Introduction to Psychology 10th Edition by Rod Plotnik,Haig Kouyoumdjian

Exercise 29

During a night's sleep, we gradually pass through five stages. Stage 1, which is a transition between waking and sleeping, has brain waves known as (a) _____Stage 2 has brain waves with bursts of activity that are called (b) _____Stage 3 and especially stage 4 are marked by high-amplitude, low-frequency (c) _____Stage 4 is often considered the deepest stage of sleep because it is the most difficult from which to be awakened. During stage 4, heart rate, respiration, temperature, and blood flow to the brain are (d) _____Together, stages 1, 2, 3, and 4 are referred to as (e) _____, in which we spend about 80% of our sleep time. About five or six times throughout the night, we enter a paradoxical state called (f) _____, which accounts for the remaining 20% of our sleep time. This stage is characterized by increased physiological arousal, "alert and awake" brain waves, and vivid dreaming.