Sleep helps eliminate fear.
We can reset our brains and calm our emotions by sleeping. Perhaps it can do more, though: if sleepers are exposed to odors they associate with bad memories, it appears they can lose the fear those memories bring.
Previous studies have shown that sleep helps eliminate fear in general. But whether it is possible to focus this effect through the careful use of odours has not been tested in humans.
Katherina Hauner and Jay Gottfried of Northwestern University in Evanston, Illinois, exposed subjects to four pictures of faces and a series of inoffensive smells such as mint. When one of the faces appeared, the volunteers got a painful electric shock.
Afterwards, the researchers measured the amount of electricity conducted by the subjects’ skin – a measure that goes up when afraid, because the sweat produced is a good conductor. The researchers found that conductance spiked whenever the volunteers saw the face associated with the shock.
They then let half the subjects sleep, and exposed this group to variable amounts of the odour that had been presented along with the “painful” face. The next day, these volunteers were much less afraid of the face – and those with the least fear were those that had received the highest exposure to the odour while asleep. Brain scans also showed that brain areas associated with fear and with memory were less active after this exposure.
The other group of subjects stayed awake while they received pulses of the odour associated with the “painful” face. Unlike the sleeping group, however, these volunteers became more afraid of the face with greater exposure to the odour.
The question now is why sleep dissociates the fear from the image, rather than reinforcing the connection. Hauner says a clue may lie in reports from the awake volunteers, who said they saw the face in their minds every time they smelled the odour.
The technique could eventually enhance treatments for posttraumatic stress disorder by associating images from the traumatic memory with a smell, and then using odour exposure while sleeping, says Hauner. The next step is to study whether the effect occurs during REM sleep or slow-wave sleep.
Via New Scientist