New sleep method strengthens memory retention

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A new method bolsters memory processes in the brain during sleep, according to a new joint study by researchers from Tel Aviv University and the Weizmann Institute of Science in Israel and published in the journal Current Biology.

The method relies on a memory-evoking scent administered to one nostril. It helps researchers understand how sleep aids memory, and in the future could possibly help to restore memory capabilities following brain injuries or help treat people with post-traumatic stress disorder (PTSD) for whom memory often serves as a trigger, the researchers said.

For the study, researchers led by Ella Bar, a PhD student at the university, began from the knowledge that memories associated with locations on the left side of a person are mostly stored in the right brain hemisphere and vice versa. While exposed to the scent of a rose, research participants were asked to remember the location of words presented on either the left or right side of a computer screen. Participants were then tested on their memory of the word locations, then proceeded to nap at the lab. As the participants were napping, the scent of roses was administered again, but this time to only one nostril.

Memory consolidation processes take place during sleep, Bar said. For long-term memory storage, information gradually transitions from the hippocampus, which serves as a temporary buffer for new memories, to the neocortex. By triggering consolidation processes in one side of the brain during sleep, the researchers could compare activity between the hemispheres and isolate specific activity that corresponds to memory reactivation.

With the one-sided delivery, the researchers were able to reactivate and boost specific memories that were stored in a specific brain hemisphere, according to the study.

The team also recorded electrical brain activity during sleep with electroencephalogram (EEG). The results showed that the one-sided rose scent delivery led to different sleep waves in the two hemispheres. The hemisphere that received the scent revealed better electrical signatures of memory consolidation during sleep. Finally, subjects were asked after waking up to undergo a second memory test about the words they had been exposed to before falling asleep.

“Our findings emphasize that the memory consolidation process can be amplified by external cues such as scents,” said Bar in a statement. “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.”