“Sleep sort of stamps memories in more strongly,” said neurologist Jay Gottfried, senior author of the study, which was scheduled to be published online Sunday by the journal Nature Neuroscience. “That’s when a lot of memory formation can take place.”
The researchers first created a fear of a certain face in their subjects by using conditioning — making them link a face and an odor in their minds with a painful electric shock. After some trials, the participants became afraid of the face, and the smell acted as a cue associated with that face.
The researchers then used the smell to trigger fear memories during sleep as a way to enable patients to adjust without the stress of conscious terror.
Gottfried and his colleagues have not attempted this on preexisting fears, but theoretically it could be done — by creating a connection between a phobia and a distinct odor. He said the first type of patients who could be helped by this process would be those who already have an odor associated with their fear — for example, the smell of gunpowder.
“From a clinical perspective, this can be a new approach to try and treat stressful or traumatic memories,” Gottfried said.
He said that fear, a type of emotional memory, is often learned at a young age from experience or observation. A child who was bitten by a dog grows up afraid of dogs, but so does a child who sees his father attacked by one.
“Across all species, one thing is true: The learning of a fear occurs much more quickly than the fear extinction process,” said lead researcher and neurologist Katherina K. Hauner.
In exposure therapy, repeated exposure to the stimulus forms a new, safe memory.
For example, Hauner said, a fear of spiders can be quelled by the person initially looking at photos of spiders, then a real spider housed in a faraway cage, next by petting one with a thick glove, and finally by holding one.
“Extinction learning is typically known to be a new memory that essentially overwrites the fear memory,” said New York University’s Elizabeth Phelps, a psychologist and fear-conditioning researcher who was not involved in the study.
Hauner previously studied how slow and steady contact with spiders can change the brains of arachnophobes. As a postdoctoral researcher under olfactory expert Gottfried, she thought about using odors to trigger fear memories during sleep as a way to alter the emotional memory.
The researchers showed 15 healthy subjects a photo of a different face every few seconds, but for two faces they received foot electric shocks. They eventually learned to fear both faces, as measured by increased levels of sweat.