Older people improved their memory by being exposed to smells at night

It sounds almost unbelievable.

A small device that released odours into the bedroom for two hours every night for six months was all it took.

The healthy older adults who were exposed to these smells performed three times better on cognitive tests than before the experiment.

Early signs of Alzheimer's

But the idea that smells can improve memory is not surprising to everyone.

“The findings are quite sensational, but the fact that the sense of smell is linked to dementia is not new,” Geir Selbæk tells sciencenorway.no. He is head of research at the Norwegian National Centre for Ageing and Health.

Loss of sense of smell can indeed be an early sign of Alzheimer's.

Few participants

At the same time, there is reason to be cautious of this study, according to Selbæk.

The experiment had few participants with just over 20 in each group. One group was given a device that emitted scents from essential oils.

This is a type of oil found in most plants. Lemon oil and jasmine oil are among the most well-known. They are extracted from the plants by pressing, distillation, or other processes. Essential oils are volatile, meaning they evaporate easily.

The control group was given a placebo device that only emitted very diluted odours.

The already small experiment became even smaller due to Covid-19. Researchers had to cancel some of the cognitive tests.

That means that the results relating to memory are based on just over 10 people in each group.

Nevertheless, the findings are so exciting that they are worth researching further, Selbæk says.

Can odours strengthen the brain?

What is actually the cause and effect in the relationship between the sense of smell and dementia?

Is it dementia that leads to loss of smell? Or is it the opposite? In other words, that a poor sense of smell simply increases the risk of dementia.

If so, it makes sense that training sense of smell can make the brain more robust. Or as in this new study, give people better memory.

The senses may be important

In that case, there is a possible explanation, according to Selbæk.

“The idea is that the nerve that conveys the sense of smell is almost like a highway to parts of the brain that are important not only for cognitive functions like memory, but also for the emotional,” Selbæk says.

Just think about how strong memories certain smells can evoke.

Sight, smell, and hearing

The new finding fits into a range of studies that point to the same thing.

Namely, that our senses are important for keeping the brain healthy.

So it's not just exercising the brain that is important as you get older, but perhaps also sight, smell, and hearing.

For example, people with poor hearing are more likely to develop dementia, but hearing aids seem to nullify the risk.

Seven different essential oils

This new experiment took place at night.

Olfactory training usually occurs when awake.

Those who have lost their sense of smell after Covid-19 can retrain it with the help of essential oils. Part of the treatment involves trying to visualise, for example, lavender or orange while smelling the oils.

The researchers behind the new study also used seven different essential oils in the diffusion device, one for each night of the week. But the participants were not told about this.

Perhaps the smell does not need to be interpreted

So how can a smell improve our memory when we are not consciously aware of it?

“It’s not certain that the impression has be interpreted,” Selbæk says.

Perhaps the brain is stimulated regardless. And that in itself is enough to strengthen the brain. But so far, we cannot confirm that it works this way.

Selbæk hopes the researchers behind the idea will expand the experiment.

“There should be more participants, and the results should be observed over a longer period,” the Norwegian researcher says.

———

Translated by Alette Bjordal Gjellesvik.

Read the Norwegian version of this article on forskning.no

Reference:

Woo et al. Overnight olfactory enrichment using an odorant diffuser improves memory and modifies the uncinate fasciculus in older adults, Frontiers in Neuroscience, vol. 17, 2023. DOI: 10.3389/fnins.2023.1200448