If you've ever been sleep-deprived, you know the feeling that your brain is full of wool. Now, a study published in the April 3 edition of the journal Science has molecular and structural evidence of that woolly feeling - proteins that build up in the brains of sleep-deprived fruit flies and drop to lower levels in the brains of the well-rested. The proteins are located in the synapses, those specialized parts of neurons that allow brain cells to communicate with other neurons.

Sleep researchers at the University of Wisconsin-Madison School of Medicine and Public Health believe it is more evidence for their theory of "synaptic homeostasis." This is the idea that synapses grow stronger when we're awake as we learn and adapt to an ever-changing the environment, that sleep refreshes the brain by bringing synapses back to a lower level of strength. This is important because larger synapses consume a lot of energy, occupy more space and require more supplies, including the proteins examined in this study.

Sleep - by allowing synaptic downscaling - saves energy, space and material, and clears away unnecessary "noise" from the previous day, the researchers believe. The fresh brain is then ready to learn again in the morning.

The researchers - Giorgio Gilestro, Giulio Tononi and Chiara Cirelli, of the Center for Sleep and Consciousness - found that levels of proteins that carry messages in the synapses (or junctions) between neurons drop by 30 to 40 percent during sleep…