Sleep promotes branch-specific formation of dendritic spines after learning

To sleep, perchance to remember Many researchers believe sleep helps us consolidate our memories, but no one knows quite how. Yang et al. investigated the precise role of sleep in changing mouse brain structures (see the Perspective by Euston and Steenland). When mice learned motor tasks, small protuberances—or “spines”—formed on some of the dendritic branches of specific brain neurons. These spines represent the physical correlate of a memory. But the neurons grew and retained these spines better when the mice slept after learning the task. Neurons that fired during learning fired again during subsequent slow-wave sleep, allowing the mice to conserve the newly formed spines—and memories. Science, this issue p. 1173; see also p. 1087 In mice, synaptic connectivity changes after motor learning are influenced by sleep. [Also see Perspective by Euston and Steenland] How sleep helps learning and memory remains unknown. We report in mouse motor cortex that sleep after motor learning promotes the formation of postsynaptic dendritic spines on a subset of branches of individual layer V pyramidal neurons. New spines are formed on different sets of dendritic branches in response to different learning tasks and are protected from being eliminated when multiple tasks are learned. Neurons activated during learning of a motor task are reactivated during subsequent non–rapid eye movement sleep, and disrupting this neuronal reactivation prevents branch-specific spine formation. These findings indicate that sleep has a key role in promoting learning-dependent synapse formation and maintenance on selected dendritic branches, which contribute to memory storage.