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Tuesday, March 22, 2016

Sleep suppresses brain rebalancing




Why humans and other animals sleep is one of the remaining deep mysteries of physiology. One prominent theory in neuroscience is that sleep is when the brain replays memories "offline" to better encode them ("memory consolidation").
A prominent and competing theory is that sleep is important for re-balancing activity in brain networks that have been perturbed during learning while awake. Such "rebalancing" of brain activity involves homeostatic plasticity mechanisms that were first discovered at Brandeis University, and have been thoroughly studied by a number of Brandeis labs including the lab of Brandeis professor of biology Gina Turrigiano.
Now, a study from the lab just published in the journal Cell shows that these homeostatic mechanisms are indeed gated by sleep and wake, but in the opposite direction from that theorized previously: homeostatic brain rebalancing occurs exclusively when animals are awake, and is suppressed by sleep.
These findings raise the intriguing possibility that different forms of brain plasticity - for example those involved in memory consolidation and those involved in homeostatic rebalancing - must be temporally segregated from each other to prevent interference.
The requirement that neurons carefully maintain an average firing rate, much like the thermostat in a house senses and maintains temperature, has long been suggested by computational work. Without homeostatic ("thermostat-like") control of firing rates,