We're all familiar with the feeling—waking up from a restless night only to realize that this will be a very long, sleepy day. Recent research reveals that honeybees are also sensitive to sleep deprivation, and although a cup of coffee may give you a morning buzz, the bees aren't so lucky.
Neurobiologists at the Free University of Berlin have found that sleepy bees fail to remember lessons learned the day before, a finding that could help scientists discover the neural processes involved in sleep and memory formation. They present their research October 25 in the Journal of Experimental Biology.
"We started with the idea that we could look for a neural substrate of learning and memory in bees, since they have a wonderful memory, can be easily trained, and we know their brain well at the neuronal level," says study co-author Randolf Menzel.
After characterizing how honeybees find their way home when released in a new location, the scientists captured and then released bees in unfamiliar territory some 600 meters from their hive. In addition to tracking how long the bees needed to return home, the researchers monitored bee sleep. Bees take brief naps throughout the day in addition to longer periods of nocturnal sleep. (Snoozing bees are easy to spot because their antennae droop.) The scientists made their observations both by watching bees in person and by tracking their activity via radio-frequency devices that they glued onto some of the insects.
The researchers verified first that finding a new route home did not alter other foraging behaviors, although it did lead to an increase in sleeping time in the first part of the night. Curious as to whether this change might reflect some learning or memory process, the team decided to see what happens when bee slumber is disturbed by selectively placing the insects in a box that was gently agitated for about eight hours, making it difficult for them to relax and get a good night's sleep.
The next day the researchers found that sleepless bees and well-rested ones performed no differently when left to find their way home from a novel location. In other words, lack of sleep apparently did not inhibit the bees' learning processes. "This suggests that there are forms of learning that seem to be totally independent of sleep," Menzel says.
The scientists observed, however, a significant and obvious difference when bees were brought to the new spot for a second day. This time, bees that had slept well found their way home faster and fewer got lost along the way than on the previous day. That observation indicates that the well-rested bees had learned from their experience the day before. Drowsy bees, however, took about as long to return home on the second day as on the first, and were just as likely to get lost.
The authors conclude that without sleep, the bees' brains could not properly consolidate memories from the night before. If they are correct, the finding adds to growing evidence from a number of human and animal studies that sleep plays an important role in memory and learning.
Some researchers not involved in this research believe more studies are needed to clarify the finding. "We all do tasks more poorly, especially recently learned tasks, after sleep deprivation but may be able to perform them properly after getting sleep at a subsequent time. In other words, consolidated memories may not be accessed in sleepy animals," says Jerome Siegel at the University of California, Los Angeles. Siegel is concerned that additional measurements are needed to distinguish between memory and task performance.
Nevertheless, the study is still an important step. Jan Born a neuroendocrinologist, at the University of Lübeck in Germany, praises the research, "I think this is a very valuable finding for the whole field—it shows the formation of memories is hampered when bees do not sleep or rest."
Born adds that the finding supports the principle that complex memories need some kind of off-line processing—such as sleep—to form. "The simpler the brain is," Born says, "the easier it will be to find the mechanisms of this consolidation process."