The Sentinel Sleep Theory: Unweaving The Biological Function of REM Sleep

The biological function of rapid eye movement (or REM) sleep—one of the great mysteries of neuroscience—remains unknown. Here, I demonstrate that the biological function of REM sleep is to heighten brain alertness, significantly reducing the high vulnerability of deep sleep. Every organism with a nervous system must undergo deep sleep: a necessity that comes with substantial vulnerability. Deep sleep, by lowering alertness, compromises the organism's safety, putting its survival at risk. Therefore, REM sleep is a necessary adaptation for any organism that must sleep. My primary goal here is to present a comprehensive conceptual framework—supported by extensive empirical evidence—to connect numerous disparate empirical findings under a unified theory of the biological function of REM sleep. Additionally, I also provide a historical narrative to explain its origin and subsequent evolution. To test the theory I developed here, I drew on a substantial body of evidence and testable hypotheses derived from it. All 38 hypotheses capable of empirical verification were corroborated, revealing that the theory is widely corroborated. Furthermore, it also resisted numerous other attempts at refutation. Thus, the theory I elaborated here will advance theoretical neuroscience and change the way REM sleep research is planned and carried out.