Tracking THE Scent : A sniff can turn you hungry or warn you to run. Dr. James Evans is studying why some people’s sense of smell stinks.

It only happens now and then, and only for a few precious seconds: the quickest whiff of blooming flowers, of coffee brewing, of bacon grilling, of freshly cut grass. Then, nothing. No smells at all. Not noxious odors, not glorious, evocative scents.

That’s what it’s like for Toni La Motta of San Diego. One tantalizing perception, then her olfactory mechanism, for some reason, shuts down. It’s been like that, she says, since high school, more than 30 years ago.

And, until recently, she never found a doctor who seemed to care.

“It’s very annoying to me that the medical profession has ignored it,” La Motta said. “It’s like it’s really not an issue. Most doctors, when you tell them you have no sense of smell, say, ‘So what? Live with it.’ ”

But not Dr. James Evans of UC Irvine. Instead, Evans will seal you inside a dark, soundproof cubicle, stick electrodes all over your head, wire you up to a lab full of computers and diagnostic gizmos, stick a plastic tube into one of your nostrils and blow various scents into your nose.

Evans, an assistant professor of neurology and the director of the Chemical Senses Clinic at UCI, is out to help people such as La Motta smell the roses.

Since 1987, Evans has been researching the brain triggers (he calls them “olfactory-evoked potentials”) that allow us to distinguish smells; about a year ago he developed an intricate and highly sensitive system to measure olfactory perception. In recent months, he has used the high-tech system to measure olfactory and neurological responses in some 70 test patients, from head injury victims to allergy sufferers to victims of neurological disease to even more mysterious cases such as La Motta’s.

Through his research, Evans hopes to identify more accurately the causes for loss of smell (and, by extension in most cases, loss of the sense of taste) and develop methods to treat them. It can, he said, be a mysterious process, but he has at least one biological advantage. “One of the interesting things about olfactory nerves,” Evans said, “is that they die and regenerate regularly.” This means that in some cases of loss of the sense of smell, it may be possible to stimulate the growth of olfactory nerves and thereby resurrect that sense.

I n Evans’ lab, he and a group of assistants are refining techniques to differentiate between loss of sense of smell because of trauma to the olfactory nerves (such as a head injury) and loss because of inhalation of toxic substances, or because of allergies or possibly because of neurological disorders such as Alzheimer’s disease. These diagnostic techniques range from measurement of brain activity to the Jelly Belly test.

The Jelly Belly test is actually an informal demonstration of how the olfactory receptors, which are in the upper part of the nose, work.

Evans offers a visitor two or three Jelly Bellies (a popular, small and highly flavorful variety of jelly beans) and asks the visitor to pinch his nose before popping the candy in his mouth. The result: a vague sense that something sweet is in the mouth but there is no discernible taste. However, once the nostrils are released, there is a sudden burst of taste: strawberry, coconut or grape.

This is, Evans said, one way to gauge what is known as “conductive loss” (odors can’t reach the olfactory receptors) and “general loss” (in which the olfactory nerves have been sheared in an accident).

Dorothy Cotton, an 83-year-old test subject from Newport Beach, said she suspects that her inability to smell may be tied to conductive loss.

“It came on slowly,” she said, “and I think it may be tied with my sinuses. It’s been at least 15 years that I haven’t been able to smell.”

In the lab tests, she said, she still could smell nothing. However, she said, Evans recommended she take zinc supplements for two months, discontinue the nose drops she was using and substitute antihistamines to clear her sinuses. Zinc, explained Evans, can be depleted by certain types of viruses that can also affect smell.

“I can taste sweet and sour and salty on my tongue, no problem,” Cotton said after starting the zinc treatments. “But if you blindfolded me I wouldn’t know what I was eating. You learn to appreciate some foods by the sight of them, but eating is a pleasure. I would give a lot to have my taste working again.”

Another rather low-tech test in the lab is called “forced choice,” in which patients are given two small squeeze bottles, one imbued with an odor and the other odorless, and asked to identify the one with the odor. The odors are not all the same strength, however, because researchers have found that “the smelling scale (is) analogous to the decibel scale,” Evans said.

That is, just as there are degrees of deafness, Evans said, one person may be able to smell an odor only in a strong concentration, while another may be aware of it in its weakest strength. For instance, a low concentration of amyl acetate smells like bananas to a subject with healthy olfactory apparatus, while a very strong concentration can smell like airplane glue.

“At different concentrations they have different qualities,” said Evans, “from quite noxious and foul to quite pleasant.”

It has been found, Evans said, that some people suffer from a condition called “specific anosmia,” a kind of olfactory color blindness in which the person cannot smell certain smells but can perceive most others. To test for this, the lab stocks a catalogue of more than 50 aromas.

