After the discussion you can show the PowerPoint presentation This is to give an overview of the stages of sleep and theories of sleep. There are no illustrations on these slides to enable the teacher to choose the most appropriate illustration form, for example Google images. It is recommended that a handout showing three slides per page is printed off for each student which will allow for note taking. It is then suggested that you show the students the DVD after this presentation, stopping the DVD to remind them of the points made and to enable them to add any further notes that the DVD covers. Activity three is on Sleep Disorders and Treatment, it is recommended that you introduce these before they are mentioned on the DVD.
Sleep Sleep is not the total loss of consciousness, but an altered state where we descend into a state of reduced consciousness. Our body is governed by our body clock or circadian rhythm. One of the most well researched of these rhythms is the ultradian rhythm that governs our sleep/wake cycle.
The stages of sleep The sleeper enters each cycle (which lasts approximately 90 minutes) and there are about 5 cycles per night. Stage 1 lasts for approximately 15 minutes. The Stage 1 lasts for approximately 15 minutes. The body relaxes, heart rate and temperature falls and there s a feeling of drowsiness. The EEG reveals alpha waves and some people experience brief hallucinations especially of falling (a hypnagogic state). This is the lightest stage of sleep and it is possible to awake easily.
Stage 2 This lasts about 20 minutes and the EEG records theta waves which are larger and slower from those in Stage 1. There are however spindles of activity which shows that the sleeping person is responding to external stimuli, such as noise. Like stage 1 sleep, the person is able to be easily woken.
Stage 3 Lasts approximately 15 minutes and now the EEG is showing long, slow delta waves and again some sleep spindles. In this stage it is more difficult to arouse the sleeper.
Stage 4 Lasts approximately 30 minutes and is known as slow wave sleep (SWS) because the EEG shows the brain is still producing delta waves but these are more pronounced than in Stage 3. This is very deep sleep and it is extremely difficult to rouse someone from this stage. There are physiological changes where body temperature, heart rate and blood pressure fall and growth hormones are secreted. It is at this stage that sleep-walking, sleep-talking and night terrors can occur.
Stage 5 This stage lasts approximately 10 minutes in the first cycle and builds up to about an hour in the 4 th and 5 th cycle. The EEG now shows beta waves which are similar to the brain waves of someone who is relaxed but awake. However, it is extremely difficult to wake a person up in this stage. That is why this stage is sometimes called paradoxical sleep. It is this stage that is linked to dreaming (although we do dream in other stages). Here rapid eye movements are in evidence which indicate that the person is dreaming. That is why this stage of sleep is sometimes referred to as REM sleep. The sleeping person in this stage is actually paralysed because the neurotransmitter acetylcholine is blocked which prevents movement. This is good as it is possible that the person may act out their dreams.
The 90 minute sleep cycle We enter stage 1, then stage 2, 3, 4 then back to 3 and 2. We then enter stage 5 (the REM stage). Although we enter the REM stage in each cycle we only spend about 10 minutes in REM sleep during the first cycle. As we progress through the night though, we stay in the REM stage for longer. Therefore both non-rem and REM sleep must be very important and is shown in the majority of mammals including humans.
Sleep Why do we spend about a third of our lives asleep?
Theories of sleep There are several theories of sleep however the most popular are: Restoration theory Evolutionary theory Neurobiological theory Activationsynthesis theory Psychological theory Wish fulfilment theory
Restoration theory (Oswald, 1980) All animals sleep. Therefore it must serve some vital and universal function. According to this theory, the purpose of sleep is to repair and recharge the brain and body thus restoring energy. Oswald claimed that non-rem sleep restores the body and REM sleep restores the brain. We often sleep more through times of illness and stress which lends support to this theory.
Evidence for restoration theory Growth hormone, which is necessary for protein synthesis (needed for tissue growth and repair) is released during stage 4 sleep. High brain activity recorded in REM sleep provides evidence for brain recovery. This also enables brain processes to be renewed and neurochemicals to be replenished. People who completed a ultra marathon (57 miles) slept longer for two nights following the marathon which suggests the body was being restored to its former state.
