Upon discovery, rapid-eye-movement sleep (REMs) was met with curiosity regarding its function due to its association with dreaming and the seemingly paradoxical occurrence of ‘wake-like’ eye and brain activity during sleeping behavior. Six decades later, a substantial body of evidence linking REMs to memory formation has been described (Rasch and Born, 2013). In humans, increased REM amounts have been reported following procedural memory tasks, as well as declarative memory tasks incorporating complex or emotionally relevant material. Furthermore, depriving REMs after learning of such tasks produced memory deficits. Similar findings have been described in rodents using tasks such as the Morris water maze and active or passive avoidance (Abel et al, 2013).

Despite the cumulative body of evidence, the debate surrounding the role of REMs in memory formation has persisted for some time (Rasch and Born, 2013; Siegel, 2001). This has been due to the difficulty in experimentally isolating REMs, which occurs in multiple episodes of varying (seconds to minutes) duration throughout sleep interposed by periods of non-REMs (NREMs). Thus, traditional pharmacological techniques are not temporally precise enough to selectively target REMs. Additionally, as REMs is an integral component of mammalian sleep, selective REM deprivation inevitably results in physiological changes, such as increased metabolic hormone levels, making interpretation of data obtained difficult. Correlative approaches avoid these issues but cannot prove a direct relationship (Rasch and Born, 2013).

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