Beyond down-regulating cortical activity, sleep also promotes long-term memory formation and the strengthening of synaptic connections. It is possible that both core sleep stages, slow-wave sleep (SWS) and rapid eye movement (REM) sleep, contribute to these processes. Niethard et al. used in vivo two-photon calcium imaging in mice to assess the activity of large populations of cortical layer 2/3 cells during SWS and REM sleep. Most pyramidal neurons substantially decreased their activity during SWS and REM sleep episodes. The decrease during SWS sleep, but not during REM sleep, was accompanied by increased inhibitory interneuron activity. However, a subpopulation of pyramidal cells exhibited upregulated activity during SWS. These neurons are possibly involved in memory formation, and also underwent profound down-regulation during subsequent REM sleep.
J. Neurosci., 41, 4212 (2021).