Revision Notes: Sleep
* Nature of sleep, including sleep stages and lifespan changes and lifespan changes in sleep. * Functions of sleep, including evolutionary explanations and restoration theory.
Nature of sleep
* Sleep is a different state of consciousness where responsiveness to the external environment is diminished. * It occurs daily as circadian rhythms and is composed of an Ultradian cycle of separate stages. * With the intention of the electroencephalograph (EEG), psychologists were able to investigate brain activity occurring during sleep and concluded that it was composed of identifiably different sequential stages. (Electrical activity or brain waves). * Electro-oculograms (EOGs) measure eye movement, and Electromyograms (EMGs) measure muscle movement and have been used to distinguish the stages and cycles of sleep. * Sleep is circadian as it happens once a day however it is also Ultradian as the stages are repeated within a cycle. Each cycle is approximately 90 minutes and most people experience 5-6 cycles a night. Stages one to four are slow wave sleep (SWS) and stage five is rapid eye movement sleep (REM). * Brain is active during sleep and this activity can be measured (EEG). Different stages of sleep show different patterns alpha, delta and theta waves. * One cycle takes about 90 minutes; later in the night there is more REM sleep and less SWS.
Stages of sleep
STAGE ONE: Beginning of the sleep cycle. Alpha waves disappear and are replaced by low-voltage slow waves. Heat rate declines and muscles relax. This is a light sleep and the sleeper can easily be woken. Brain produces high amplitude theta waves, which are very slow brain waves – lasts 5-10 minutes.
STAGE TWO: A deeper state, in which the sleep is still easily woken. Short bursts of sleep spindles are noticeable, together with sharp rises and falls in amplitude known as K-complexes. Lasts about 20 mins.
STAGE THREE: Sleep becomes increasingly deep, and the sleep difficult to wake. Sleep spindles decline, being replaced by long, slow delta waves. Heart rate, blood pressure and temperature decline.
STAGE FOUR: Deep sleep, where delta waves increase and metabolic rate are low. The sleeper is difficult to wake. Growth hormones are released and incidences of sleepwalking and night terrors may occur. 30 mins.
The sleeper spends about 30 minutes in stage 4 sleep, with about an hour passing in total from stage 1 to stage 4. Stage 3 is re-entered, then stage 2 and then the sleep enters an active stage of sleep called rapid eye movement (REM) about 90 minutes after failing asleep.
REM: Eye movements are noticeable, heart rate, respiration etc. Increase and dreaming occurs.
Another 15 minutes of REM sleep, the sleeper re-enters 2, 3 and 4 in that order then another cycle begins. It is common to go through about five Ultradian cycles in one night. As the night progresses, the sleeper spends more time in REM sleep and less time in the other stages. This pattern is fairly universal; although there are development differences.
Dement and Kleitman (1957)
* Conducted highly controlled experiments in a sleep lab using biological measurements (e.g. EEG). * 9 male participants for 61 nights.
* Participants were woken at each different stage of sleep and asked a series of questions. * Those awakened during REM sleep (identified by the EEG) reported dreams 79% of the time and only 7% in NREM. * + Was an important piece of research in that it was the first piece, which objectively correlated brain states with dreaming. * - Due to artificial environment, the findings may lack ecological validity because participants in research were not allowed to experience normal sleep, they experienced sleep disturbance. Could cause REM and Stage 4 rebound effect. * - Small sample: Not representative.
+ Objective evidence: EEG, EOG AND EMG...
Please join StudyMode to read the full document