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Scientists on the trail of sense of smell

"A rose by any other name would smell

"A rose by any other name would smell as sweet," quoth Shakespeare's Juliet. But ah, the science behind how humans perceive and identify such sweetness is a very complex matter, say Cold Spring Harbor Laboratory researchers studying the sense of smell. Credit: Alamy

Researchers at Cold Spring Harbor Laboratory, in a groundbreaking hunt to map the origins of humans' sense of smell, have found that olfaction relies on multiple regions of the brain — many undiscovered — and is far more complex than previously thought.

“We are in the 21st century and we still don’t really understand the sense of smell,” said Dr. Florin Albeanu, whose research paper, published this week in the journal Nature Neuroscience, challenges prevailing wisdom and poses new questions.

The neuroscientist and his team have found that olfaction occurs throughout the brain, well beyond the olfactory bulb — the structure that receives information about an odor as scented molecules travel from the nose and nasal cavity along highly specialized receptors.

Their efforts come as medical scientists worldwide seek to unravel links between a declining sense of smell and memory loss in people with Alzheimer’s disease. The ability to smell decreases early, and significantly, in Alzheimer’s and other forms of dementia, numerous studies have found.

Doctors long have described the olfactory sense as the portal to human memory. Historically, however, much more data have been gathered about how vision functions than how odors are perceived. For example, medical science has a deeper understanding of the mechanisms involved in the perception of light and precisely how the primary colors red, green and blue are discerned by the brain.

“We want to find the red, green and blue of olfaction,” Albeanu said.

He and the team are mapping sites in the brain as they learn which regions hold the keys to the sense of smell and seeking to determine the step-by-step process by which odors are perceived and identified.

Anyone with an intact sense of smell can recognize the difference between the scent of a rose and that of rotting garbage. But what are the chemical cues that instantly allow the brain to distinguish between the two? The answer to the mystery of explaining how the olfactory sense extracts chemical information is long overdue and is central to the team's work.

“Olfactory experience is very subjective,” said Alexei Koulakov, also a neuroscientist at Cold Spring Harbor Lab. He is collaborating with Albeanu in a series of experiments to unlock the secrets of how a smell is perceived and interpreted.

“The perception of smells actually depends on the context and on an individual’s prior experience," Koulakov said.

Scientists long have known the basic mechanisms involved in how olfaction works: Odor particles enter the nasal cavity, where they bind to receptor cells in a rapid series of molecular events, leading to the interpretation of an odor.

Albeanu and Koulakov said they only now have begun to unravel the mystery of this complex activity. An investigation into how the olfactory sense parses compounds is being studied.

The two scientists last year won a National Institutes of Health Director’s Transformative Research Award for innovative investigations into how the sense of smell works.

Research funded by the National Institutes of Health at other institutions is looking into how the sense of smell is the gateway to memory and how certain smells can evoke memories from decades earlier in life.