By introducing scents into one nostril of sleeping subjects, scientists could improve their memory retention capability. The findings of the study could one day help restore memory capabilities in patients with brain injuries, or treat people with post-traumatic stress disorder (PTSD) where memory often triggers their PTSD.
Memory Consolidation During Sleep
Scientists know that when people sleep, a kind of memory consolidation process occurs. The part of the brain called the hippocampus holds the memories, acting sort of like a short-term buffer. During sleep, these memories are transferred to the neocortex and consolidated as long term memories. How this process occurs is unknown to scientists.
In this study, the researchers were able to trigger this process in one side of the brain. They then compared the two hemispheres of the brain to isolate the specific activity that corresponds to memory reactivation.
Memories Associated With Location Stored Differently
Another thing researchers know is that memories associated with location is stored in different hemispheres of the brain. For example, if we memorize something associated being on our left side, that memory is stored in the right brain hemisphere. The opposite is true if we memorize something associated with being on our right side. That memory will be stored in the left brain hemisphere.
In this study, participants were asked to remember the location of words presented on either the left or right side of a computer screen while they were exposed to the scent of a rose. They were then tested to see how they had memorized the words. Afterwards, they took a nap. During the nap, they were again exposed to the scent of the rose but only in one nostril. The electrical brain activity of the participants was also measured during sleep.
Better Memory After Smelling a Rose in One Nostril
What the researchers found is that the brainwaves of the hemisphere that received the scent showed better electrical signatures of memory consolidation during sleep.
The significant finding was during the testing of the participants when they awoke. They underwent a second memory test for the words they memorized before taking their nap. The participants recalled the words significantly better for the words presented on the side affected by smell than the memory for words presented on the other side.
The researchers’ technique may also have clinical applications. When PTSD patients recall a trauma, there is usually more activity is the right brain hemisphere where emotions are associated. This technique might be potentially adapted to be able to affect the traumatic memories during sleep and reduce the emotional stress of the patients. This method could also be developed to assist in rehabilitation therapy after one-sided brain damage due to stroke in patients.
“Our findings emphasize that the memory consolidation process can be amplified by external cues such as scents,” said the lead author Ella Bar in their press release.
“By using the special organization of the olfactory pathways, memories can be manipulated in a local manner on one side of the brain. Our finding demonstrates that memory consolidation likely involves a nocturnal ‘dialogue’ between the hippocampus and specific regions in the cerebral cortex,” she said.