Bolstering our sense of smell may reduce the risk of dementia

Whether it's the scent of clove-studded oranges or the fresh scent of a pine tree, the holidays are filled with aromas reminiscent of Christmases past. Now researchers say our sense of smell and its connection to our memory could be used to help fight dementia.

Our senses can deteriorate due to illness and old age. But while hearing or vision disorders quickly become apparent, a decline in our sense of smell can be insidious, taking months or even years to pass before it becomes clear.

“Although it can have other causes, losing your sense of smell can be an early sign of dementia,” says Dr Leah Mursaleen, head of research at Alzheimer's Research UK, adding that it is a potential indicator of damage in the brain. olfactory area of ​​the brain. brain – that is, the part of the brain responsible for smell.

That has led researchers to investigate whether loss of smell could be used to diagnose conditions like these Alzheimer's long before symptoms such as memory loss appear – an approach, experts say, that could give patients access to medicines such as lecanemab early in the course of the disease, when they work best to slow cognitive decline.

But just as research has suggested that using hearing aids could reduce the risk of developing dementia, questions are being asked about whether this is the case strengthening our sense of smell could do the same. Could a declining sense of smell be a risk factor for cognitive decline, and not just a symptom?

“Smell is closely involved in many brain processes, and especially in the emotional processing of stimuli,” says Prof. Thomas Hummel of the Dresden University of Technology. Smells, memories and emotions are often closely linked, and research reveals memories caused by smell are often rooted in our childhood.

“When olfactory function fails, stimuli lose their salience, which can affect general cognitive functions,” says Hummel.

Neurons involved in the olfactory system are also involved in other systems in the brain. Indeed, as Hummel and others note, some parts of the brain play a key role in cognitive and olfactory processes. As a result, cognitive processing can also be affected if the sense of smell becomes dysfunctional.

A colored transmission electron micrograph of a cross-section through olfactory receptors (cilia) projecting from an olfactory neuron (blue). This nerve cell is responsible for detecting smell. Photo: Science Photo Library/Steve Schmeissner/Getty Images

A number of studies have found that exposure to certain odors can boost or hinder cognition, while research by Hummel and colleagues shows that odor training can improve cognitive skills in the elderly. their verbal function and subjective well-being.

Even more relevant, a small study published last yearby researchers in Korea, revealed that intensive olfactory training led to improvements in depression, attention, memory and language functions in 34 patients with dementia, compared to 31 participants with dementia who had not received such training.

“We've seen some early research suggesting that 'training' our sense of smell, through repeated exposure to strong-smelling substances, could have benefits in improving cognitive performance on certain tasks,” says Mursaleen.

“However, much more research is needed to understand whether things like smell training can help prevent or slow the onset and progression of mild cognitive impairment and dementia.”

In addition to other problems, intensive scent training takes time and effort. In an attempt to solve this problem, Dr. Michael Leon, professor emeritus at the University of California, Irvine, and his team have devised a device called 'Memory Air' that releases forty different scents twice a night, while people sleep – an approach Leon says that “universal compliance” is possible. The hope is that exposing people to more scents, even while they sleep, could strengthen their sense of smell.

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The team is about to start a large trial of the gadget among older adults without dementia a smaller study that suggested the approach could improve memory performance in such participants. “We will then start a large trial with Alzheimer's patients who use that device,” says Leon.

In another small studyDr. Alex Bahar-Fuchs, a clinical neuropsychologist at Deakin University, Australia, investigates whether training cognitively healthy older adults to distinguish odors using an odor-matching memory game can help improve broader aspects of memory and cognition, compared with the use of a similar memory game. game based on matching images. The approach, he said, goes beyond passive exposure to odors by setting up cognitive tasks for participants.

“We believe that the neuroplastic properties of the brain's olfactory centers may make it more likely that improved performance in olfactory memory will generalize or transfer to memory functions more broadly,” he said.

Meanwhile, Prof. Victoria Tischler from the University of Surrey is trying to learn more about how our olfactory function changes as we normally age.

As part of their work, the team hopes to produce olfactory training kits suitable for healthy older people, people with mild cognitive impairment and people with dementia in care homes.

Tischler said it was important to cherish our most enigmatic feeling. “I would advise the public to look after their sense of smell, just as they look after other aspects of their sensory health,” such as their eyesight, she said.