How the brain tidies up memories during sleep

Connections between brain cells are refined during sleep in a way that makes a memory stand out without interfering with previously stored memories, new study by Ole Paulsen's group shows

A new study published in Neuron sheds new lights on the underlining mechanisms of memory maintenance during sleep.

"It has been suggested for a long time that sleep helps reinforcing memories within the brain, but the actual mechanisms were not clear" says Ana González-Rueda, former PhD student at Ole Paulsen's lab. During the waking hours, as we interact with the world and learn, the brain absorbs information and connections between neurons are spontaneously formed or modified to create the basis of memories. "Since we are exposed to new information constantly, our brain would be overloaded if it kept all of these newly formed connections" says Dr. González-Rueda.

By measuring the synaptic activity in anesthetized mice that replicate the sleeping brain, the team has discovered that only the strongest connections that are formed during the day are maintained during the sleep. "We found that during slow-wave sleep, when groups of neurons are reactivated in a similar way as they did at wake, the coincidence of neuronal activity promotes the refinement of neuronal connections enabling more efficient storage of important information and the elimination of irrelevant connections" says Dr. González-Rueda. "Effectively, the brain is 'tidying up' during sleep, discarding the weaker connections to ensure strong memories are consolidated instead".

Reference: Ana Gonzalez-Rueda, Victor Pedrosa, Rachael C. Feord, Claudia Clopath, Ole Paulsen (2018), Activity Dependent Downscaling of Subthreshold Synaptic Inputs during Slow-Wave-Sleep-like Activity In Vivo, Neuron, 97, 1-9.