Due to their reputation as vectors for Brettanomyces and their unwelcome presence when discovered swimming in one’s glass, fruit flies have long been viewed as annoying pests by wine drinkers. But as research subjects, they’re surprisingly beneficial: Their brains are teaching us more about how we humans learn to differentiate aromas.

Working in collaboration with the Salk Institute for Biological Studies in La Jolla, California, researchers studying fruit flies at Cold Spring Harbor Laboratory (CSHL) in Cold Spring Harbor, New York, have discovered two different types of olfactory neurons attached to the business end of our odor receptor cells: reliable olfactory neurons, which consistently identify odors, and unreliable neurons, which respond to odors unpredictably over time and “learn” to distinguish nuanced odors through experience.

Of our sensory systems (vision, olfaction, taste, hearing, and balance), olfaction is one of the oldest. Our olfactory neurons, which our bodies have the capacity to regenerate, are directly connected to
the olfactory bulb, which relays impulses to other brain regions like the somatosensory cortex. The random way unreliable neurons respond originates from circuits deep within the brain—a scenario
that, according to researchers, suggests they serve a significant purpose.

The study, conducted by CSHL associate professor Saket Navlakha and Salk Institute researcher Shyam Srinivasan, is based on research that was done years ago by former CSHL assistant professor Glenn Turner, who noticed during trials that some of the olfactory neurons of fruit flies fired consistently while others varied. At the time, those differences were dismissed as background noise and didn’t warrant further investigation.

In 2022, Navlakha and Srinivasan decided to take another look, and their research, which also employed fruit flies, identified the origin and purpose of the variability. As part of the study, the team isolated a small group of reliable neurons that responded the same to similar odors and, as a result, help the fruit flies quickly discern different smells. They also isolated a much larger group of unreliable neurons that respond less predictably when detecting similar smells.

These are the neurons that help flies—and us, for that matter—to identify nuanced aromas in, for example, wine as well as to discern novel odors and group them together. The flies’ aversion to unfamiliar odors can be predicted based on the activity of the neurons those odors induce. (You might question how research done on fruit flies could apply to humans. While the humannose of course differs from that of a fruit fly, not to mention those of other mammals, at the microanatomical level our olfactory systems are essentially the same.)

While these neurons are useful, the researchers point out that they require many repeated exposures to take full advantage of their ability to “learn.” This news won’t come as a surprise to those
students of wine whose mantra is “taste, taste, taste” when it comes to mastering sensory analysis.

The results of this study could help explain how, through our unreliable neurons, we learn to differentiate between similarities detected by other senses such as taste, sight, and hearing and how we respond based on those sensory inputs—much like the process of transduction, in which our neurons convert aroma and taste compounds into electrochemical signals that our brains can perceive.