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All senses -

Humans have long known the vital role our sense of smell plays in navigating the world. Like other mammals, we rely on our olfactory system to assess our surroundings. This allows us to determine if food is safe to eat, for example.

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Survival tool -

Crucially, our sense of smell helps us identify potential dangers, such as smoke. When we detect these threats, our limbic system immediately alerts us to the danger.

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Brain message -

Dr. Brett Osborn, a neurosurgeon at St. Mary's Medical Center in West Palm Beach, Florida, explains that our sense of smell directly connects to the limbic system, the part of our brain that controls our emotions and instincts. This explains why we're often driven to flee from perceived threats like chemical exposure.

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Memory lane -

Dr. Osborn emphasizes that the strong link between the limbic system and our sense of smell explains why smells are so powerfully linked to memory. "Odors often stimulate memories," Dr. Osborn explains.

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Smells like Christmas - They can also evoke strong emotions, both positive and negative. This explains why the holidays often evoke a sense of nostalgia, triggered by the familiar scents of the season, like pine needles and baking spices.

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Emotional scents -

Or how vivid memories can be triggered by the scent of a familiar perfume, instantly transporting you back to a loved one, or the aroma of a dish that instantly conjures up cherished family moments.

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What's the link to our brains? -

Smelling triggers the brain's complex olfactory network. When we inhale the scent of a rose, for example, receptors in the nose pick up the various molecules that create its fragrance.

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How does it work? -

This information is sent to several regions of the brain, including the olfactory bulb, olfactory cortex, hippocampus, thalamus, and orbitofrontal cortex, all of which help us process the odor.

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How does it work? -

In the olfactory system, each nasal cavity houses special cells that can detect different odors. When odorous molecules stimulate it, nerve signals are sent to the brain, where the odors are analyzed and connected to emotions and memories.

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Memory connection -

To identify the rose's scent, for example, we rely on our memory of its unique pattern of odor molecules from past encounters.

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Declining function -

Because it is closely linked to brain function, the sense of smell has been studied for years. Researchers have found that, much like hearing and sight, our sense of smell tends to decline as we age, often correlating with a decrease in cognitive abilities.

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Declining function -

As we age, many people experience a decline in their sense of smell, known as olfactory dysfunction. Older adults may struggle to identify or distinguish between different odors, and in some cases they might lose the ability to detect odors altogether.

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Cognitive decline -

When no clear medical cause is found, a weakened sense of smell can serve as an early warning sign of cognitive decline. Studies show that older adults who struggle to identify familiar odors are twice as likely to develop dementia within five years compared to those with a healthy sense of smell.

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Cognitive decline -

Difficulty identifying odors is also common in individuals with neurodegenerative conditions, such as Alzheimer’s disease.

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Recent findings -

Building on the link between smell and brain function, a recent study by researchers at the University of Navarra in Spain revealed that a specific scent might help slow the cognitive decline associated with Alzheimer's disease.

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Menthol's potential -

Researchers discovered that when mice with Alzheimer's disease inhale menthol, their cognitive abilities improve. The study’s team believes this finding highlights the potential for using specific scents as a therapeutic approach for Alzheimer's.

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Getting sharper -

Previous research demonstrated that inhaling menthol boosted the immune response in mice. Now, scientists have shown that menthol can also enhance cognitive function in these animals, as confirmed through a series of laboratory tests.

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Promising results -

In mice with Alzheimer's disease, a six-month menthol treatment effectively halted the decline in cognitive abilities and memory. Furthermore, the study suggests that menthol normalized the levels of the inflammatory interleukin-1-beta (IL-1β) protein in the brain.

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Curbing inflammation -

IL-1β is a protein that plays a crucial role in the body's inflammatory response. While inflammation is a natural defense mechanism, excessive inflammation can be harmful.

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Inflammation and aging -

As we age, an imbalance arises, with an overproduction of pro-inflammatory molecules and a decline in anti-inflammatory ones. This chronic inflammation can damage multiple systems, including the cardiovascular, nervous, and metabolic systems, accelerating the aging process.

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Right chemistry -

This explains why researchers are hopeful about menthol's potential. The chemical compound has proven effective in reducing inflammation, supporting the immune system, and stimulating brain pathways, offering a promising approach to treating cognitive decline.

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More tests -

In addition to the menthol approach, researchers observed similar effects by artificially reducing the number of T regulatory cells (Treg), which normally suppress immune activity.

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Effective methods -

Both the menthol approach and reducing Treg cells lowered IL-1β levels, a protein associated with cognitive decline, explained neuroscientist Ana García-Osta from the Center for Applied Medical Research (CIMA) in Spain.

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Positive for all -

Researchers found that the cognitive improvements weren’t limited to mice with Alzheimer’s. Blocking this protein with a drug used for some autoimmune diseases also enhanced cognitive function in healthy mice.

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Connected systems -

As diseases like Alzheimer's, Parkinson's, and schizophrenia have been linked to olfactory dysfunction, this study is a "crucial step towards understanding how the immune system, the central nervous system, and our sense of smell are interconnected," said immunologist Noelia Casares from CIMA.

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Alzheimer's and beyond -

"The results suggest that odors and immune modulators may play an important role in the prevention and treatment of Alzheimer's and other diseases related to the central nervous system," highlighted Casares.

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Further research -

While this new research shows promising results, the authors stress that more studies are needed in both mice and humans.

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In the meantime -

Existing evidence suggests that olfactory training can already yield positive results. This involves regularly smelling a variety of strong odors from different categories, such as flowers (rose), fruits (lemon), herbs (eucalyptus), and spices (cloves).

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Smell training -

Participants may be asked to identify, detect, or simply focus on these odors. Training sessions should be conducted daily for several months, with at least three months recommended for older adults.

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Brain health -

A recent study on olfactory training in older adults found it not only boosted their ability to identify smells, but also improved other cognitive skills. For example, those who underwent smell training showed better verbal fluency, such as naming words linked to a category, compared to control participants who did Sudoku exercises.

Sources: (ScienceAlert) (The Conversation) (Medical News Today) (Incite Health)

See also: Habits you didn't know could damage your brain

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