Study shows evidence that the brain is reset during periods of sleep

A study has shown that proteins located in the specialized parts of neurons that enable brain cells to communicate with other neurons build up in the brains of sleep-deprived fruit flies and drop to reduced levels in the brains of well-rested flies. This, suggests researchers from the Center for Sleep and Consciousness at the University of Wisconsin-Madison School of Medicine and Public Health, adds evidence to their theory of "synaptic homeostasis."

As the researchers explain, the theory behind synaptic homeostasis is that synapses grow stronger when we are awake, as we learn and adapt to an evolving environment. When we go to sleep, those synapses are brought to a lower level of strength, which essentially refreshes our brain. "We know that sleep is necessary for our brain to function properly, to learn new things every day, and also, in some cases, to consolidate the memory of what we learned during the day," says Chiara Cirelli, associate professor of psychiatry and member of the research team. "During sleep, we think that most, if not all, synapses are downscaled: at the end of sleep, the strongest synapses shrink, while the weakest synapses may even disappear."

To conduct their study, the sleep researchers devised an innovative technique involving a "fly agitator" to keep the flies awake. The agitator was designed with 10 plates, each of which contained 32 flies. Over a period of 24 hours, a robotic arm shook the plates occasionally to prevent the flies from dozing off. After dissecting their brains, the scientists measured the levels of four pre-synaptic proteins and one post-synaptic protein using three-dimensional photos generated by confocal microscopy. In the photos, the brains of the sleep-deprived fruit flies are shown to be filled with a synaptic protein called Bruchpilot (BRP), which helps transport messages in the synapses between neurons. Conversely, in the brains of the well-rested flies, levels of five synaptic proteins, including BRP, were shown to have dropped by 30 to 40 percent during sleep. The researchers believe this is evidence that by allowing synaptic downscaling, sleep clears away larger synapses that consumer space and energy - what they call unnecessary "noise" - from the previous day, essentially resetting the brain to allow more growth and learning the next day.

 News Release: Sleep: Spring cleaning for the brain? www.eurekalert.org    April 2, 2009