In 1951, an important discovery was made at the University of Chicago. Nathaniel Kleitman's grad student monitored a sleeping boy's brain waves and eye movements and discovered that, every so often, the boy's eyes darted from side to side and his brain activity fluctuated. From these findings, Kleitman concluded that there are five stages of sleep.
Stage 1 sleep is the lightest stage of sleep, lasting anywhere from five to ten minutes. During this stage, the brain relaxes by about 50% and produces theta waves, which occur four to seven cycles per second. If you've ever jolted awake due to a sudden sense of falling or felt very confused after waking up, chances are you were in this stage of sleep.
Stage 2 sleep is where we spend 65% of our sleep time. Although the brain continues to relax, occasional bursts of electrical activity, called sleep spindles, occur twelve to fourteen cycles per second. Also, K complexes appear. During this stage, heart rate and body temperature decrease, muscles relax, and eye movements stop.
Sleep stages 3 and 4 are the deepest stages of sleep. In these stages, delta waves become prevalent and occur one to two cycles per second. In stage 3, these waves happen 20% to 50% of the time, and in stage 4, they happen over 50% of the time. In order for us to have a fulfilling night's sleep, we have to experience these two stages of sleep.
Stage 5 sleep is called rapid eye movement (REM) sleep. Here, we dream vividly and more often than in any other stage. During this stage, the brain kicks into high gear and produces waves that look like those of wakefulness. Heart rate and blood pressure increase, and rapid and irregular breathing occurs. We're in this stage for about 20% to 25% of our night's sleep.
As college students, most of us don't get enough sleep due to homework assignments, studying for tests, and participating in extracurricular activities. We might think that sleep isn't as important as getting good grades in our classes, but we're wrong. It's important that people get enough sleep each night, because sleep reduces stress, improves our memory, and reduces our chances of developing a physical or mental disorder.
Chapter 5 of our Lilienfeld Psychology book