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information as other aspects of the effects of brain damage on dreaming are investigated. What we can say unequivocally at this point is that, of course, since dreaming is a brain function, brain damage will affect it. How could it be otherwise? 107 The new neuropsychology of dreaming Chapter 9 Dreaming, learning, and memory The idea that dreaming is involved in the reorganization of memory has been around for at least 30 years, but only within the last five has a strong, clear line of evidence been developed. One of the most important scientists working in this area is my colleague Robert Stickgold, and it is his work that forms the backbone of this chapter. The basic hypothesis, for which evidence was previously consistent and positive but not impressively robust, is that rapid eye movement (REM) sleep subserves consolidation of memory. This hypothesis is appealing because the brain is activated and dreams are composed of memory fragments. This hypothesis has been borne out by recent experiments, although it now appears that non-REM (NREM) sleep is equally important. More interestingly, the dream memory plot has thickened in two important ways: 1. Thanks to progress in cognitive neuroscience, the learning and memory processes that sleep may affect have been better characterized and differentiated. 2. Thanks to progress in basic sleep neuroscience, the brain dynamics that appear to support the differentiated aspects of learning and memory are now known in enough detail to allow modelling of the sleep learning processes. 108 As I have constantly repeated throughout this book, we need, always, to maintain a distinction between dreaming as a conscious experience and REM or late-night NREM sleep, the physiological states of the brain underlying the conscious experience. Just as REM sleep can run without our ever remembering dreams, so we suppose can learning and memory reorganization take place without our ever being aware of it. The best we can hope for is that our new, formalist approach to dreaming might help us to understand the rules of memory reorganization. REM sleep and learning in animals Two complementary theories were adopted in the early days of studying sleep and learning in experimental animals. Rats were used for this work because cats, despite much more being known about their brains, are such poor learners. Cat owners will object to this invidious comparison surely their beloved pets are at least as clever as rats. But cats are domesticated and don t need to learn much to survive. Rats are still wild and need to adapt to much more difficult life conditions. In the first theory, sleep was measured after exposure to new learning, and REM sleep was found to increase as learning increased. In the second theory, REM sleep was prevented; this impaired learning. In both cases, the focus was on REM sleep. In the case of the post-exposure theory, the increase in REM sleep was often surprisingly delayed and time-limited, leading Carlisle Smith to propose the concept of a REM sleep window for the consolidation of learning. This concept is akin to critical periods in development, which also involve learning, and which may also involve REM sleep because that state is so prevalent in immature animals. As far as dreaming is concerned, the data that are most relevant to considerations of the timing of learning and of a REM sleep window 109 Dreaming, learning, and memory in humans are the surprising delays in incorporating new location data reported by travelling dream recorders such as Michel Jouvet and the systematic lab work on the dream incorporation of experiential data by Tore Nielsen. As mentioned earlier, both sources indicate that it may take several days, even a week, for the brain to get around to using new information to change its mind. It is thus clear that, in considering behavioural repertoires, we are confronting long-term processes and we should not expect to find that all post-exposure learning takes place overnight. How can recurrent dreams be explained? Dreaming has remarkably consistent features from individual to individual and from night to night. We call these features formal to indicate the difference from what we call content. By formal, we mean that dreams are visual and intensely emotional, have a peculiar logical quality, and times, places, and people are infinitely plastic and changeable. In other words, dreaming is recurrently bizarre, and it is the recurrence of the bizarre features that we think determines the assumption by most people that the content is repetitive. We know that content itself can be repetitive, especially in the case of traumatic dreams, which we discussed in Chapter 6. But when we ask normal inidviduals to produce records of the recurrent dreams they claim to have, we are impressed by the fact that what is recurrent is the formal features, e.g. anxiety may be a common element to dreams. Well, anxiety about what? Anxiety about exams, for example. That s not a bit surprising if we think that anxiety or emotion play a large part in dream construction. What things are people anxious about? They are anxious about performance and performance evaluation, and what performance evaluation is more stressful or important to people than exam performance? Consequently, we may have exam dreams as one of the recurrent themes. 110 Dreaming Exam dreams are, however, often quite different from one another in orientational detail they take place in different rooms and [ Pobierz całość w formacie PDF ] |