Working on a national protocol for a new medication for Alzheimer's disease allowed me an opportunity to understand some of the pathology involved. Many decades ago, researchers tested a specific aspect of cognitive decline: the sense of smell.

Prior research had indicated a direct connection between the loss of a sense of smell and the incipient appearance of symptoms of Alzheimer's disease. Many years later, researchers are beginning to explore that connection more vigorously since it may be more fruitful than we ever anticipated.

Memory, cognitive abilities, and brain function can all decline to different degrees as people age, especially around middle age. Notably, dementia and other age-related cognitive decline disorders have been on the rise for several years. Of course, when seeking causes for something such as a neurodegenerative disorder, we immediately look at the environment, diet, and lifestyle, but how many of us look to a person's sense of smell?

Neurodegenerative illnesses are now commonly linked to a diminished sense of smell. While not all individuals with Alzheimer’s, Parkinson’s, Huntington’s, or schizophrenia may experience olfactory abnormalities, these conditions can manifest in certain patients. It is unclear if these symptoms are a result of the disease itself or if they are caused by a malfunctioning olfactory system that promotes neuronal death in many brain locations through circuit changes. Finding olfactory receptors in non-sensory regions of the brain is another component of the olfactory pathway to neurodegenerative disorders.

The number of people diagnosed with dementia is projected to rise from 55 million in 2019 to approximately 139 million by 2050, according to estimates. Therefore, it is critically important to understand what causes cognitive decline and how to identify the early symptoms of dementia so that therapeutic measures can be planned appropriately.

Olfaction, the sense of smell, is related to multiple areas within the central nervous system, many of which are directly related to the development of psychiatric illnesses, neurogenic disorders such as Parkinson's, and even schizophrenia. Studies have indicated that over 139 conditions are in some way related to a sense of smell, including MS, ALS, and other cognitive dysfunction disorders. Other, less understood relationships between smell and a physical disorder include cardiovascular disease, arthritis, and polycystic ovary syndrome. All of these disorders point to the wide range of associations between scent receptors in the body and physical or mental disturbances.

During the pandemic, when COVID-19 was running throughout the United States, people began to understand that a loss of a sense of smell was one of the signs that they may have become infected. In fact, in Alzheimer's research, we have found that smell is one of the first senses affected. In COVID-19, this loss of a sense of smell pointed to the virus having more of an ability to damage our nervous system. We now know that COVID is much more of a serious, probably neurologic infection than previously thought, and that it can linger for a long time. In Alzheimer's, smell pointed to neurologic damage that had already begun, and of which researchers were aware.

In fact, the physical location of our sense of smell and its relationship to other aspects of our lives is paramount. Opposite to sounds, odors travel directly to the olfactory bulb embedded in the forebrain. The bulb is associated with numerous brain regions that play a role in emotional regulation, decision-making, memory, and learning.

While neurological injury certainly accounts for some olfactory impairment, newer studies indicate that a loss of smell may be a contributing component to our reduced total lifespan. This is a scary thought; we would do anything to prolong our lives. We exercise, we watch our diet, and we try to maintain healthy, social relationships, so why not pay some attention to our sense of smell?

Training Our Sense of Smell

Observing the widespread utilization of smell receptors has pointed researchers to a new appreciation of an intriguing and somewhat unusual idea regarding smell and cognition training.

Can we train ourselves in some way to affect the health or preserve the utility of our scent receptors? In other words, is smell a trainable human ability? Undoubtedly, animals have far greater abilities to detect scents outside of human capacity. Still, we are not talking about approaching that level of sensitivity but merely enhancing what we have now.

If we can train our sense of smell, we can protect and preserve our cognition. It sounds rather unusual, or if you prefer, bizarre, but that is what is being considered now. But the current research goes even further, indicating that we may be able to repair or revive smell receptors that may have gone dormant through our aging process. We know that the sense of smell seems to diminish with age, but now there is new hope for our smell receptors.

Research has surged because “smell training” may revive this dormant sense and improve cognitive abilities. Evidence from studies points to the possibility that it can. The more we utilize our sense of smell, the more powerful it becomes, like a muscle.

Could we achieve favorable results in scent training by doing more than just following our noses? Many commercially available smell-training programs seek to achieve that. In most cases, the instructions for using the kits call for the user to spend a few minutes daily sniffing a blend of fragrant compounds, including clove, eucalyptus, rose, and lemon, for a few weeks or months.

Experiments have shown heightened sensitivity to odors with a negligible time commitment. Be patient. For instance, a study indicated that individuals with post-infectious olfactory dysfunction showed substantial recovery in 70% of cases when treated for 56 weeks, compared to 58% when trained for 15 weeks.

While the user sleeps, a partially available device releases 40 distinct aromas. Results showed a 226% improvement in verbal memory following six months of nightly usage in a short experiment that examined an early version on 43 individuals aged 60 to 85. Of course, such a small sample needs to be considered carefully and much larger. We need larger samples to achieve professional acceptance and determine whether this training is practical.