A recent study has found that a loss of the sense of smell may be one of the earliest and most important symptoms of Alzheimer’s disease, and surprisingly, it may appear even before obvious memory problems.

According to this study, the brain’s immune system plays a key role in this process, but the problem is that it sometimes mistakenly attacks the very nerve fibers that are essential for the sense of smell.

The study, published in Nature Communications, includes evidence from both mice and humans, such as brain tissue analysis and PET scanning. The findings could not only improve early diagnosis of the disease but also open new doors for timely treatment.

According to researchers, smell problems arise when immune cells in the brain, called microglia, begin to disrupt communication between two key areas: the olfactory bulb and the locus coeruleus.

The olfactory bulb, located in the forebrain, processes signals from smell receptors in the nose. The locus coeruleus, located in the brainstem, helps control this process through long nerve fibers.