fMRI can only measure blood flow in the brain, it cannot tell us the exact activity of individual neurons and so it can be difficult to tell what kind of brain activity is being represented on the screen. Electroencephalogram (EEG) EEGs measure electrical activity within the brain via electrodes that are fixed to an individual’s scalp using a skull cap. The scan recording represents the brainwave patterns that are generated from the action of millions of neurons, providing an overall account of brain activity. The main 4 of EEG waves are alpha, beta, theta and delta. Scientists can also measure activity through amplitude and frequency. Amplitude is the intensity or size of activity, frequency is the speed or quantity of activity. In the diagram above, the delta wave has the largest amplitude. The beta wave has the highest frequency (14-30 Hz). EEG is often used by clinicians as a diagnostic tool as unusual arrhythmic patterns of activity (i.e. no particular rhythm) may indicate neurological abnormalities such as epilepsy, tumours or disorders of sleep. Strengths Weaknesses EEG has been very valuable at helping diagnose conditions such as epilepsy, depression and schizophrenia because the difference in brain activity can be detected on the screen. It has contributed to our understanding of the stages of It has extremely high temporal resolution (unlike fMRI) it can accurately detect in a single millisecond. Only general information is received from an EEG (the activity of many thousands of neurons). EEG is not useful in pinpointing the exact source of neural activity and does not allow researchers to tell the difference between activity in locations that are very close to one another. potentials (ERPs) ERP’s use similar equipment to EEG (electrodes attached to the however, a stimulus is presented to a participant i.e. picture or sound, and the researcher looks for activity related to the stimulus and investigate how an EEG wave pattern changes in response to the stimulus. This change is an ERP. (Types of brainwaves triggered by particular events).
second, dreams mostly occur in REM and finally, participants did on average go into REM every 90 minutes showing ultradian rhythms. Dement (1960) compared participants who had been deprived of REM sleep with a control group who had been deprived of the same amount of NREM sleep. He found that the REM deprived group were more irritable, more aggressive and unable to concentrate on various tasks. Borbely (1986) found that REM deprived individuals made 31 attempts to re-enter REM on the first night of deprivation (called REM re-bound), 51 attempts on the second night and over 60 attempts on the third… Dement and Borbely’s research suggests that REM is a distinct and significant stage of the ultradian rhythm and also important for our psychological well-being. [Randy Gardner pictured trying to recognise scents] Evaluation to consider… Individual differences A significant problem when studying sleep cycles is the differences observed in people. This makes investigating patterns difficult. Tucker et al (2007) differences in participants in terms of the duration of each stage, particularly stages 3 and 4 (NREM). This suggests there may be innate individual differences in ultradian rhythms which means it’s worth focusing on these differences during investigations into sleep cycles. Lack of ecological validity Sleep cycles are usually investigated with a high degree of control in sleep laboratories. Participants will wear caps with electrodes to monitor EEG patterns and asked to sleep and then be woken up at various points during their cycle. This is both invasive for the participant as well as being very artificial and may lead them to sleep in a way that doesn’t represent their ordinary sleep cycle. This lack of ecological validity could lead to false conclusions. Flexible Randy Gardner’s experience of remaining awake for 264 hours and subsequently recovering 70% of stage 4 and 50% of his REM sleep and little of the other stages. This suggests the degree of flexibility in terms of the different stages may not be as ‘fixed’ as psychologists believed. However, we should consider that Gardner’s results could be unique to him, for example an older individual may have very different results in the sleep they recovered. This means generalisation of such specific cases could be difficult.