AQA Psychology for A Level Year 2 - Student Bk

The specification says… Biological rhythms: Infradian and ultradian rhythms Biological rhythms: infradian and ultradian rhythms. Infradian rhythms are those that take longer than 24 hours to complete. Here, we discuss two examples of these – the menstrual cycle and seasonal affective disorder (SAD). Also featured on this spread are the stages of sleep (more commonly referred to as the sleep cycle ). The sleep cycle is an example of an ultradian rhythm: biological rhythms that take less than 24 hours to complete and may often occur more than once over the course of a day. Key terms Infradian rhythm – A type of biological rhythm with a frequency of less than one cycle in 24 hours, such as menstruation and seasonal affective disorder. Ultradian rhythm – A type of biological rhythm with a frequency of more that one cycle in 24 hours, such as the stages of sleep. Concepts: EEGs and sleep It is the case that not all dreams occur during REM sleep. Hypnogogic dreams occur during stages 1 and 2, shortly after drifting off to sleep, and are those in which we may experience the feeling of being out of control or that we are falling. These dreams are significant for the fact that we often wake with a jolt (a hypnic twitch ) when we are sure we are about to hit the ground! Question Brainwave activity during sleep is measured in sleep labs using an EEG. What are the strengths and limitations of EEGs in the context of this research? @ookx hs @ookx hs Infradian rhythms The menstrual cycle The female menstrual cycle, an example of an infradian rhythm , is governed by monthly changes in hormone levels which regulate ovulation. The cycle refers to the time between the first day of a woman’s period, when the womb lining is shed, to the day before her next period. The typical cycle takes approximately 28 days to complete (though anywhere between 24 and 35 days is generally considered normal). During each cycle, rising levels of the hormone oestrogen cause the ovary to develop an egg and release it (ovulation). After ovulation, the hormone progesterone helps the womb lining to grow thicker, readying the body for pregnancy. If pregnancy does not occur, the egg is absorbed into the body, the womb lining comes away and leaves the body (the menstrual flow). Research study Although the menstrual cycle is an endogenous system, evidence suggests that it may be influenced by exogenous factors, such as the cycles of other women. A study by Kathleen Stern and Martha McClintock (1998) demonstrated how menstrual cycles may synchronise as a result of the influence of female pheromones. McClintock involved 29 women with a history of irregular periods. Samples of pheromones were gathered from 9 of the women at different stages of their menstrual cycles, via a cotton pad placed in their armpit. The pads were worn for at least 8 hours to ensure that pheromones were picked up. The pads were treated with alcohol and frozen, to be rubbed on the upper lip of the other participants. On day one, pads from the start of the menstrual cycle were applied to all 20 women, on day two they were all given a pad from the second day of the cycle, and so on. McClintock found that 68% of women experienced changes to their cycle which brought them closer to the cycle of their ‘odour donor’. Seasonal affective disorder (SAD) SAD is a depressive disorder which has a seasonal pattern of onset, and is described and diagnosed as a mental disorder in DSM-5 . As with other forms of depression , the main symptoms of SAD are persistent low mood alongside a general lack of activity and interest in life. SAD is often referred to as the winter blues as the symptoms are triggered during the winter months when the number of daylight hours becomes shorter. SAD is a particular type of infradian rhythm called a circannual rhythm as it is subject to a yearly cycle. However, it can also be classed as a circadian rhythm as the experience of SAD may be due to the disruption of the sleep/wake cycle and this can be attributed to prolonged periods of daily darkness during winter. Psychologists have hypothesised that the hormone melatonin is implicated in the cause of SAD. During the night, the pineal gland (see next spread) secretes melatonin until dawn when there is an increase in light. During winter, the lack of light in the morning means this secretion process continues for longer. This is thought to have a knock-on effect on the production of serotonin in the brain – a chemical that has been linked to the onset of depressive symptoms. Ultradian rhythms One of the most intensively researched ultradian rhythms is the stages of sleep – the sleep cycle. Psychologists have identified five distinct stages of sleep that altogether span approximately 90-minutes – a cycle that continues throughout the course of the night. Each of these stages is characterised by a different level of brainwave activity which can be monitored using an EEG (see page 44). Stages 1 and 2 of the ‘sleep escalator’, as it is sometimes known, are light sleep where the person may be easily woken. At the beginning of sleep, brainwave patterns start to become slower and more rhythmic ( alpha waves ), becoming even slower as sleep becomes deeper ( theta waves ). Stages 3 and 4 involve delta waves which are slower still and have a greater amplitude than earlier wave patterns. This is deep sleep or slow wave sleep and it is difficult to rouse someone at this point. In stage 5, REM sleep, the body is paralysed yet brain activity speeds up significantly in a manner that resembles the awake brain. REM stands for rapid eye movement to denote the fast, jerky activity of the eyes under the eyelids at this point. Research has suggested that REM activity during sleep is highly correlated with the experience of dreaming. Sleep stages Stage 1 Theta waves Stage 2 Light sleep Stages 3 & 4 Delta waves REM sleep The different patterns of brainwave activity during sleep. Chapter 2 Biopsychology 48 •