Cortical circuit activity underlying sleep slow oscillations and spindles

Significance Slow oscillations and spindles are hallmarks of the EEG during slow-wave sleep. They are thought to support memory consolidation, particularly in instances where the faster spindle nests into the “upstate” of a slow oscillation. Using two-photon and wide-field imaging, we recorded calcium transients from distinct populations of cortical excitatory and inhibitory neurons during sleep in mice. Compared with spindles or slow oscillations occurring in isolation, events where spindles nested in a slow oscillation upstate were indeed accompanied by a unique pattern of calcium activity where high pyramidal cell activity appears to concur with high perisomatic inhibition through parvalbumin-positive interneurons and with low dendritic inhibition through somatostatin-positive interneurons. These conditions might foster dendritic plasticity.