Question

Describe in words each phase of wakefulness and sleep. Be sure to include the brain wave rhythm(s) and characteristic of each phase. You should have seven total phases.

What brain areas control sleep and arousal? Describe at least three.

Most researchers believe that consciousness is distributed across much of the brain; describe their thinking about networks in relation to consciousness.

Answer 1

Stages of Human Sleep

Following the discovery of rapid eye movement (REM) sleep in 1953, researchers learned that there are three basic states of consciousness: wakefulness, REM sleep, and non-rapid eye movement (NREM) sleep.

REM sleep is “an active period of sleep marked by intense brain activity. Brain waves are fast and desynchronized, similar to those in the waking state. Breathing becomes more rapid, irregular, and shallow; eyes move rapidly in various directions and limb muscles become temporarily paralyzed. Heart rate increases and blood pressure rises. This also is the sleep stage in which most dreams occur."

REM sleep is thought to play a role in memory consolidation, the synthesis and organization of cognition, and mood regulation. Depriving someone of just REM sleep (by waking the subject upon when he or she enters into REM, but allowing NREM to occur) results both in the person making increasingly frequent attempts to enter REM sleep and spending increased time in REM sleep.

NREM sleep is characterized by a reduction in physiological activity. As sleep deepens, a person’s brain waves slow down and gain amplitude, both breathing and the heart rate slow down, and the individual’s blood pressure drops.

NREM sleep consists of three stages:

·         N1 (formerly “stage 1”) is a time of drowsiness or transition from being awake to falling asleep. Brain waves and muscle activity begin slowing down in this stage. People in N1 sleep may experience sudden muscle jerks, preceded by a falling sensation.

·         N2 (formerly “stage 2”) is a period of light sleep during which eye movements stop. Brain waves become slower, with occasional bursts of rapid waves (called sleep spindles) and spontaneous periods of muscle tone mixed with periods of muscle relaxation. The heart rate slows and body temperature decreases.

·         N3 (formerly “stages 3 and 4”) is called “slow wave sleep” (SWS) and is characterized by the presence of slow brain waves called “delta waves” interspersed with smaller, faster waves. Blood pressure falls, breathing slows, and temperatures drops even lower, with the body becoming immobile. Sleep is deeper, with no eye movement and decreased muscle activity, although muscles retain their ability to function. It is most difficult to be awakened during SWS, and people may feel groggy or disoriented for several minutes after they wake up from this stage. During SWS, some children experience bedwetting, night terrors, or sleepwalking. SWS seems to be associated with bodily recovery, certain types of learning, and central nervous system changes. The amount of SWS a person gets is directly related to accumulated sleep need — the longer a person has been awake, the more SWS he or she gets when sleep occurs.

Although the role each of these states plays in overall health is uncertain, having the right balance between them is believed to be important for obtaining restful, restorative sleep and for promoting processes such as learning, memory, mood, and ability to concentrate. No one sleep state is more important than the other, just as no one organ in your body is more important than the other. Each is necessary for life, as deprivation of any one of those stages has been shown to reduce health and longevity in laboratory animals.There are distinct and typical electroencephalogram (EEG) and physiologic patterns for alert and relaxed wakefulness, for REM sleep, and for each of the stages of NREM. Although the sleep stages are specifically defined, in reality, they gradually merge from one to another.

In the sleep laboratory, two or three EEG channels are typically recorded, mainly to determine whether a patient is awake and, if not, what sleep stage he or she is in. The EEG captures the four types of brain waves that occur during wakefulness and sleep, which are measured in cycles per second (cps)

·         Beta waves occur during daily wakefulness. They have the highest frequency and the lowest amplitude, compared to other waves. These patterns also show a lot of variability.

·         Alpha waves occur during wakefulness and periods of relaxation (i.e., during meditation). These waves are slower, and have less amplitude and variability than beta waves.

·         Theta waves occur during stages 1 and 2 and are slower in frequency and greater in amplitude than alpha waves. As a person moves from N1 to N2 sleep, theta wave activity continues; every few minutes, sleep spindles(sudden increase in wave frequency) and K-complexes (sudden increase in wave amplitude) occur.

·         Delta waves occur during N3 sleep and are the slowest waves with the highest amplitude. Delta sleep is the deepest sleep.