If you're forgetting something and your sense of smell has changed, take action immediately.

Scientists suggest that Alzheimer's disease may manifest as a diminished sense of smell even before cognitive decline sets in. While previous research has pointed to this connection, the brain mechanisms responsible for this sensory loss have not been fully understood until now.

The brain's immune system cuts off nerve connections

In the new study, researchers analyzed PET scans and tissue samples from both human and mouse brains to understand why Alzheimer's causes smell loss.

The results revealed that the brain's immune system plays a key role in this process. Specifically, immune cells called microglia were observed to sever the neural connections necessary for the sense of smell. These cells sever the connections between the olfactory bulb, which collects olfactory signals from our nose, and the locus coeruleus, a structure in the brainstem.

SMELL SIGNALS CANNOT BE PROCESSED IN THE BRAIN

The olfactory bulb is a forebrain structure that receives signals from olfactory receptors in our nose and transmits them to other parts of the brain. A disruption in this neural communication can lead to premature loss of smell in individuals.

Researchers believe that this Alzheimer's-related smell loss is not just a temporary symptom, but a signal that holds important clues about the disease's progression. In this context, smell tests could become a helpful tool in Alzheimer's screening.