A Study on Dreaming: Objective Methods to Investigate Dream Content using REM and EEG, Study notes of Neurobiology

Download A Study on Dreaming: Objective Methods to Investigate Dream Content using REM and EEG and more Study notes Neurobiology in PDF only on Docsity! Our eyes move around under the lids while we dream. Why is studying sleep so hard? Sleep and dreaming is a difficult topic to study simply because the participant is asleep so they cannot readily respond or communicate. Furthermore, as dream reports can only be obtained by self-report, they are necessarily subjective. One way to improve the scientific rigour of the study of dreaming is to use physiological measures of the dream state. This possibility was achieved by Aserinsky & Kleitman (1955) just two years before Dement & Kleitman’s study. Research questions:  Can objective methods demonstrate a relationship between dream content and physiological indicators of dreaming?  Does dream recall differ between REM and nREM stages of sleep? (a)  Is there a positive correlation between subjective estimates of dream duration and the length of the REM period before waking? (b)  Are eye movement patterns related to dream content? (c) Procedure:  7 male and 2 female participants, 5 of these studied in detail.  In the day, the participant ate normally (excluding coffee and alcohol) then arrived at the laboratory just before their normal bedtime.  The participant went to sleep with electrodes attached beside the eyes (EOG) and on the scalp (EEG), which fed to the experimenter’s room. Participants were woken (by a doorbell) at various times during the night, asked to describe their dream if they were having one, then returned to sleep.  (a) participants were woken either in REM or nREM (but not told which). They confirmed whether they were having a dream and described the content into a recorder.  (b) participants were awoken after either 5 or 15 minutes in REM sleep. They chose which duration they had been woken up after. Longer REM periods were also allowed. The number of words in the dream narrative was counted (although this was affected by how expressive the participant was).  (c) The direction of eye movements was detected using electrodes around the eyes. Participants were woken after the persistence of a single eye-movement pattern for more than one minute and asked to report their dream. The eye-movement patterns were: mainly vertical, mainly horizontal, both vertical and horizontal, very little or no movement. Findings:  Uninterrupted dream stages lasted 3-50 minutes (mean approx 20 minutes), were typically longer later in the night and showed intermittent bursts of around 2-100 REMs.  the cycle length varied between participants but was consistent within individuals, eg 70 for one, 104 for another.  When woken in nREM participants returned to nREM, but when woken in REM they typically didn’t dream again until the next REM phase (except sometimes in the final REM phase).  (a) Participants frequently described dreams when woken in REM but rarely did from nREM sleep (although there were some individual differences) and this differences was marked at the end of the nREM period (within 8 minutes of cessation of REM – only 6 dreams recalled in 132 awakenings). In nREM awakenings, participants tended to describe feelings but not specific dream content.  (b) Accuracy of estimation of 5 or 15 minutes’ of REM was very high (88% and 78% respectively). REM duration and number of words in the narrative were significantly positively correlated.  (c) Eye movement patterns were related to dream content, eg horizontal movements in a dream about throwing tomatoes, vertical ones in a dream about ladders and few movements in dreams about staring fixedly at something. Conclusion: Dreaming is reported from REM but not nREM sleep, participants can judge the length of their dream duration and REM patterns relate to dream content. DEMENT & KLEITMAN (1957) then and now Dement & Kleitman (1957) is a classic study which explored sleep and dreaming using electronic recording as well as observation and diary methods. It is summarised in the box opposite. Dement & Kleitman’s research aimed to find objective ways to investigate the previously entirely subjective study of dream content by looking for relationships between eye movements in sleep and the dreamer’s recall. Physiological methods in sleep research Although physiological measures of sleep had been available for some years, Aserinsky & Kleitman (1955) were the first to use these to explore the relationship between sleep and dreaming. Two key ideas are important, both using an electroencephalograph (EEG). The EEG is a machine which can detect and record minute changes in voltage associated with electrical activity in nerve and muscle cells when many are active at the same time. This is recorded using macroelectrodes (large, flat electrodes stuck to the skin or scalp). Note that they are recording electrodes – they cannot EEG – break the word down to its parts: Electro (electric) En cephalo (in head) Graph (writing). This will help you to understand and remember the name. used to give the participant an electric shock. An EEG is used to record the simultaneous activity of groups of neurons in the brain. It produces a chart (an encephalogram) which shows how ‘brain waves’ vary, ie how the frequency and amplitude (height) of electrical output from the brain changes over time. The chart provides a record of changes which indicate the sleep stage a person is in (see Figure 2). This shows that we go through several cycles of stages during each night, one of which is dream or rapid eye movement sleep (REM). This is so called because our eyes move rapidly under the lids while we are dreaming but not at other times during sleep. During this stage of sleep; Aserinsky & Kleitman found that when participants were woken they were more likely to report a vivid, visual dream than in other stages (called, collectively, NREM or non-rapid eye movement sleep). In addition, an EEG can be used to record the frequency of eye movements by attaching electrodes to the skin beside each eye. This is called an Electo-occulograph (EOG).