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Giulio Tononi: 2011 Allen Institute for Brain Science Symposium

Giulio Tononi, University of Wisconsin, Madison “Sleep function and synaptic homeostasis”

We spend a third of our lives in sleep, but we have no idea why. This, according to Dr. Tononi, “is most embarrassing for neuroscience.” Slow sleep oscillations — traveling waves — propagate throughout the brain on the superhighways of the connectome, then they spread out through the rest of the brain; this happens a thousand times every night, but we have no idea why. Dr. Tononi proposed a theory for why we sleep, which basically states that “sleep is the price we pay for synaptic plasticity.” That is, sleep exists as a sort of “offline” reset, or release valve, to renormalize synaptic strength that steadily increases during wakefulness. Dubbed the Synaptic Homeostasis Hypothesis (SHY), Tononi presented supportive evidence from a variety of perspectives including molecular, electrophysiological, and anatomical.

A correlative basis for SHY is the observation that genes involved in plasticity drop during sleep and a validating piece of evidence would lie in the ability to view the increase in synaptic potentiation in the sleep cycle. If validated, Dr. Tononi pointed to functional consequences of SHY that fall in a cycle such that 1) net synaptic potentiation in wakefuleness has energy, space, supply cost, and saturates learning until 2) renormalization during sleep restores the brain and consolidates and integrates memories.

Theory: Sleep re-normalizes the brain.

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