Midbrain reticular activating system (RAS) stimulation causes wakefulness by generalized activation of the various brain tissues, such as cerebral cortex, thalamus, basal ganglia, brainstem and spinal cord.
During sleep we experience two patterns of sleep namely non- REM sleep (randomised eye movement) and REM sleep, which follow one another in episodes. The RAS is responsible for producing NREM sleep.
Thus, the blanks can be filled with reticular activating system; non- REM sleep.