You spend about half the night in stage N2 sleep. Whisper someone’s name during stage N2 sleep, and a K-complex will appear on the EEG. K-complexes can also be provoked by certain sounds or other external or internal stimuli. The EEG tracings also show a pattern called a K-complex, which scientists think represents a sort of built-in vigilance system that keeps you poised to awaken if necessary.

Scientists believe that when spindles occur, the brain disconnects from outside sensory input and begins the process of memory consolidation (which involves organizing memories for long-term storage). Large, slow waves intermingle with brief bursts of activity called sleep spindles, when brain waves speed up for roughly half a second or longer. Your brain’s electrical activity is irregular. Your eyes are still, and your heart rate and breathing are slower than when awake. This first stage of true sleep lasts 10 to 25 minutes. However, not everyone experiences stage N1 sleep in the same way: if awakened, one person might recall being drowsy, while another might describe having been asleep.

People in stage N1 sleep lose awareness of their surroundings, but they are easily jarred awake. Body temperature begins to drop, muscles relax, and eyes often move slowly from side to side. On the EEG, the predominant brain waves slow to four to seven cycles per second, a pattern called theta waves (see Figure 1). In making the transition from wakefulness into light sleep, you spend about five minutes in stage N1 sleep. The three stages of quiet (non-REM) sleep Stage N1 Unless something disturbs the process, you will proceed smoothly through the three stages of quiet sleep. The transition to quiet sleep is a quick one that might be likened to flipping a switch-that is, you are either awake (switch on) or asleep (switch off), according to research. This is the alpha-wave pattern, characteristic of calm, relaxed wakefulness (see Figure 1). Once your eyes are closed and your brain no longer receives visual input, brain waves settle into a steady and rhythmic pattern of about 10 cycles per second. If you’re fully awake, an EEG records a messy, irregular scribble of activity. When you are awake, billions of brain cells receive and analyze sensory information and coordinate behavior by sending electrical impulses to one another. To an extent, the idea of “dropping” into sleep parallels changes in brain-wave patterns at the onset of non-REM sleep. Sleep specialists have called quiet or non-REM sleep “an idling brain in a movable body.” During this phase, thinking and most bodily functions slow down, but movement can still occur, and a person often shifts position while sinking into deeper stages of sleep. Surprisingly, they are as different from each other as either is from waking. Scientists divide sleep into two major types: The hormone induces drowsiness, and scientists believe its daily light-sensitive cycles help keep the sleep/wake cycle on track.

Levels of melatonin begin climbing after dark and ebb after dawn. As a person reads clocks, follows work and train schedules, and demands that the body remain alert for certain tasks and social events, there is cognitive pressure to stay on schedule.

The circadian rhythm disturbances and sleep problems that affect up to 90% of blind people demonstrate the importance of light to sleep/wake patterns. However, exposure at the wrong time can shift sleep and wakefulness to undesired times. Exposure to light at the right time helps keep the circadian clock on the correct time schedule. In societies where taking a siesta is the norm, people can respond to their bodies’ daily dips in alertness with a one- to two-hour afternoon nap during the workday and a correspondingly shorter sleep at night. Most Americans sleep during the night as dictated by their circadian rhythms, although many who work on weekdays nap in the afternoon on the weekends. When the investigators plotted the times when unplanned naps occurred, they found peaks between 2 a.m. Not surprisingly, many slipped into naps despite their best efforts not to. In one study, researchers instructed a group of people to try to stay awake for 24 hours. (“Circadian” means “about a day.”) This internal clock, which gradually becomes established during the first months of life, controls the daily ups and downs of biological patterns, including body temperature, blood pressure, and the release of hormones.Ĭircadian rhythms make people’s desire for sleep strongest between midnight and dawn, and to a lesser extent in mid-afternoon. For instance, a pacemaker-like mechanism in the brain regulates circadian rhythms. Certain brain structures and chemicals produce the states of sleeping and waking.

Into the waves of the nicht