Sleep and learning studies suggest that memory consolidation following learning requires processes selectively active during rapid eye movement (REM) sleep. However, the mechanism(s) responsible for the activation of these processes remain largely unknown. To explain part of this mechanism, this article reviews findings of recent studies that were designed specifically to explain how activation of the phasic pontine-wave (P-wave) generator is involved in memory processing during the post-training REM sleep period. This review begins with the oldest concept of conscious state-dependent memory processing and ends with a possible mechanism of how activation of the brainstem P-wave generator regulates neuronal activation-dependent gene expression and protein synthesis.