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To Sleep, Perchance to Synthesize Proteins

Sleep keeps neuroscientist Marcos Frank, PhD awake, studying the importance of slumber during early life when the brain is rapidly maturing and highly changeable. Building on his research showing that the brain during sleep is fundamentally different from the brain during wakefulness, Frank has found that cellular changes in the sleeping brain may promote the formation of memories. The world as the brain sees it. Optical ‘polar’ maps of the visual cortex. Credit: Marcos Frank, PhD
When an animal goes to sleep it's like a switch is thrown, he says, and everything is turned on that's necessary for making synaptic changes that form the basis of memories. The team used an animal model of cortical plasticity – the making and breaking of neural connections -- in response to visual cues. 

In studies over the past few years, the Frank lab has found that once the brain is triggered to reorganize its neural networks while awake, intra- and intercellular communication pathways engage, setting a series of enzymes into action within the reorganizing neurons during sleep.
 
In the newest study from the lab, published in the March 1 issue of Current Biology, the team has discovered new clues about how sleep consolidates brain plasticity based on previous visual cues.
 
Frank, an associate professor of Neuroscience at the Perelman School of Medicine at the University of Pennsylvania, found that sleep is associated with increased brain protein synthesis and transcription of messenger RNAs (mRNAs). Specifically, in the complicated process of protein synthesis, transcription of the genetic message in mRNAs occurs in response to waking, but translation of the code in mRNAs into the final protein structure requires sleep. This synthesis, in turn, is critical for making long-term memories.  

The team showed that inhibition of protein synthesis that is dependent on the molecular complex called mTOR1 during sleep impairs sleep-dependent formation of nerve-cell connections, but has no effect on plasticity induced during wakefulness.
 
These findings show that sleep promotes mRNA translation. Interruption of this process has consequences for the function of an animal because it abolishes the consolidation of experience in the cortex of the brain during sleep.

According to Frank, this suggests that the reason sleep loss affects our memories and our ability to think is because vital brain proteins are not being synthesized. Future studies designed to identify these proteins -- and their functions -- will provide key insights into the mystery of sleep function, and what that holds for better sleep hygeine and combating chronic physiogical costs of sleep problems.

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ResearchBlogging.org Seibt, J., Dumoulin, M., Aton, S., Coleman, T., Watson, A., Naidoo, N., & Frank, M. (2012). Protein Synthesis during Sleep Consolidates Cortical Plasticity In Vivo Current Biology DOI: 10.1016/j.cub.2012.02.016

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