Fundamental questions related to sleep such as “Why is sleep essential?” and “How are dreams generated?” remain unsolved. We recently identified a brainstem circuit that operates as the central switch that induces REM sleep in mice (ref. 1). This allowed us to generate mice in which REM sleep can be increased or decreased at a desired time point, and to identify circuits that control forebrain activity during REM sleep. In addition, based on imaging approaches focusing on cerebral blood flow, we found that REM sleep is characterized by extremely high cerebral capillary blood flow, suggesting a crucial role for REM sleep in brain maintenance (ref. 2).

Considering that all animals investigated so far exhibit sleep, sleep might serve a highly conserved basic role. Based on an unbiased screening using the worm C. elegans, we found that endoplasmic reticulum (ER) factors that are involved in protein quality control strongly affect sleep amount, both in worms and mice (ref. 3). I will discuss the possibility that sleep evolved to cope with ER stress.

1. Kashiwagi et al. A pontine-medullary loop crucial for REM sleep and its deficit in Parkinson’s disease. Cell 187(22):6272 (2024). DOI:10.1016/j.cell.2024.08.046

2. Tsai et al. Cerebral capillary blood flow upsurge during REM sleep is mediated by A2A receptors. Cell Reports 17:109558 (2021). DOI:10.1016/j.celrep.2021.109558.

3. Kawano et al. ER proteostasis regulators cell-non-autonomously control sleep. Cell Reports 42(3):112267 (2023). DOI:10.1016/j.celrep.2023.112267