Non-rapid eye movement (NREM) sleep provides recovery through cortical slow oscillations that enable synaptic plasticity and cellular maintenance, while rapid eye movement (REM) sleep performs a selection process to identify networks that have achieved sufficient recovery.

We propose that NREM and REM sleep have distinct and complementary contributions to the overall function of sleep. Specifically, we suggest that cortical slow oscillations, occurring within specific functionally interconnected neuronal networks during NREM sleep, enable information processing, synaptic plasticity, and prophylactic cellular maintenance (“recovery process”). In turn, periodic excursions into an activated brain state—REM sleep—appear to be ideally placed to perform “selection” of brain networks, which have benefited from the process of “recovery,” based on their offline performance.