Can you tell if a fly is asleep? This is precisely the question asked seven years ago by Dr. Joan Hendricks, who is now the Dean of the School of Veterinary Medicine at the University of Pennsylvania. In collaboration with Dr. Amita Sehgal and Dr. Allan Pack of the Penn Center for Sleep and Respiratory Neurobiology (CSRN), Dr. Hendricks wanted to determine if the fruit fly Drosophila melanogaster, an animal used since the early 1900s for genetic studies in biology, has a sleeplike state much as we do. But unlike human studies, where one can measure brain electrical activity to distinguish sleep from the waking state, one cannot easily measure fly brain waves. Instead, Dr. Hendricks used behavioral measures.
It was already known that Drosophila are not active all day, but rather have rest and activity patterns that follow an approximately 24-hour, or circadian, rhythm. They are active during the day and inactive at night, just like us. To determine if the inactive period corresponded to fly sleep, or simply to restful wakefulness, Dr. Hendricks first asked if the flies were less responsive during this period, much as we are less likely to respond to stimuli when asleep. She found that indeed, the flies were less likely to move in response to a gentle tap during these nocturnal quiescent periods than during the day.
