Eyes on the Brain

A neurobiologist explores the amazing capacity of the brain to rewire itself at any age

There’s No Accounting for Taste

Who’s got good taste?

So you think you have better taste than a fly? A few years ago, my students and I did an experiment to find out. We gave flies a choice of plain water versus water with a very dilute sugar solution. The flies always chose the sugar solution, and we watched each one extend its long proboscis into the drink. The sugar solution was so dilute, however, that we couldn't taste the sweetness at all. Does that mean that flies have superior taste? I think that's the wrong question. Since we are large, warm-blooded animals, we need to consume a lot of calories. If we could taste the very dilute sugar water, we would be tempted to drink it, yet it would not give us enough calories to survive. A tiny, cold-blooded fly, however, can make do with such a small amount of sugar.

We followed these observations with another taste experiment. We painted our tongues with blue food dye so that the papillae, the little bumps on our tongue that house our taste buds, stood out against the blue-stained surface of the tongue. Then, using a magnifying glass, we counted the number of papillae in a given area of each person's tongue. We also filled out a survey examining what foods we did or did not like and looked to see if there was any correlation between the number of papillae (and therefore taste buds) and our food preferences.

For the most part, we didn't see any correlations, and this made sense. What we like to eat depends not only on how many and what type of taste receptors we have but also on how that information is integrated and processed with other sensory information in the brain. My daughter, for example, has an exceptionally good sense of smell which makes her a very picky eater. The way the food feels in our mouth (think of oysters) may influence whether or not we like it, as does our culture, our experiences, and emotional associations. I was given jell-o after my third eye operation at age 7. Since I had been anesthetized with ether (this was 1961) , I felt horribly nauseated after the surgery, and an association was made. To this day, I can't stomach jell-o.

There was however one really interesting result from our food survey experiment. Although most students had roughly the same number of papillae on their tongue, one student had about ten-fold less and another three times more. The student with very few papillae ate everything. She had no strong likes or dislikes. In contrast, the student with the unusually large number of papillae hardly liked anything at all, and what she did like was very bland. If we are hypersensitive to tastes, we might reject everything and become malnourished, but if we aren't sensitive enough, we won't discriminate edible substances from bitter-tasting poisons. As with the flies, our sensitivities are tailored to what we need to detect to survive.

 

Susan R. Barry, Ph.D., is a professor of neurobiology in the Department of Biological Sciences at Mount Holyoke College and the author of Fixing My Gaze (June, 2009).

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