Rapid eye movement (REM) sleep is physiologically different from the other phases of sleep. Most of the postulations by researchers have speculated on the role or significance of the REM sleep stage. Most of the proposed roles that are attributed to REM sleep in vital brain functions are still mere speculations. For example, there is no clear evidence to suggest that REM sleep may play a particular role or may mediate a proposed mechanism for a specific brain function. The aim of this review is to identify those vital processes in brain function believed to be REM sleep driven and which have featured prominently in the works of researchers in the past. The method adopted in this review was that of information gathering from sources which included published works of past and present researchers, articles on sleep presented in seminars and conferences, published articles on sleep, lecture notes on sleep physiology, textbooks of current editions in neuroscience, reports and published works accessed from the Internet using search engines such as Google, Mamma, PubMed etc. The postulations and hypothesized roles of REM sleep in vital brain function have been clearly highlighted in this review. It is concluded from this review that neural factors involved in the central mechanisms of REM sleep in vital brain function have been clearly highlighted in this review. It is concluded from this review that neural factors involved in the central mechanisms of REM sleep are not fully understood. Nevertheless, information noted in this review lends further credence to the notion that REM sleep is crucial and probably the most important sleep phase. It is hoped that facts in the proposals and postulations chronicled in this review will serve as important information source for neuroscientists and different researchers engaged in the subject of sleep.