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Little-known nerve may be secret to lust

Ted James and Lysa Grant hit it off immediately when they met at a study group for a psychology class. The two students at New York University knew something was special, and four years later they are now engaged.

James, 24, vividly remembers the first thing he noticed about Grant. “I just loved her smile,” he said.

For Grant, the connection was more cerebral. “I could see he was really smart,” she said. “That was a turn-on.”

But according to R. Douglas Fields, neither intelligence nor charm had much to do with their mutual attraction. Rather, a little-known cranial nerve brought them together, he believes. Few neuroscientists are even aware that this so-called nerve zero exists, but Fields, an adjunct professor of neuroscience at the University of Maryland believes it may be the key to lust.

His theory is that nerve zero transmits sex pheromones to the brain. The pheromones are chemicals that one member of a species emits that trigger an innate behavioral response in another member of the same species. They are generally detected by the sense of smell. The notion that smell is important to the sexual drive of animals has long been established, but nerve zero may be the “missing link” that confirms that human beings rely on pheromones, Fields says.

“Human behaviors are much more complex than other animals, but there are several studies showing that the sense of smell does affect sexual behavior in people,” Fields said. “And here is a nerve that connects the nose to the part of the brain involved in sexual reproduction, which helps prove it.”

Pheromones were first discovered in insects in 1959, and later studies suggested that they also induced sexual reactions in people. In 1995, for example, Claus Wedekind, a researcher at the University of Bern in Switzerland, asked a group of women to smell T-shirts worn by men they did not know. They discovered that women preferred the smell of men who had different immune systems from their own, which would enhance the likelihood that they would have healthy children.

Such theories are controversial, if for no other reason than they lack hard scientific evidence. Fields faces a number of obstacles in convincing others of his theory.

Besides the debate over whether sex pheromones even exist, few people in the field know about nerve zero. The nerve was discovered in the human brain in 1913, well after the other 12 cranial nerves. With its dominant position at the top of the brain, researchers called it nerve zero rather than rename all the others.

Being so thin, this obscure nerve is usually overlooked in medical research as it is often stripped away when the brain is exposed for dissection. For this reason, nerve zero doesn’t appear in most neuroscience textbooks or medical brain maps.

"What is that?” said Dr. Carol L. Colby, an associate professor of neuroscience at the University of Pittsburgh, when asked about nerve zero. “I’ve never heard of it.”

For those who know about nerve zero, its function has long been debated. Some scientists believe that it is a branch of the olfactory nerves or that it has lost its purpose over time and now has no use, much like the appendix.

For that reason, the jury is still out in Fields' theory, said Michael Meredith, co-director of the neuroscience program at Florida State University.

“I don’t know that there is good evidence of that,” he said. “There are a lot of ifs, ands and buts. It’s prevalent in all vertebrates, which suggests that it does have a function, but we don’t know that it has an adult function.”

But Fields insists evidence is stacking up that the sense of smell affects one’s choice of sexual partner and that nerve zero is the conduit. He points to a 1987 study on hamsters by Celeste Wirsig, then a postdoctoral fellow at Baylor University. The rodents failed to mate after their nerve zeros were severed. Since the nerve systems of hamsters and humans are similar, it stands to reason, Fields says, that nerve zero has the same purpose.

“You take those facts and form a hypothesis, and that’s exactly where we are,” he said.

Fields has supporters, among them James Kohl, co-author of “The Scent of Eros,” a book on pheromones.

“He’s right on,” Kohl said. "We have known there is some physical link, but [nerve zero] really helps to define it. Maybe a lot of neuroscientists don’t know about it, but people who study the olfactory system and pheromones see that and say that’s really important.”

The thought that they might be together because they “smell right” makes James and Grant a little uncomfortable, although they accept that it’s possible. Even if scent is what got them started, James believes love is much more complicated than a pleasing aroma.

“She’s my soul mate,” he said about his fiancee. “No whiff of sweat is going to make me feel the way I feel about her.”