Theories attempting to explain the origin and functions of REM sleep include: (1) that REM sleep provides stimulation for the development of the brain; (2) that it performs a chemical restoration function, since during REM dreaming neuro-protein synthesis occurs along with the restoration of other depleted brain chemicals; (3) that it provides oculomotor (eye movement) coordination, since during non-REM sleep the eyes move independently of each other; (4) that it provides a vigilance function, since REM sleep (stage I) is characterized by ....