Fig. 6. Time spent in wakefulness (W), non–rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep after injection of saline (  A ), morphine (  B ), neostigmine (  C ), or carbachol (  D ) into the medial pontine reticular formation. These plots represent the minute-by-minute scoring of polygraphically confirmed states of arousal. Note the enhancement of REM sleep caused by neostigmine or carbachol, and the inhibition of REM sleep caused by morphine. These data are consistent with the interpretation that the decrease in REM sleep caused by systemically administered opioids is mediated, at least in part, at the level of the mPRF. From Kshatri  et al. ;  used with permission.