AQA Psychology for A Level Year 2 - Student Bk

infradian and ultradian rhythms Infradian – more that 24 hours; ultradian – less than 24 hours. Infradian rhythms The menstrual cycle Oestrogen regulates ovulation, progesterone readies body for pregnancy (endogenous factors). Research study Stern and McClintock: Evidence that menstrual cycles may synchronise through pheromones (exogenous factors). Seasonal affective disorder Form of depression triggered in the winter months and regulated by melatonin, a circannual rhythm. Other research Studies by Aschoff and Wever (bunker) and Folkard et al. (cave) showed longer and shorter rhythms Ultradian rhythms: Stages of sleep 5 stages that occur in a 90-minute cycle: Stages 1 and 2: Alpha and theta waves. Stages 3 and 4: Deep sleep, delta waves. Stage 5: REM sleep. evaluation Evolutionary basis of the menstrual cycle Synchronisation may have an adaptive function because newborns cared for collectively. However, this would also produce competition for the fittest males. Methodological issues in synchronisation studies Many confounding factors not controlled, e.g. stress, diet. Small samples. Evidence supports the idea of distinct stages in sleep Deement and Kleitman (1957) using EEGs showed how REM (dream) sleep is an important part of the sleep cycle. Animal studies Role of pheromones in human behaviour is unclear. Practical application Phototherapy for SAD, effective in 60% (Eastman et al. ). endogenous pacemakers and exogenous zeitgebers Rhythms are affected by body clocks and external cues exogenous zeitgebers and the sleep-wake cycle Exogenous zeitgebers Entrain free-running rhythms. Light Campbell and Murphy – shone light pad on back of knees. Social cues Babies’ rhythms are entrained by bedtimes and mealtimes. endogenous pacemakers and the sleep-wake cycle The SCN Receives info about light directly. Animal studies and the SCN DeCoursey et al. : Sleep–wake cycle disappeared when SCN destroyed. Ralph et al. : Mutant hamsters with 20-hour sleep cycle. The pineal gland and melatonin The SCN passes info to the pineal gland that controls melatonin. evaluation Beyond the master clock Peripheral oscillators are found in many areas of the body. Damiola et al. showed how these can act independently of the SCN. Ethics in animal studies DeCoursey et al. study harmed animals, is this ethically justifiable? Influence of zeitgebers may be overstated Zeitgebers may have little bearing on our internal rhythm, e.g. blind man (Miles et al. ). Methodological issues in studies Light pad study findings not replicated and isolating one zeitgeber may be unrealistic. Interactionist system Attempts to separate pacemakers and zeitgebers may not reflect real-life. Ways of investigating the brain Measuring brain activity and structure. Scanning and other techniques fMRI Detects changes in blood flow to show active areas. EEG Measures brainwave patterns via electrodes. ERP Types of brainwave triggered by particular events that can be extracted from EEG recordings. Post-mortems Deficits during life correlated with brain damage after death. evaluation fMRI + Risk-free and high spatial resolution. – Poor temporal resolution. EEG + Good for diagnosing illness, and high temporal resolution. – Overly general. ERP + Precise measurement of cognitive functions. – Lack of standardised method. Post-mortem + Early pioneering research. – Causation an issue, consent is difficult. circadian rhythms A bodily rhythm that takes about 24 hours to complete. Biological rhythms Biological rhythms Controlled by internal body clocks (endogenous pacemakers) and external cues (exogenous zeitgebers). The sleep/wake cycle Determines sleepiness, but does free-running cycle continue in the absence of daylight? Siffre’s cave study His free-running rhythm extended slightly to 25 hours when deprived of daylight. Other research Studies by Aschoff and Wever (bunker) and Folkard et al. (cave) showed longer and shorter rhythms Core body temperature Associated with improved variations in cognitive performance. evaluation Practical application to shift work Mistakes made when rhythms desynchronised (Boivin et al. ) and poor health (Knutsson). Thus economic implications of research. Practical application Pharmacokinetics applies understanding of circadian rhythms to improve drug effectiveness (Baraldo). Use of case studies and small samples Lack generalisability, e.g. Siffre was over 60 and small samples. Poor control in studies Dim artificial light may have reset the body clock (Czeisler et al. ). Individual differences Sleep cycles vary between 13 and 65 hours in some cases (Czeisler et al. ) and larks/owls (Duffy et al. ). Biological rhythms: revision summaries 55 •