Brain Temperatures, Activation Patterns, and Dreaming

Abstract

This chapter demonstrates exactly how well the adaptive inactivity theory of sleep explains several unusual features of human sleep, which were not fully known and understood before the publication in 2015 of a longitudinal study of sleep in three indigenous societies without electricity. These indigenous groups sleep on average only 5–7 hours a night, and they sleep longer in the winter than in the summer by almost an hour. Unlike other primates, the human sleep cycle is linked to the temperature cycle, not the light–dark cycle. The findings in this field study are then linked to laboratory studies of cerebral blood flow during human sleep, which in turn are consistent with the activation patterns during the sleep-onset process, rapid eye movement (REM) sleep, and early morning NREM 2 sleep. This work sets the stage for showing that dream reports after NREM 2 awakenings are increasingly frequent and are similar in content to those from REM sleep by the time of the morning awakening. When combined with the findings in Chapter 5 on dreaming during the sleep-onset process, this chapter again shows that dreaming occurs when the imagination network is active and other neurocognitive networks are not.