07.06.07
Restoring the sense of smell
The idea of someone blind being able to see again is something most of us have considered—or the deaf person able to once again hear. But the sense of smell is so basic and fundamental that to lose it is awful, and to regain it… Science News:
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.
But the most common causes of smell loss in middle age, says Davis, are chronic inflammation of the nose due to infections and obstructions by growths called polyps. The latter can be surgically removed to restore smell. Steroids, which turn off inflammation, may also bring a rapid return of smell.
However, Davis notes, “sometimes chronic nose infections lead to permanent damage.” In those cases, scent receptors in the nasal lining may disappear. Local stem cells should replenish those receptor nerves—except that the stem cells may also disappear. When this happens, he says, “there’s no hope” of smell restoration—at least not yet.
Smell factors
Despite the generally grim prognosis for many smell-deprived individuals, there are emerging glimmers that some long-time sufferers will, like Betty, be cured.
Marcia Naomi Berger said,
24 July 2007 at 3:40 pm
I havea friend who lost his sense of smell after his mother died. Has research or anecdotal study found a connection between loss of sense of smell and the suppression of emotion around painful events. I have a feelng that he has not done much grief work around his loss and wonder whether to refer him for psychotherapy, and if yes, what sort would be indicated (hypnotherapy, EMDR, Cognitive Behavior Therapy, or ?? ) Thank you.
Marcia Naomi Berger, LCSW
LeisureGuy said,
24 July 2007 at 3:50 pm
Interesting thought. It’s certainly clear that the brain can shut down senses (wholly or partially) to avoid various kinds of pain—for example, the studies showing how people averse to seeing nakedness can somehow ignore parts of a photo or painting that depict it. And I believe I recall reading about hysterical blindness:
So it was seem possible on the surface that the sense of smell could similarly be turned off. I think a call to a good university medical school teaching psychiatrist might give you some good information.
And I also think the book by Daniel Goleman, Vital Lies, Simple Truths might be useful in this connection. It’s a quick read.
LeisureGuy said,
24 July 2007 at 3:58 pm
You also might want to contact some of these people, mentioned in the references attached to the article quoted in the post:
References:
Chen, X., H. Fang, and J.E. Schwob. 2004. Multipotency of purified, transplanted globose basal cells in olfactory epithelium. Journal of Comparative Neurology 469(Feb. 16):457-474. Abstract available at http://dx.doi.org/10.1002/cne.11031.
Frank, R.A., et al. 2006. Characterization of the sniff magnitude test. Archives of Otolaryngology–Head & Neck Surgery 132(May):532-536. Available at http://archotol.ama-assn.org/cgi/content/full/132/5/532.
Hahn, C.-G. . . . N.E. Rawson. 2005. In vivo and in vitro neurogenesis in human olfactory epithelium. Journal of Comparative Neurology 483(March 7):154-163. Abstract available at http://dx.doi.org/10.1002/cne.20424.
Henkin, R.I., and L.M. Levy. 2002. Functional MRI of congenital hyposmia: Brain activation to odors and imagination of odors and tastes. Journal of Computer Assisted Tomography 26(January-February):39-61. Abstract available at http://www.jcat.org/pt/re/jcat/
abstract.00004728-200201000-00008.htm.
Hummel, T., et al. 2005. “Olfactory training” in patients with olfactory loss. Association for Chemoreception Sciences meeting. April. Sarasota, Fla.
Wilson, R.S., et al. 2007. The relationship between cerebral Alzheimer’s disease pathology and odour identification in old age. Journal of Neurology, Neurosurgery, and Psychiatry 78(January):30-35. Abstract available at http://jnnp.bmj.com/cgi/content/abstract/78/1/30.
Yee, K.K., and N.E. Rawson. 2000. Retinoic acid enhances the rate of olfactory recovery after olfactory nerve transection. Developmental Brain Research 124(Nov. 30):129-132. Abstract available at http://dx.doi.org/10.1016/S0165-3806(00)00108-5 .
Further Readings:
Christensen, D. 2000. Making scents of Alzheimer’s. Science News 158(Oct. 21):269. Available to subscribers at http://www.sciencenews.org/articles/20001021/note14.asp.
Féron, F., et al. 2005. Autologous olfactory ensheathing cell transplantation in human spinal cord injury. Brain 128(December):2951-2960. Abstract available at http://brain.oxfordjournals.org/cgi/content/abstract/128/12/2951.
Murrell, W., et al. 2005. Multipotent stem cells from adult olfactory mucosa. Developmental Dynamics 233(June):496-515.
Smell Disorders
http://www.nidcd.nih.gov/health/smelltaste/smell.asp.
Travis, J. 1999. Making sense of scents. Science News 155(April 10):236. References and sources available at http://www.sciencenews.org/pages/sn_arc99/4_10_99/bob2ref.htm.
Yee, K.K., and N.E. Rawson. 2005. Immunolocalization of retinoic acid receptors in the mammalian olfactory system and the effects of olfactory denervation on receptor distribution. Neuroscience 131(3):733-743. Abstract available at http://dx.doi.org/10.1016/j.neuroscience.2004.11.011 .
Sources:
Beverly J. Cowart
Monell Chemical Senses Center
3500 Market Street
Philadelphia, PA 19104-3308
Barry Davis
National Institute on Deafness and Other Communication Diseases
National Institutes of Health
6120 Executive Boulevard
Bethesda, MD 20892
Robert A. Frank
University of Cincinnati
Graduate School, ML 627
Cincinnati, OH 45221-0627
Thomas Hummel
Smell & Taste Clinic
Department of Otorhinolaryngology
University of Dresden Medical School
Fetscherstrasse 74
01307 Dresden
Germany
Nancy E. Rawson
Monell Chemical Senses Center
3500 Market Street
Philadelphia, PA 19104-3308
James E. Schwob
Anatomy and Cellular Biology
Tufts University School of Medicine
136 Harrison Avenue
Boston, MA 02111
The Taste and Smell Clinic
5125 MacArthur Boulevard, N.W., #20
Washington, DC 20016
Robert S. Wilson
Rush Alzheimer’s Disease Center
Rush University Medical Center
600 S. Paulina, suite 1037
Chicago, IL 60612
Olivier Lichtenberger said,
14 September 2007 at 5:01 pm
Hi LeisureGuy,
You shall find another reference about anosmia on my site. My anosmia is a toxic one. And I fear it concerns almost all anosmic and non anosmic. It concerns this flavor tempered culture of ours. It concerns that food tempered epoch.
An soybean is stinky stuff.
Total anosmia is rather rare but wronged olfaction is the norm in our chemical times.
O. L. Lyon Presqu’Île.