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The Joy of Jacobson’s Organ

September 3, 2008

Ever seen a horse curl its lips back into a big square-toothed grimace (picture Mister Ed pronouncing a multisyllable word)? Or a cat drop its mouth open and appear to zone out into a trance? They’re not doing it just to creep out human beings (although it is pretty creepy). They do these things for the same reason a snake flickers its forked tongue (okay, that’s even creepier). These animals are all demonstrating a behavior known as the flehmen response (from the German flehmen, meaning to curl the upper lip), an action which facilitates the transfer of particularly interesting scents–think pheromones–into the Jacobson’s organ, a chemoreceptor organ found at the base of the nasal cavity. Human beings do not demonstrate the flehmen response–in fact, that sneer made by a flehmening horse on the face of a human would tend to indicate a particularly foul odor rather than an attractive one–but it was in human beings that the Jacobson’s organ was first observed.

Although reports of the organ in the human nose date back to 1703, we learn in Chapter 4 of Whiff! (The Scent of Sex) that confirmation of the Jacobson’s organ’s existence in humans is credited to nineteenth-century Danish physician Ludwig Jacobson, who discovered two tiny pits that lay on either side of the nasal septum, just above each human nostril: “This find was dubbed the Jacobson’s organ and remained an anatomical curiosity for over 100 years. Gradually, as scientists found similar organs in higher animals and related discoveries in reptiles and birds, a hypothesis over the reason for the organ’s existence was formulated. But not much interest was generated by the discovery, and if the organ, later renamed the vomeronasal organ (VNO), was commented upon at all throughout the years, it was described as a leftover evolutionary relic–a non-functioning, unnecessary piece of anatomical equipment.”

And, true, the human VNO, like most olfactory functions, appears to have atrophied somewhat over the years in comparison to that of our fellow living creatures. But “non-functioning”? A little more research might have been in order before tossing out poor ole’ Jacobson’s organ with his tonsils and appendix. And fortunately, much later, there was a little more. Whiff! goes on to tell the story of Dr. David Berliner who, as professor of anatomy at the University of Utah in Salt Lake City in the 1960s, noticed that the researchers in his lab became inexplicably warmer and friendlier when he left Petri dishes of dead skin cells lying about. When the samples were removed, the staff’s normally stiff and less-amiable behavior returned. He was intrigued, but had no idea what to make of this phenomenon until other researchers began investigating the VNO in animals and its importance became evident. “In 1989, Dr. Berliner returned to his study of the VNO and with his associates, he conducted tests wherein he wired the subject’s nasal cavities to an apparatus that read the electrical responses to various substances introduced to the VNO. He tested responses to plain air, an inert pheromone-free solution, a clove mixture, and finally, a synthesized essence of human pheromones. The results? The only reaction noted via the electrical impulses of the VNO came from the synthesized human pheromone substance. The other substances showed a flat line on the machine.” These findings prompted Dr. Berliner to form the Erox Company which, in 1993, launched a set of fragrances which it claims are “the only fragrances that contain human pheromones duplicated in the laboratory and have shown to stimulate the human vomeronasal organ,” thus tapping into the rich market for this relatively unknown “sixth sense.”

Despite the fascinating implications of Dr. Berliner’s study and a handful of others–including one which indicated hyper-stimulation of the VNO in pregnant women, perhaps partially accounting for her improved sense of smell and her morning sickness–conclusions regarding the human VNO remain a matter of controversial debate among researchers, likely because such studies are underfunded and, thus, few-and-far-between. Animal VNO studies are not lacking–a quick google search shows that you can barely swing a dead cat without smacking a study on the VNO of a cat–just human studies. For a species with such a driving curiosity into our own construction, this seems odd.

“As humans, we tend to downplay the importance of our sense of smell,” suggests Dr. Sarah Newman of the University of Michigan, who believes that our reluctance to explore the human VNO stems from a general distaste for the olfactory function as a whole, “even though walking through a drugstore and counting the products that are perfumed or deodorized should be enough to convince anybody that olfaction is important to us.”

The scarcity of concrete research may have another psychological culprit, as well. “People are scared to death of unconscious forces, especially unconscious forces that have anything to do with the opposite sex,” says Biologist David Moran of the University of Pennsylvania Smell and Taste Center. “We like to think we are in control.” This possibility seems also to have occurred to Anne Marie Helmenstine, Ph.D. who concurs with Dr. Berliner in dubbing the workings of the VNO “the sixth sense,” but appears keenly aware of an unfortunate and inaccurate connotation between the terms sixth sense (natural) and ESP (supernatural). “Since extra-sensory perception or ESP is awareness of the world beyond the senses, it would be inappropriate to term this sixth sense ‘extrasensory’. After all, the vomeronasal organ connects to the amygdala of the brain and relays information about the surroundings in essentially the same manner as any other sense. Like ESP, however, the sixth sense remains somewhat elusive and hard to describe.”

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