Brett Smith for redOrbit.com — Your Universe Online
The majority of the scientific community has embraced the idea of different smells being based on the olfactory receptors´ ability to detect various shapes of odor molecules.
However, a new study in the open access journal PLOS ONE has given credence to a less popular theory; that the sense of smell is based on the molecules´ different vibrations, not their shapes.
The idea of a quantum, or vibration, basis for olfactory was first put forward by Luca Turin, currently of the Fleming Biomedical Research Sciences Center in Greece, in a 1996 study. Turin posited that molecules are made of a collection of atoms that interact like a set of springs. In the presence of a certain odiferous molecule, an electron within a smell receptor transfers a quantum of energy into one of the molecule’s bonds — setting off the “springs.”
The majority of olfaction scientists dismiss this theory for lack of evidence.
The new study, which credits Turin as one of its co-authors, tested to see if humans could detect the difference between two identically-shaped molecules that were vibrating differently. This was accomplished by replacing hydrogen atoms in a smell molecule with deuterium, a heavier isotope of hydrogen.
Previous research in Nature Neuroscience said human test subjects couldn´t detect a difference. Yet in 2011, Turin and some colleagues found fruit flies were able to tell the difference.
The latest study differs from the Nature study by using a larger pair of molecules — cyclopentadecanone — with more hydrogen or deuterium bonds to amplify the desired effect. The team also used double-blind tests, meaning neither the proctors nor the participants knew which sample was being administered. In this scenario, the subjects were able to distinguish between the two differently vibrating molecules.
While these findings don´t completely vindicate Turin, they do support his initial theory, yet some scientists have already come out to denounce the new study.
“I like to think of the vibration theory of olfaction and its proponents as unicorns. The rest of us studying olfaction are horses,” Leslie Vosshall of The Rockefeller University in New York and co-author of the Nature Neuroscience study told the BBC.
“The problem is that proving that a unicorn exists or does not exist is impossible. This debate on the vibration theory or the existence of unicorns will never end, but the very important underlying question of why things smell the way they do will continue to be answered by the horses among us,” she added.
However, some scientists weren´t so quick to dismiss Turin´s findings, adding no one has been able to positively identify the olfaction mechanism.
“(T)he fact is that nobody has been able to unequivocally contradict (Turin),” Jacob said. “There are many, many problems with the shape theory of smell – many things it doesn’t explain that the vibrational theory does.”