The ability to smell provides the brain with key information because it allows us to detect potential dangers, such as smoke from a fire, and also to enjoy pleasant sensations such as the smell of a freshly baked cake or freshly brewed coffee, but the loss of smell of rapid form could indicate the deterioration of cognitive functions and the development of brain changes associated with Alzheimer’s and other dementias.
Alzheimer’s disease affects around 800,000 people in Spain, according to data from the Spanish Society of Neurology (SEN), and it is estimated that its prevalence will continue to increase over the next 20 years, in part due to the aging of the population. The symptoms of Alzheimer’s that usually warn of its presence are memory loss, mood swings and difficulties in carrying out daily activities, but when they begin to manifest, the brain has long been damaged.
Researchers at the University of Chicago Medicine have now discovered a new clue that may predict the development of Alzheimer’s and other types of dementia: a rapidly diminishing sense of smell. The results of their study, published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association, reveal that a reduction in a person’s sense of smell over time can predict loss of cognitive function, but also structural changes in areas of the brain relevant to Alzheimer’s disease and dementia, suggesting that tests to assess smell could be developed to detect cognitive decline early.
“This study provides another clue as to how a rapid decline in the sense of smell is a really good indicator of what will end up happening structurally in specific regions of the brain,” said Dr. Jayant M. Pinto, professor of surgery at the University of Chicago, an otolaryngologist who studies olfactory and sinus disease and lead author.
Memory, sense of smell and dementia
Memory plays a key role in our ability to recognize odors, and a link between the sense of smell and dementia has long been known. The amyloid beta plaques and neurofibrillary tangles characteristic of Alzheimer’s disease often appear in areas of the brain associated with smell and memory before developing in other parts of the brain.
It is not yet known whether this damage actually causes a person’s decreased sense of smell, and the authors of the new study wanted to see if it was possible to identify alterations in the brain that correlate with a person’s loss of smell and cognitive function over time. “Our idea was that people with a rapidly declining sense of smell over time would be in worse shape, and more likely to have brain problems and even Alzheimer’s itself, than people who were slowly losing or maintaining a sense of smell. normal smell,” explained Rachel Pacyna, a fourth-year medical student at the University of Chicago Pritzker School of Medicine and lead author of the study.
A rapid decline in sense of smell predicted many features of Alzheimer’s, including decreased gray matter volume in areas of the brain related to smell and memory
The researchers used anonymous data from 515 older adults enrolled in Rush University’s Memory and Aging Project (MAP), which in 1997 began investigating chronic conditions of aging and neurodegenerative diseases. MAP participants are older adults living in retirement communities or nursing homes in northern Illinois who are evaluated each year for their ability to identify certain odors, their cognitive functions, and possible signs of dementia, among other health parameters. . Some participants also underwent an MRI.
These scientists found that a rapid decline in a person’s sense of smell during a period of normal cognition predicted numerous features of Alzheimer’s disease, including decreased gray matter volume in areas of the brain involved with smell and memory, worse cognition and increased risk of dementia in these older adults. Specifically, the risk of losing the sense of smell was similar to that of being a carrier of the APOE-e4 gene, a genetic risk factor that increases the chances of suffering from Alzheimer’s.
The changes were most notable in primary olfactory regions, including the amygdala and the entorhinal cortex, which is an important input for the hippocampus, a critical site in Alzheimer’s disease. “We were able to show that the volume and shape of gray matter in the olfactory and memory-associated areas of the brain of people with rapid decline in sense of smell were smaller compared to people who had less olfactory decline. severe”, declared Pinto.
Smell tests to detect signs of dementia
Pinto and his team intend to perform autopsies to examine brain tissue and look for markers of Alzheimer’s disease. And they also want to see if using smell tests in clinics, just as vision and hearing tests are used, would make it possible to detect and track older adults for signs of early dementia that would help develop new treatments.
The smell tests consist of a series of marker-like sticks, each of which is infused with a distinctive scent that people must identify from a set of four options. It is a cheap and easy-to-use tool in clinical practice. “If we could identify people in their 40s, 50s and 60s who are most at risk early on, we might have enough information to enroll them in clinical trials and develop better drugs,” Pacyna said.
Because the participants only had an MRI during the study, the researchers had no data to determine when the structural changes in the brain began or how quickly brain regions shrank. “We have to take our study in the context of all the risk factors we know about Alzheimer’s disease, including the effects of diet and exercise,” Pinto explained. “The sense of smell and the change in the sense of smell should be an important component in the context of a number of factors that we believe affect the brain in health and aging.”
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