“There may be no genetic receptor in a person for a certain class of odors,” Evans said. “And it appears to run in families. There are about 150 types of odor receptors, which means that we can identify that many classes of smells.”

Unless something goes wrong. Then patients may find themselves attached to the most advanced of Evans’ testing apparatus.

The entire system measures olfactory evoked potentials (OEP)--brain activity in response to stimulus of olfactory receptors in the nose. Evans said he developed the technique of measuring OEP in rats at UCI in 1987 but has been using the present system, which he also developed for about a year on various human test subjects. At its most basic, the system involves nothing more than air and smell. It’s the measuring that elevates the process.

It works like this: The patient is fitted with several scalp electrodes to measure brain activity and is plugged into a console inside a dark, soundproof booth (the only stimulus Evans wants is through the nose). A small plastic nozzle is fitted into one nostril, and a gentle stream of air is directed through it into the patient’s nose.

For the most part, the airstream is clean. But at intervals, a machine outside the booth emits a click. This means that for 4/100 of a second, what Evans calls “a pulse of odor” is introduced into the stream. Computers measure any brain wave activity that occurs at that instant.

This entire process allows Evans and his researchers to locate, among other things, the possible source of loss of brain response.

Treatment, Evans said, depends on the cause. In the case of a head injury, the nerves may regenerate on their own, or there may be no hope for treatment. Sometimes, he said, traditional respiratory therapy can bring back some function. Polyps, benign growths, allergies, swelling, infections, sinusitis--all can be treated to different degrees.

However, he said, matters become more murky when patients are affected by neural degenerative diseases such as Alzheimer’s disease, Parkinson’s disease and Korsakoff’s psychosis (seen in alcoholics).

“Smells will bring back strong memories to you,” Evans said, “and all of these diseases are associated in some way with memory loss.” Partly because of this, he said, “olfactory loss may be one of the first things to go” in a patient suffering from such diseases. Research is continuing into drug therapy for neural disorders, and Evans called the work “promising.” However, the tie-in remains a mystery.

Depression is common among people with loss of smell, said Evans, although he added that “after years, many resign themselves to it and find ways of stimulating what receptors they have with salt and spices.” Still, there is yet another factor to consider: safety. Without a sense of smell, fires and natural-gas leaks can go unnoticed.

La Motta knows this.

“I remember an incident in high school,” said La Motta, a 48-year-old writer and teacher who participated in Evans’ research, “when we were doing a hydrogen sulfide experiment, and I couldn’t smell anything in the lab.” Later in life, she said, “I’d be in the living room and there would be smoke all over from the kitchen. I’d be reading and absorbed and not even notice. One of my major problems today is that I burn things frequently in the kitchen.

“There are some times when it’s scary, especially if I leave the house and don’t know something’s burning. And the (cat box) is worrisome. My friends have to tell me to change the (cat-box filler).”

During her testing at UCI, La Motta said she “felt” the smell in her nose during her time in the booth but didn’t actually smell it.

“It was fascinating to me, though, because he was actually measuring it. I’ve been through acupuncture, to several doctors. They all said they can cure it, and nobody has. I hope this time it’s different.

“People joke with me all the time and say I’m lucky, but I don’t see it. I can’t smell roses or the spring or the ocean.”

How Sense of Smell Works

Most people can distinguish thousands of different odors, whether foul or fragrant, with a simple sniff of the nose. For people without a sense of smell, food doesn’t taste as good, flowers and perfume evoke no special memories, and potential hazards signaled by noxious odors go unnoticed.

1. Airborne molecules of a rose travel through nasal passages.

2. Molecules dissolve in mucous membrane.

3. Receptor cells are stimulated, then generate nerve impulses.

4. Nerve impulses travel through olfactory nerve to the olfactory bulb.

5. Olfactory bulb analyzes impulses and sends them to brain, which identifies the smell.

A Perfect Match:

Scientists believe the smell process occurs when there is a physical connection between odor molecules and receptor sites. Bleach molecules, for example, would only fit with receptors on some cells, while the odor molecules of a rose would only fit on receptors on the other cells.

Fast Facts:

Women, on average, have a better sense of smell than men.

Older people typically lose their sense of smell.

Changes in ability to smell may be an early sign of Alzheimer’s and Parkinson’s diseases.

Cigarette smoke and other airborne toxins can lessen or distort sense of smell.

People with depression, schizophrenia or other psychological disorders can develop dysosmia, a condition that makes them believe that something pleasant-smelling has a bad odor.

Source: Academic American Encyclopedia, World Book Encyclopedia, American Medical Assn. Encyclopedia of Medicine Researched by CAROLINE LEMKE / Los Angeles Times