I Hit My Head and I Can't Smell a Thing
While researching Brain Sense, I corresponded with a woman--we'll call her Melissa--who lost her sense of smell in childhood. She related to me some of the challenges she faces in a life without smell. (The technical term for her condition is anosmia.) For a long time, Melissa worked as a hairdresser, but she couldn't smell the fumes of the dyes and perms. The chemicals gave her headaches, although she was unaware of the cause. Once, she accidentally mixed noxious bathroom cleaners, growing faint and dizzy as a result.
Without smell, her sense of taste vanished too. Melissa consumed several bottles of ketchup and vinegar weekly, just to feel as if she might be tasting something. To prevent burned dinners, she relies on family members and smoke detectors in every room. She can't have a gas stove; how could she tell if the pilot light went out?
Melissa isn't alone in her anosmia. It's more common than you might think-and you might have it without knowing it. A five-year study of nearly 2,500 residents of Beaver Dam, Wisconsin, ages 53 to 97, revealed some loss of the smell sense in one quarter of them. The prevalence increased with age, to the point where more than 60 percent of those ages eighty and older were impaired. Fewer than 10 percent of those affected were aware of their sensory loss.
Melissa lost her smell sense after a head injury. Anosmia in such cases doesn't usually get much attention, but now a new study from the Université de Montréal, the Lucie Bruneau Rehabilitation Centre, and the Center for Interdisciplinary Research in Rehabilitation of Greater Montreal has been published in the journal Brain Injury. The study reports the results of tests on 49 people with traumatic brain injury (median age of 43). The researchers found that 55 percent of their subjects had an impaired sense of smell, but only 41 percent of them were unaware of their smell-sense deficit.
Where and how is the brain damaged when the sense of smell is lost? Some researchers have used magnetic resonance imaging (MRI) to examine the brains of head trauma anosmics. In one study, scans showed injuries to the brain's olfactory (smell) bulb and tract in 88 percent of cases, to the subfrontal region of the brain in 60 percent, and to the temporal lobe in 32 percent (see diagram).
Generally, the volume of the brain's olfactory bulb is smaller in anosmic patients who have experienced head injuries. Some doctors think the reason may be damage to the axons of the nerve cells that run from the sensory neurons of the nose into the brain's olfactory processing centers. Scent-detection abilities appear to relate directly to the size of the olfactory bulb. German researchers captured MRIs of the brains of 13 patients who experienced partial loss of the smell sense. In the patients who improved over a period of 19 months, the olfactory bulb of the brain increased in volume.
Melissa has been living with anosmia since she was hit by a car at age 12. Soon after the accident, she realized she couldn't smell grandma's cookies, dirty laundry, or burning leaves. Today, in her adult life, her brain lets her forget about her anosmia most of the time, but sometimes her body reminds her of what she's lost. Occasionally, she experiences a tantalizing whiff of a flower or a food. "When I can smell, [the sense] passes in a micromoment, and it is only once in a blue moon," she says, Melissa is one of the fortunate ones; she has learned to cope with her anosmia. Some people aren't so lucky. Anosmia can have serious psychological effects, including feelings of physical and social vulnerability and victimization. People with anosmia can develop eating disorders because their food loses its flavor. Anosmics can feel alone and misunderstood, with all the zest gone from their lives-both literally and figuratively.
Here's hoping that the new study out of Montreal will encourage more researchers to investigate sensory loss after head injury and to look for ways to ameliorate anosmia.
For more information:
Faith Brynie. Brain Sense (Amacom, 2009).
Audrey Fortin, Mathilde Beaulieu Lefebvre, and Maurice Ptito. "Traumatic Brain Injury and Olfactory Deficits: The Tale of Two Smell Tests!" Brain Injury (2010) 24 (1): 27-33.
Eric H. Holbrook and Donald A. Leopold, "Anosmia: Diagnosis and Management," Current Opinion in Otolaryngology & Head and Neck Surgery (2003)11:54-60.
C. Murphy, C. R. Schubert, K. J. Cruickshanks, B. E. Klein, R. Klein, and D. M. Nondahl, "Prevalence of Olfactory Impairment in Older Adults," Journal of the American Medical Association (November 13, 2002) 288 (18):2307-12.
Antje Haehner, Antje Rodewald, Johannes C. Gerber, and Thomas Hummel, "Correlation of Olfactory Function with Changes in the Volume of the Human Olfactory Bulb," Archives of Otolaryngology Head and Neck Surgery (2008) 134(6):621-4.