Do people lose their senses of smell and taste as they age?

N. Sly, Windsor, Australia

Charles J. Wysocki, a neuroscientist at the Monell Chemical Senses Center in Philadelphia who studies variation among individuals in the perception of odors and the response of the human nose to chemical irritation, explains:

IT IS TRUE THAT as people age they often complain about decreases—or even losses—in their ability to taste a superb meal or a fine beverage. When people eat, however, they often confuse or combine information from the tongue and mouth (the sense of taste, which uses three nerves to send information to the brain) with what is happening in the nose (the sense of smell, which uses a different nerve input).

It is easy to demonstrate this confusion. Hold a handful of jellybeans of different flavors and close your eyes. With your other hand, pinch your nose closed. Now pop one of the jellybeans into your mouth and chew, without letting go of your nose. Can you tell what flavor went into your mouth? Probably not, but you most likely experienced the sweetness of the jellybean. Now let go of your nose. Voilà—the flavor appears.

This phenomenon occurs because smell provides most of the information about the flavor. Chemicals from the jellybean, called odorants, are inhaled through the mouth and exhaled through the nose, where they interact with special receptor cells that provide information about smell. These odorants then interact with the receptor cells and initiate a series of events that are interpreted by the brain as a smell.

Estimates for the number of odorant molecules vary, but they most likely number in the tens of thousands. Taste, on the other hand, is limited to sensations of sweet, sour, bitter, salty and umami (or savory—the taste of monosodium glutamate, or MSG).

With advancing age, the sense of smell diminishes—much more so than the decrease in sensitivity to tastes. This decrease may result from an accumulated loss of sensory cells in the nose (perhaps as much as two thirds of the original population of 10 million).

How long can humans stay awake?

Samuel, Honolulu, Hawaii

The late J. Christian Gillin of the San Diego Veteran Affairs Healthcare Center and professor of psychiatry at the University of California, San Diego, conducted research on sleep, chronobiology and mood disorders. He had supplied this response:

THE QUICK ANSWER is 264 hours, or 11 days. In 1965 Randy Gardner, a 17-year-old high school student, set this apparent world record for a science fair. Several other research subjects have remained awake for eight to 10 days. All showed progressive and significant deficits in concentration, motivation, perception and other higher mental processes. Nevertheless, all recovered to relative normalcy with one or two nights of sleep.

The more complete answer to this question revolves around the definition of “awake.” Prolonged sleep deprivation in normal subjects induces numerous brief episodes of light sleep (a few seconds), often described as “microsleep,” alternating with drowsy wakefulness, as well as loss of cognitive and motor functions. Gardner was “awake” but basically cognitively dysfunctional at the end of his ordeal.

In certain cases of rare human medical disorders, the question of how long people can remain awake raises surprising answers—and more questions. Morvan’s syndrome, for example, is characterized by muscle twitching, pain, excessive sweating, weight loss, periodic hallucinations and sleeplessness. In 1974 neurobiologist Michel Jouvet and his colleagues in Lyon, France, reported on a 27-year-old man with this disorder and found he had virtually no sleep over a period of several months. During that time the man did not feel sleepy or tired and did not show any disorders of mood, memory or anxiety. Nevertheless, nearly every day between 9 and 11 p.m., he experienced 20 to 60 minutes of auditory, visual, olfactory and somesthetic (relating to the sense of touch) hallucinations, as well as pain and blood vessel constriction in his fingers and toes.

The ultimate answer remains unclear. Will bioengineering eventually produce soldiers and citizens with a variant of Morvan’s syndrome, who need no sleep yet remain effective? I hope not. A good night’s sleep is one of life’s blessings. As Coleridge wrote in The Rime of the Ancient Mariner, “Oh sleep! It is a gentle thing, beloved from pole to pole!”

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