In recent years, several laboratories succeeded in applying imaging approaches such as calcium imaging and structural two-photon imaging to naturally sleeping animals. These approaches are promising as they allow the direct investigation of how sleep affects the brain's connectivity at the level of specific synapses as well as in larger networks comprising hundreds of neurons. Functional calcium imaging of brain circuits during natural sleep now allows cell type specific tracking of cellular calcium activity, which is one key element in the regulation of neuronal plasticity in different types of neurons. By using specific transgenic mouse lines, not only sleep specific changes in excitation but also changes in inhibitory activity can be differentiated. Furthermore, in combination with electrophysiological recordings, these imaging methods allow investigating which kind of circuit activity underlies distinct sleep-stage specific oscillations. At the level of specific synapses, structural imaging approaches have provided first evidence that slow wave sleep and REM sleep differentially modulate dendritic spine turnover.
However, despite these technical advances, it is still not well understood how sleep affects neuronal plasticity in different brain areas, how this relates to behavior and in particular memory consolidation, and how these memory forming process are linked to the global homeostatic regulation of synaptic connectivity during sleep. This symposium is focused on discussing and integrating new experimental findings related to an evolving understanding of how sleep affects brain plasticity by using functional and structural in vivo imaging techniques of neuronal circuits in rodents. The symposium will include five talks, all focusing on studies using in-vivo imaging during sleep, but covering different aspects of sleep and plasticity.

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