Functions and Circuits of REM Sleep

Abstract Ever since its discovery by Aserinsky and Kleitman in 1953, the quest to understand the function of rapid eye movement (REM) sleep has inspired researchers. Experimental evidence implicates both nonrapid eye movement (NREM) and REM sleep in learning and memory consolidation, although the underlying mechanisms remain unclear. It was suggested that REM sleep might provide a neural environment supporting processes essential to learning and cognition, including synaptic remodeling mechanisms such as long-term potentiation (LTP) and depotentiation or synaptic pruning of spines formed during previous wakefulness. Furthermore, the hypothesis “Sleep to remember, sleep to forget” posits that NREM sleep is important for the consolidation of newly formed memories, whereas the REM sleep state eliminates dispensable spines, thereby improving the signal-to-noise ratio in neural networks, the latter process often being referred to as an “unlearning” process that helps stabilize newly formed synapses and memories. In humans, REM sleep has frequently been associated with dreaming, which led to the hypothesis that REM sleep is important for the reactivation of emotional events that occurred during the previous waking period. Accordingly, the reactivation of brain regions linked to emotion regulation has been suggested to facilitate the consolidation of newly formed memories. Finally, the abundance of REM sleep during perinatal periods has supported the idea that REM sleep provides a context during which the development of neural circuits is facilitated.