Because vibrations lead to sleepiness

It is common practice to put babies to sleep. Children and adults also feel sleepy during long car journeys. There is something about the delicate mechanical stimuli that makes humans of all ages sleepy. Sleeping in fruit flies is very similar to human sleep, and you can learn a lot about human sleep by studying how flies sleep is regulated. In a research published in Cell reports On December 1, 2020, researchers report that flies fall asleep during vibration through a simple form of learning called habituation.

“Babies like to be lulled to sleep, but the neural mechanisms underlying this well-known phenomenon remain largely a mystery. We wanted to establish the fruit fly as a model system for studying sleep induction mechanisms by mechanical stimulation,” he says. Kyunghee Koh, Ph.D., associate professor of neuroscience at the Vickie & Jack Farber Institute for Neurosciences and the Synaptic Biology Center at Thomas Jefferson University and senior author of the study.

The researchers found that flies sleep longer during vibration and are less responsive to light pulses that would otherwise wake them. Also, they are more awake after the vibration, which suggests they have accumulated “sleep credit”. In other words, they behave as if they sleep more than they need to while vibrating, which allows them to function well with less sleep later on.

These findings suggest that vibration-induced sleep is similar to regular sleep and serves some of their vital functions. They found that the amount of extra sleep that flies get while vibrating depends on the genetic background of the flies, as well as the frequency and amplitude of the vibration. Dr. Koh’s group also learned that multiple sensory organs are involved in the process.

Interestingly, the vibration initially makes the flies more active than usual, but gradually causes them to fall asleep. Furthermore, the ability to fall asleep improves when exposure to vibrations is repeated multiple times, implying habituation, a form of simple learning. “Flies learn over time that the vibration is not threatening, which reduces their reaction to stimulation that would otherwise make them alert,” says Dr. Koh. Suppression of alertness seems necessary for vibration-induced sleep because the mutant flies with increased dopamine levels which make them more alert not fall asleep with vibrations.

It is not yet clear whether similar mechanisms are at work in humans. But Dr. Koh says, “Further investigation can help us develop and optimize sensory stimulation as a sleep aid for humans. Our results suggest that it would be worth customizing the stimulus parameters for each individual in different sessions.”

However, his team’s initial goals are to learn more about the underlying neural mechanisms by using the fruit fly as a model system. They plan to identify specific neurons in the fly’s brain involved in the process and determine whether vibration-induced sleep works like normal sleep to improve memory and longevity and whether repetitive stimulation of other senses (eg, sight and smell) can also induce sleep.