Field of Science


The Sniff Test for Mental Illness

Imagine a patient goes to see his general practitioner, complaining of exhaustion. He can't sleep, and he'd like a referral to a sleep clinic so he can get some answers. First, his doctor wants to administer a quick test. She holds a device like a felt-tipped pen just under her patient's nose and has him sniff. "Sure, I can smell that," he says. She gives him three pens and asks which one smells different from the other two. "They all smell like peppermint to me," the patient says. "Okay," the doctor says, "I'm referring you to a psychiatrist."

This type of test, if it exists someday, would take advantage of the fact that your brain's components aren't just responsible for one job apiece. For example, an area right above your eyeballs called the orbitofrontal cortex is involved in decision making and emotions--and your sense of smell. According to researchers in Belgium, a test of olfactory abilities might be able to alert doctors to an underlying condition such as depression, dementia, or schizophrenia.

Pierre Maurage and his colleagues studied a group of 20 alcoholics who were receiving treatment and hadn't drunk for at least two weeks. Each alcoholic was matched with a control: a person of the same age, sex, and education level who had no history of psychiatric problems or substance abuse.

Subjects took three kinds of tests. The first set of tests measured their olfactory abilities. Subjects were given pens to sniff; researchers assessed their sensitivity to different concentrations of odors, their ability to tell different odors apart, and whether they could correctly identify what they smelled.

Next, subjects took two cognitive tests. In one test, they looked at words on a screen and had to press a button to indicate whether each word was an animal or an object--but if they heard a beep, they had to stop themselves from answering the question. This is a test of general cognitive functioning that doesn't specifically involve the orbitofrontal cortex.

The third test was one that is known to activate the orbitofrontal cortex. Subjects had to view a series of pictures and say whether they'd seen them already or not. Later in the day, they repeated the test, and were asked to forget what they'd seen in the first test. If subjects had trouble remembering whether a picture was familiar because they'd seen it a few moments ago or earlier in the day, they were given a high "confabulation" score. Confabulation is the tendency to fill gaps in your memory with false events; it's a problem some alcoholics have.

Both groups of subjects, the alcoholics and the controls, scored the same in the general cognitive test. But in the confabulation test, alcoholics performed worse. They also did worse in the sniffing tests. Alcoholics didn't have an impaired sense of smell overall; they could detect scents at the same threshold as non-alcoholics. But they had a harder time identifying odors and telling two odors apart. This indicates that the problem isn't in the actual smelling, but in the brain's processing of smells.

So although the researchers weren't able to confirm their observations with brain scans, it seems that alcoholics had impaired brain functioning specifically in the orbitofrontal cortex. In addition to causing confabulation, this affected their performance on a smell test.

If this relationship proves to be reliable, it could give doctors a shortcut to test their patients' mental functioning. A sniff test given to alcoholics could reveal how likely they are to be experiencing memory gaps. Smell tests given to patients with other psychiatric disorders that affect olfaction (such as depression, dementia, anorexia, or schizophrenia) could provide clues as to what cognitive problems they're having--or whether certain brain areas are working just fine. And in other patients, a poor smelling score could suggest an undiagnosed mental illness. Since this study found a result in odor processing in the brain, though, and not subjects' ability to detect odors generally, you don't have to worry that a head cold will get you sent to therapy.

For now, doctors will have to rely on probing questions and physical exams rather than scented pens. And no one knows what was going on with that kid in your kindergarten class who couldn't stop sniffing the grape Mr. Sketch marker--though if smell tests are introduced in doctor's offices, one assumes he'll be thrilled.

Maurage, P., Callot, C., Chang, B., Philippot, P., Rombaux, P., & de Timary, P. (2011). Olfactory Impairment Is Correlated with Confabulation in Alcoholism: Towards a Multimodal Testing of Orbitofrontal Cortex PLoS ONE, 6 (8) DOI: 10.1371/journal.pone.0023190

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