The study led by Ella Bar explained the process saying, “We know that a memory consolidation process takes place in the brain during sleep. For long-term memory storage, information gradually transitions from the hippocampus — a brain region that serves as a temporary buffer for new memories — to the neocortex. But how this transition happens remains an unsolved mystery.”
“By triggering consolidation processes in only one side of the brain during sleep, we were able to compare the activity between the hemispheres and isolate the specific activity that corresponds to memory reactivation,” adds Prof. Yuval Nir of TAU’s Sackler Faculty of Medicine and Sagol School of Neuroscience.
Memory Recall
The study took from the knowledge that memories associated with location on the left side of a patient are mostly stored in the right brain hemisphere and vice versa. While exposed to the scent of a rose, participants were asked to remember the location of words presented on either the left or right side of a computer screen. They were then tested on their memory of the word locations. Participants were then required to nap as the scent of roses was administered again, but only to one nostril.
The research team also recorded electrical brain activity during sleep with EEG. It was shown that the “one sided” rose scent delivery led to different sleep waves in the two hemispheres. The side that received the scent showed better electrical signatures of memory consolidation during sleep. After participants woke, they underwent a second memory test, which included recalling the words they had been exposed to before falling asleep.
It was found that with this “one-sided” odor delivery, the researchers were able to reactivate and boost specific memories that were stored in a specific brain hemisphere.
“The memory of the subjects was significantly better for words presented on the side affected by smell than the memory for words presented on the other side,” Bar says.
“Our findings emphasize that the memory consolidation process can be amplified by external cues such as scents,” she concludes. “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.”
Researchers hope that this method may have clinical applications in the future. The technique could potentially influence the aspect of memory during sleep which could help to decrease emotional stress that accompanies recall of traumatic memory. This could offer alternative treatments for patients with brain injury or post-traumatic stress disorder (PTSD) patients who show higher activity in the right hemisphere when recalling a trauma. Additionally, researchers believe this method could also be used to further develop rehabilitation therapy after one-sided brain damage due to stoke.