Restoring scents: faulty sniffers may get help

Science News, July 7, 2007 by Janet Raloff

Betty (not her real name) remembers the day 9 years ago when she fully experienced an orange. As she split the fruit's skin, the sections, citrus scents sprayed into the air and the 51-year-old woman experienced a sensory epiphany: "Whoa! This is an orange. My God, this is what an orange smells like."

Even now, she says, recalling that day "makes me tear up because that orange was the very first thing I smelled." Ever.

"There are probably around 25 million people in this country who have some olfactory problem" observes Barry Davis, who directs the taste and smell program at the National Institute on Deafness and Other Communication Disorders in Bethesda, Md.

Few people lack all sense of smell. Among these, Davis notes, only a tiny share were either born that way, as Betty was, or lost olfaction so early that they can't recall being able to smell.

More common is a gradual diminution of olfaction among seniors, notes Beverly J. Cowart, a sensory psychologist at the Monell Chemical Senses Center in Philadelphia. By age 70, she says, "some degree of smell loss will be close to universal."

Smell loss can also follow head trauma, arise as a complication of respiratory or brain disease, or signal pollutant poisoning of nasal cells.

Many research programs are not only probing what underlies loss of the sense of smell, but also investigating ways to restore it. Strategies to achieve that goal include drug therapy, sniff training, and even reseeding the nasal lining with stem cells.

Prodding the research is recognition that good olfaction can be a lifesaver, enabling people to detect gas leaks or pick up putrid warnings from spoiled food.

But for Betty, the main benefit has been an improved quality of life. She's building an inventory of identifiable scents--from the fragrances of new-mown grass and roses, to the odor of a cat box. "I love that I can smell them all," she gushes. "Well, maybe not the cat box."

TASTE VERSUS FLAVOR Jason Feifer, an associate editor at Boston magazine, can't smell a thing. However, he wasn't aware of this sensory deprivation until he was in college and a girlfriend began constantly asking for his opinions on foods. It didn't take long for him to realize that she was responding to cues that he couldn't even vaguely detect.

"My taste buds work fine," Feifer points out. "So I can detect sweet, salty, sour, and bitter." Add in color, texture, and mouth feel--such as the smoothness of high-fat fare--and he could easily explain why he preferred some foods over others.

But blindfolded, he says, "I can't tell the difference between mint and peanut butter--cup ice creams." Fruits are sweet to Feifer, but with eyes closed, he can only guess their identity on the basis of texture and acidity.

He now suspects that when he can see what he's eating, "my mind fills in some level of sensation that helps me differentiate between foods."

"In fact, what most people call taste is really flavor," a combination of the taste buds' input with tactile impressions and scents, explains neurologist Robert I. Henkin, director of the Taste and Smell Clinic in Washington, D.C. Eliminate scents, Henkin says, and cherry, mint, and butterscotch candies all taste the same.

SMELL KILLERS Feifer divulged a scary anecdote about the seriousness of his sensory deficit in the Nov. 1, 2005, Washington Post. While he was in the kitchen, his girlfriend called to him from another room to ask whether something was burning. "I said no," Feifer recalls, and when his girlfriend asked if he was sure, he replied emphatically, "Yes, ma'am."

In fact, a malfunctioning electric grill just inches away from him had begun spewing stinky, black smoke.

The episode prompted Feifer to get a thorough checkup at the taste and smell clinic of the University of Connecticut in Farmington. The good news: He got a clean bill of health--no brain tumor, serious congenital disease, or other detectable source of smell loss. But those negative findings also implied that he could expect no cure.

A host of conditions can trigger smell loss. Indeed, the olfactory system is fairly vulnerable, as it's the only one of the human senses involving nerves from the brain that make contact with the outside world--on the inside the nose.

Those thin, spaghettilike nerves run from the nose through an opening in a skull segment called the cribiform plate. Head trauma can sever the nerves, or if an injury shatters the plate, its aperture may close as the bone mends.

Severed olfactory nerves have the capacity to regenerate. If they reconnect to the brain, smell can return, notes James E. Schwob of the Tufts University School of Medicine in Boston. But if their conduit through the cribiform plate closes, smell loss will be irreversible.

Other major reasons for smell loss are respiratory infections and allergies. In rare cases, Schwob says, germs can move up the nerve and into the olfactory bulb, a relay station through which nerve signals enter the brain. If germs damage that bulb, scent data may not reach the tissues able to interpret them.