There is no unifying theory to explain the experience of dreaming. Dreaming involves an altered state of consciousness that occurs during periods of REM (rapid eye movement) sleep. One of the most unusual features of this state is that most of the body's muscles are paralysed. The most common sleeping pattern is for a period of REM sleep to be preceded by four stages of non-REM sleep, and for this to repeat itself up to five times a night. Most adults and children, if woken during REM sleep, will report that they were dreaming. Whilst the physiological stages of sleeping may be similar across adults and young children, the potential complexity of a childs dreams develops as they age  alongside their imagination. Its difficult to prove that a dream is taking place  only after the fact can you know that you were dreaming. There are a small number of people, however, who do know when they are experiencing what is called a lucid dream. The scanning hypothesis posits that eyes move during REM sleep in accordance with the direction of gaze of ones dream. Research, for example with lucid dreamers, has shown that eyes do point towards the action that a dreamer, having a goal- orientated dream, describes.

Question: REM sleep periods always occur after four non-REM sleep periods.
Options:
A. true, B. false, C. uncertain
Answer: "B"