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How the brain tidies up memories during sleep

last modified Mar 20, 2018 04:03 PM
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".

 

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During the day neuronal connections in the brain are created and strengthened as we interact with our environment. New information, concepts and memories are encoded in those dynamic neuronal connections. While brains have an immense storage capacity, the continuous bombardment of sensory inputs during the day and the high energetic cost of storing information make it intuitively obvious that there have to be certain rules dictating which information is relevant enough to be stored and which will be ignored or forgotten. In this issue, González-Rueda et al., show that this could occur during sleep. Using in vivo electrophysiology and optical stimulation in mice, González-Rueda et al., found that the specific brain activity that occurs during slow-wave-sleep promotes the weakening of unimportant connections while maintaining the strongest synaptic weights of connections encoding essential information. The drawing shows an intricate neuronal network of an awake mouse (left) and the same network following sleep-mediated input-specific synaptic pruning (right). Artwork by Hugo González-Rueda.


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.

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