Remembering Smell by Bonnie Blodgett

Author:Bonnie Blodgett [Blodgett, Bonnie]
Language: eng
Format: epub
Publisher: Houghton Mifflin Harcourt

Next questions: How is the pheromone signal processed? How does it enter the brain and what gene decodes it and where does it go? An organ that Richard Axel calls "the erotic nose"—this is the vomeronasal organ (VNO)—is widely believed to be in charge of processing pheromones in most animals. The VNO is not the same thing as the olfactory organ, though it is located in the nasal cavity and operates, Catherine Dulac suspects, in concert with the smell system. The VNO is a chemosensory organ, meaning that it detects and responds to certain chemical stimuli, such as pheromones. In Dulac's model, the vomeronasal pathway "serves as a switch that represses male behavior while promoting female behavior. While male and female bodies are strikingly different physiologically, it appears the same cannot be said for the brain."

Dulac and her colleagues have shown that the mouse olfactory epithelium and the VNO together play a critical role in signaling for sex. Their job isn't to tell male from female but to trigger sexual behaviors. Dulac's hunch is that humans are no different from rodents in this respect; the only variation is that in humans, the olfactory system alone processes such signals and does so without any connection to consciousness. Others disagree. Some scientists argue that if the VNO is the organ that handles pheromone signals, it's unlikely that humans have pheromones. Why? A human doesn't have much of a VNO. It atrophies before birth. While recent studies indicate the VNO may be operational even in its truncated form, Dulac thinks the whole issue is a red herring. So what if we don't process pheromones the way other animals do? Couldn't they be processed along the same pathway as smell?

This brings us back to Leonora. According to Dulac, a woman doesn't know that a man's scent is attracting her because there is no direct neuronal link between the olfactory cells assigned to the task and the higher brain. As Dulac explains, "Our data contradict the established notion that VNO activity is required for the initiation of male-female mating behavior." This, she says, is the key difference between pheromones and the odors commonly mistaken for them, and it's why she doesn't think pheromone responses are the result of training. She argues that while odor signals are distributed throughout the brain, even up to the cortex, pheromones take the express route to organs in the limbic system that prepare the body for sex through changes in the sweat glands, breathing, heart rate, and so on.

In 2006 Linda Buck wrote that VNO receptors were functionally distinct from odorant receptors and that they appeared "to be associated with the detection of social cues." She reported finding a second class of pheromone-linked receptors in the olfactory epithelium that could be central to the reproductive process in mice. This new class of chemosensory receptors suggests that humans too may respond to certain volatile compounds outside of the standard repertoire.

In a joint study published in Nature in 2007, Rockefeller University and

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