17 Nov , 17:35
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The secret connection between smells and neurodegeneration: why loss of smell may herald serious brain diseases
Smell is one of the least studied and underestimated senses. It is directly connected to brain regions responsible for emotions and memory: signals from olfactory receptors immediately travel to the olfactory bulb located in the forebrain. This is why smells can trigger strong emotional responses - and also easily disappear during a cold or age-related changes. However, the loss of ability to sense smells may not just be a temporary inconvenience. Increasingly, scientists view it as one of the earliest signs of neurodegenerative diseases, including Parkinson's and Alzheimer's.
As reported by TUT.AZ, this is according to The Conversation.
Shocking statistics show that up to 90% of people with Parkinson's disease note a decline in smell many years before motor disturbances appear. By the time classic symptoms emerge - tremor or rigidity - half of the dopamine neurons have already irreversibly died, and the disease has progressed to an advanced stage.
Loss of smell could be a valuable biomarker that would allow detection of the disease at the earliest stage. But this symptom is too nonspecific - it can be caused by age-related changes, viral infections, stress, or damage to the mucous membrane.
Nevertheless, new research reveals a striking pattern: in some patients, the disease may actually begin in the olfactory bulb. Brain areas vulnerable to viruses, toxins, or pesticides may be the first to malfunction - and then pathological changes spread to zones responsible for movement.
In Alzheimer's disease, early disturbances are often associated with damage to the locus coeruleus in the brainstem. This structure is responsible for wakefulness and emotional reactions and is closely connected to the olfactory system. When this interaction weakens, the ability to perceive smells deteriorates - long before memory lapses appear.
Some Parkinson's patients also experience olfactory hallucinations - phantom smells of smoke, tobacco, wood. Meanwhile, real strong smells, such as rubber, smoke, or soap, become barely noticeable. Interestingly, they can still normally sense aromas of chocolate or coffee.
A few years ago, a phenomenon that initially seemed incredible became known: a specific "smell of Parkinson's," described as woody-musky. It was first detected by Joy Milne from Scotland - twelve years before her husband's diagnosis. Later, scientists confirmed: the chemical composition of sebum in patients does indeed change.
For doctors, olfactory disturbances are an important reference point in complex differential diagnosis between Parkinson's disease and other movement disorders. And for researchers - a chance to study one of the most vulnerable zones of the brain.
