New research suggests that exposing older adults to certain pleasant smells during the night can lead to positive effects on their brain health. This process, called “olfactory enrichment,” was associated with significant improvements in memory and learning. It also appeared to influence the connections of this brain pathway that plays an important role in memory and decision-making. The findings have been published in Frontiers in Neuroscience.
Cognitive decline, which refers to the deterioration of cognitive functions such as memory and reasoning, is becoming a significant issue among older adults. This decline can have profound impacts on both individuals and society as a whole. Individuals experience challenges in their daily lives, while society faces increased healthcare and caregiving demands. In response to this growing concern, the researchers aimed to develop a treatment strategy that could effectively counteract or slow down cognitive decline in older adults.
Environmental enrichment is a concept that has been studied extensively in animal research. It involves enhancing the environment with various stimulating factors, such as social interactions, physical activities, and sensory experiences. In animal studies, environmental enrichment has shown to positively impact brain structure and function, particularly in relation to cognitive abilities. The researchers aimed to take this concept of environmental enrichment, which had been successful in animal studies, and adapt it for use in older adults. In this case, they chose to focus on olfactory stimulation as a form of sensory enrichment.
The olfactory system, responsible for the sense of smell, has a unique anatomical feature: it has direct connections to the limbic system in the brain. The limbic system plays a crucial role in memory and emotion. This direct connection suggests that sensory experiences related to smell might directly influence the regions of the brain responsible for memory and emotional processing.
Given the intricate link between olfaction and the limbic system, the researchers speculated that stimulating the olfactory system could potentially lead to positive effects on memory-related brain areas, potentially improving cognitive function in older adults.
“We had developed an effective treatment for autism using an environmental enrichment approach, based on hundred of lab animal studies,” explained study author Michael Leon, a professor of neurobiology and behavior at the University of California, Irvine and a member of the Institute for Memory Impairments and Neurological Disorders. “The therapy depends on extra sensory stimulation. We thought that we could use a similar approach to treat memory loss in aging, but using olfactory enrichment alone, as had been shown in a lab animal study.”
For their study, the researchers recruited a sample of 43 older adults (ages 60–85) with no cognitive impairment or dementia. The participants were randomly assigned to two groups: the olfactory enrichment group and the control group. The olfactory enrichment group received an odor diffuser with seven different essential oil odorants. They were instructed to use the diffuser at night, rotating through the odorants over the course of 6 months. The control group also used an odor diffuser but with distilled water containing trace amounts of odorant.
Participants underwent cognitive assessments, olfactory tests, and mental health evaluations at the beginning of the study and after 6 months. Cognitive assessments included tasks to evaluate memory, working memory, attention, and other cognitive functions. Olfactory tests measured the participants’ olfactory identification, discrimination, and threshold abilities.
MRI scans were conducted on participants to assess brain changes associated with olfactory enrichment. Diffusion-weighted imaging (DWI) was used to examine white matter pathways relevant to olfaction and memory, such as the uncinate fasciculus and the hippocampal cingulum.
The findings indicated significant improvements in verbal learning and memory performance among enriched participants compared to controls. The improvement was particularly evident in the Rey Auditory Verbal Learning Test (RAVLT), which assesses verbal learning and memory. The enriched group showed a significant 226% difference in performance compared to controls on the last learning trial.
“Too little older stimulation causes the memory centers of the brain to deteriorate,” Leon told PsyPost. “Both olfaction and memory begin to decline after the age of 60. Extra odor stimulation improves memory in older adults.”
Furthermore, the study found changes in the mean diffusivity of the left uncinate fasciculus. The uncinate fasciculus is a specific pathway that connects two important areas of the brain: the amygdala and the prefrontal cortex. The amygdala is involved in processing emotions, while the prefrontal cortex is responsible for decision-making and other complex thinking tasks.
The changes in mean diffusivity suggest that olfactory enrichment had positive effects on neural pathways associated with memory and socio-emotional processing. This aligns with prior research showing that enrichment interventions can influence white matter diffusivity.
“We were surprised at how closely aligned the changes in memory and the brain were,” Leon said.
The study suggests that even minimal olfactory enrichment during sleep can effectively improve cognition and neural function, making it a potentially valuable and cost-effective approach, even for individuals with dementia. But the study only included a relatively small number of participants, which might not be representative of the entire population of older adults. In addition, the design of the study’s diffusion device allowed for the exposure to only one type of odorant each night.
“We need to replicate the findings with a larger number of people and with a larger number of odors,” Leon explained.
“As few people will give themselves 40 odors 2X each day, what seems to be optimal, we’ve designed a device that puts out that pattern of odor stimuli as you sleep, so no effort is involved in getting the stimulation that your brain needs,” he added. “Those interested in obtaining access to this device can sign up at www.memoryair.com.”
The study, “Overnight olfactory enrichment using an odorant diffuser improves memory and modifies the uncinate fasciculus in older adults“, was authored by Cynthia C. Woo, Blake Miranda, Mithra Sathishkumar, Farideh Dehkordi-Vakil, Michael A. Yassa, and Michael Leon.
