Phasic activities in the human body during REM sleep Part 2: Autonomic activity and general discussion

Numerous brief events, known as phasic activities, have been observed in terms of rapid eye movements (REMs), muscle activity, and autonomic nervous system activity during REM sleep. This occurs against the backdrop of sustained muscle atonia and vagal tone. The first part of this review was dedicated to REMs and skeletal muscle phasic activities. The second part, here, provides a list of phasic autonomic changes in the human body. Considerably stronger evidence exists for pupillary, respiratory, cardiovascular, and reproductive phasic activity than for gastrointestinal and urinary phasic activity. In addition to tonic miosis of the pupil, brief mydriasis occurs during REM sleep. The cardiovascular system exhibits phasic events such as spikes in blood pressure, tachycardia, and vasoconstriction alongside REMs. Phasic bradycardia episodes also occur during REM sleep without REMs. The respiratory system exhibits rapid and shallow breathing, as well as transient phasic hypoventilation, alongside REMs. The rate of spontaneous contractions in the esophagus and stomach increased during REM sleep compared to NREM sleep. In the reproductive system, phasic activity has been observed in the penis (although tonic activity is predominant), vagina and uterus during REM sleep. The review also examines how REMs, muscle twitches and autonomic phasic activities cluster together.