traumatic memories can be manipulated in sleeping mice to reduce their fearful responses during waking hours.  The finding, announced by  Stanford University researchers at the Society for Neuroscience meeting in New Orleans, Louisiana, suggests that sleep-based therapies could provide new options for treating conditions such as post-traumatic stress disorder (PTSD), Nature News Blog reports.

Currently, one of the most common treatments for PTSD requires the patient to recall the original trauma — an explosion, for example — in a psychiatrist’s office. With repeated “safe” exposures to the memory, patients may learn new associations that reduce the power of loud noises and other cues to trigger flashbacks.

Some patients are daunted by the task of intentionally recalling their traumatic memories. And many patients who undergo the therapy eventually relapse, says lead author Asya Rolls, perhaps because the technique becomes strongly associated with the psychiatrist’s office and does not generalize well to the outside world.

As an alternative to this approach, Rolls and her colleagues looked to emerging research that suggests sleep may be a unique new setting in which to manipulate memories.

In the study, they trained mice to fear the smell of jasmine by repeatedly pairing puffs of the chemical amyl acetate with weak electric shocks delivered to the mice’s feet. After 24 hours, the mice would freeze — a classic fear response — upon smelling the chemical alone.

Some mice received conventional exposure therapy, experiencing repeated odor puffs without ensuing electric shocks. These mice overcame their fear responses a day later, but relapsed when placed in a new cage — one not associated with the therapy.

In other mice, Rolls administered a drug to block protein production in the basolateral amygdala — a brain area associated with storage of fearful memories — just before the animals went to sleep. The researchers then exposed the sleeping mice to repeated odor puffs alone. Upon waking, these animals showed reduced fear responses to amyl acetate that carried over even into new environments.

Rolls points out that the protein synthesis drug would not be safe for use in humans, but that existing anti-anxiety medications could potentially have similar effects when paired with sleep-based exposure therapy. Future tests will be needed to uncover the cellular mechanisms of the treatment, but Rolls calls the work a successful proof of concept.

“The idea that you can actually erase memories during sleep, that you can manipulate them,” says Rolls. “It’s exciting.”