Evidence against restoration theory Protein synthesis that is needed for tissue restoration is facilitated by the production of amino acids which are only available for 4 hours after eating. Therefore there is a limited time for protein synthesis to occur unless you go to sleep immediately after eating. If restoration is the full explanation of sleep we would expect that those deprived of sleep would sleep for the time they missed whereas in fact they only sleep for about 25% extra. Neurochemicals rise and fall during all stages of sleep so it is doubtful that they are being replenished during REM sleep.
Evolutionary theory (Meddis, 1975) Sleep deprivation studies have shown that sleep is vital as death will occur if sleep is not possible. Therefore sleep is necessary for survival. Some animals sleep in the day, others at night. Others sleep for longer. These differences in patterns suggest that sleep patterns have adapted to maximise survival. For example predators such as lions, tigers etc sleep for longer than prey such as cattle. Mice and other similar animals have a high metabolic rate and thus conserve energy by sleeping for long periods, unlike cows who have a low metabolic rate. They don t have to conserve energy and therefore only sleep for about 3 hours.
Research against evolutionary theory It can be argued that prey should sleep longer than predators as sleep provides protection from predators. Sleep does not provide sufficient energy conservation as proposed in the mouse/cow example. In fact sleep would only provide the equivalent of one slice of bread and therefore is not a sufficient explanation of energy conservation.
Neurobiological theories: 1. The activationsynthesis theory by Hobson and McCarley, 1977 During the REM stage of sleep the brain is very active. The body though is paralysed so our senses do not send information to the brain information such as sight, sound, touch, taste and smell. However, because the brain is very active during this stage of sleep the brain interprets this information as if it is coming from our senses. The brain tries to make sense of this activity by producing dreams. Therefore the brain is activated in a random way and this information is synthesised (put together) into a story. That story is a dream.
Evidence to support activationsynthesis theory If an area of the brain is stimulated that controls balance the dreamer is likely to report they have had a dream about falling, therefore activation of certain areas of the brain will produce a dream
Evidence against the theory There is more meaning to our dreams than activationsynthesis theory predicts. For example, people recognise parts of their dreams from what has happened to them the day before for example. This means that dreams are not just the by-product of random brain activity. Sometimes we have lucid dreams, where we are aware we are dreaming. It is also possible, given certain equipment to be able to signal when we are having lucid dreams. This again means that dreams are not just random brain activity and that to a certain extent they are under our control.
Neurobiological theories: 2. Reverse-learning Theory (Crick and Mitchison, 1983) This theory states that the key function of dreaming during REM sleep is to un-learn the information that is no longer important or that is no longer needed. This frees up space in the cortex and so ensures there is room for new and important information. This theory states that the neurological pathways that help our memories to be consolidated are made more efficient through REM sleep. In short it states that we dream to forget
Evidence to support this theory Dolphins are mammals but unlike other mammals they do not enter REM sleep. It has been proposed that it is because their brain is larger (relatively) than the human brain and therefore does not need to get rid of unwanted information.
Evidence against this theory This theory cannot explain how we know what information to get rid of and what might be important in the future.
Psychological theory: Sigmund Freud (1900) This is perhaps one of the most famous theories in psychology and tries to explain that people dream as part of their unconscious needs. This theory proposed that dreams are the royal road to the unconscious mind. We dream, says Freud, in symbols as a great deal of what we dream is about wish fulfilment and what we wish for can be so shocking that our psychological defences change the images into something that is more socially acceptable. Freud distinguishes between two types of dream content: the manifest content story of the dream, and the latent content the meaning of the dream. So for example if a dreamer reports falling in a dream this might represent an unconscious belief that they are not in control of their lives or could depict a fall from grace.
Evidence to support Freud s theory of dreams There is in fact little scientific evidence to support this theory. Rather Freud relied very much on case studies which he analysed himself. By their nature case studies lack generalisability and there are problems with validity when the person proposing the theory is responsible for analysing the manifest content of a dream. There is a possibility that the analysis may fit the theory.