November 1, 2023
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Participants who sniffed odors while sleeping performed better on word memory tests
Smell is probably our most underrated sense. “If you ask people which meaning they would be most willing to give up, it would be the olfactory system” says Michael Leon, a neurobiologist at the University of California, Irvine. But the loss of smell has been linked to health complications such as depression and cognitive impairment. And there is growing evidence to show that olfactory training, which involves deliberately sniffing strong odors on a regular basis, can help prevent such deterioration. Now, a team of researchers led by Leon has managed to improve cognitive performance by exposing people to odors while they sleep. Twenty participants, all over 60 and generally healthy, received six months of overnight olfactory enrichment and all significantly improved their ability to remember word lists compared to a control group. The study appeared in Frontiers in neuroscience.
Scientists aren’t sure how nighttime odors may have produced this result, but Leon points out that neurons involved in smell have “direct highway access” to brain regions related to memory and emotions. In participants who received the treatment, the study authors observed physical changes in a brain structure that connects the memory and emotional centers, a pathway that often deteriorates as people age, especially those with Alzheimer’s disease.
Previous successful attempts to improve memory with odors generally depended on complicated interventions with multiple exposures a day. If overnight treatment proves successful in larger trials, it promises to be a less intrusive way to achieve similar effects, says Vidya Kamath, a neuropsychologist at Johns Hopkins University School of Medicine, who was not involved in the recent study.
Longer essays can also help answer some lingering questions. The new study used widely available essential oils, such as rose and eucalyptus, but researchers aren’t sure if any scent would get the same results. They don’t know to what extent the qualities of an odor (whether it is unpleasant or pleasant to people, for example) affect cognitive gains. It is also not clear to what extent the novelty influences it, says Micha&lstrok. Pieniak, a psychology researcher at the University of Wroclaw in Poland who has studied olfactory training.
Beyond stimulating the olfactory system, other interventions aimed at enriching people’s sensory environment (such as dance) have been associated with cognitive improvements in older people. Nighttime scents could be a strong line for further study, but Pieniak warns aromatherapy fans not to rush out and buy diffusers. The results are promising but “preliminary” and should be replicated with more participants, she says. León plans to conduct a larger study later this year, work that he hopes will remove any hint of doubt.