THEORIES OF NIGHTMARES IN COGNITIVE NEUROSCIENCE AND PSYCHOLOGY Master Degree Project

.......................................................................................................................................... 2 Introduction ..................................................................................................................................... 4 Theories of Nightmares in Cognitive Neuroscience and Psychology ............................................ 6 Dreams and Nightmares: subjective experiences during sleep ....................................................... 6 Concepts of dreams and nightmares ........................................................................................... 7 Measurements of dreams and nightmares ................................................................................. 11 Phenomenological level of description ..................................................................................... 14 Dream form and dream content ............................................................................................. 15 Sensory input and motor output ............................................................................................ 28 Quantitative level of description ............................................................................................... 28 Prevalence and frequency of nightmares ............................................................................... 28 Relationship between Sleep and Dreaming .................................................................................. 31 Physiological correlates of sleep and dreaming ........................................................................ 31 Neural correlates of dreaming ................................................................................................... 34 Why do we Dream? Dream and Nightmare Theories ................................................................... 38 Random activation theories (RAT) ........................................................................................... 38 Mood regulation theories .......................................................................................................... 42 Nightmares as dysfunctionional dreams ................................................................................ 46 Nightmares as functional dreams .......................................................................................... 52 Evolutionary theories ................................................................................................................ 53 What is a Function? ............................................................................................................... 53 Threat Simulation Theory (TST) ........................................................................................... 53 Discussion ..................................................................................................................................... 60 References ..................................................................................................................................... 73 Running head: THEORIES OF NIGHTMARES IN COGNITIVE NEUROSCIENCE AND PSYCHOLOGY 4 Introduction Dreaming is a natural and physiological phenomenon occurring during sleep (Revonsuo, Tuominen, & Valli, 2015). It is considered the most common type of altered state of consciousness (ASC) containing various subjective experiences such as sensations, perceptions and emotional content similar to waking life (Valli, et al., 2005). Because of the similarities to wakefulness, dreams are considered an important source of providing scientific insights into understanding and describing the nature of consciousness (Revonsuo, 1995; 1998). Thus, unlike waking reality where one is aware of conscious experience, to the dreamer the events occurring in dreams are not recognized as a concoction. It is upon awakening that the sleeper realizes the events experienced previously were not real. Similarly, nightmares are a category of dreams vividly experienced by the dreamer involving threatening scenarios, anxiety and other negative emotions (Hartmann, 1998; Nielsen & Levin, 2007). Within the fields of psychology and cognitive neuroscience many theories and hypothesis have been proposed to clarify what dreams and nightmares are, their nature, function and neural correlates (Nielsen, 2011). However, there is still no convincing explanation for why they are experienced so commonly and if they are useful to the organism or not. Dream researchers keep trying to reach consensus in clarifiying conceptual confusions when describing mental states (Hobson, Pace-Schott, & Stickgold, 2000a). Nevertheless, they still disagree in elaborating useful concepts for this research field. Moreover, when it comes to measuring and quantifying empirical data of dreams as to content, form and frequency of occurrence, there is not yet a clear methodological standard that every researcher in the field follows consistently. The various instruments used seem to yield different results (Kahan & LaBerge, 1996; Robert & Zadra, 2008; Schredl, 1999, 2002; Sikka, Valli, Virta, & Revonsuo, 2014; Zadra & Robert, 2012). Data Running head: THEORIES OF NIGHTMARES IN COGNITIVE NEUROSCIENCE AND PSYCHOLOGY 5 yielded by studies should objectively reflect the subjective experience of the dreamer. Thus, the main problem dream research faces involves theoretical explanations of dreams and nightmares and finding a solution into how future guidelines of dream research should be directed. Theories worth considering as explanations for the nature and function of dreams and nightmares should contain a theoretical background that can be supported by empirical evidence. Researchers should reach a more unified understanding about the methodological standards that everybody should follow, to produce valid and reliable empirical evidence about dreams and nightmares. There are three main goals in this present thesis. The first one is to describe in the light of psychology and modern cognitive neuroscience what dreams and nightmares are and why they are so commonly experienced. The second goal is to review the literature on the theories and empirical findings concerning definitions, occurrence, neural correlates and theoretical explanations of these phenomena. The third and last goal of this thesis is to discuss and evaluate the main current dream theories as to their strengths and weaknesses. This will include considering evidence for their overall explanatory power to account for the existence and nature of dreams and nightmares. Furthermore, their strengths and limitations will be contrasted as a guideline into how future research should be directed to achieve a successful clarification for these phenomena. Running head: THEORIES OF NIGHTMARES IN COGNITIVE NEUROSCIENCE AND PSYCHOLOGY 6 Theories of Nightmares in Cognitive Neuroscience and Psychology This thesis will begin by elucidating the current concepts of dreams and nightmares. Next, these phenomena will be explored according to leading investigations in dream research. Furthermore, the three theories that will be discussed are the main ones in cognitive neuroscience and psychology which offer an explanation for both dreams and nightmares using the same underlying principles. These theories are: 1) random activation theories (RATs), 2) mood regulation theories, and 3) evolutionary perspective theories. The RATs conceive dreaming as an epiphenomenon. Researchers supporting this perspective consider dreams as by-products of underlying sleep mechanisms (Antrobus, 2000; Hobson, 1988; Hobson et al. 2000a; 2000b). The second approach claims dreams fulfill psychological functions by regulating emotional concerns and promoting well-being. In this theory nightmares are seen as a dysfunction of the healing process or mood regulatory mechanisms (Domhoff, 2003; Hartmann, 1995, 1996, 1998; Nielsen & Levin, 2007). The third and last approach that will be explored is evolutionary theories of dreaming. These last propose that dreams and nightmares serve a biological function (McNamara, 2004, 2008; Revonsuo, 2000; Valli & Revonsuo, 2007). In the final part of this thesis, overall strengths and weaknesses of each theory will be compared and contrasted to potentially direct future research. Dreams and Nightmares: subjective experiences during sleep Given the various fields of science involved in dream studies an agreement in describing and defining its main notions has been problematic (Pagel, et al., 2001). Therefore, an approach unifying a definition of the basic nature of dreaming (Revonsuo, Tuominen, & Valli, 2015) should be inclusive rather than exclusive (Pagel, et al., 2001). Pagel et al. (2001) propose that by including different concepts and a categorization system, findings from similar studies can be Running head: THEORIES OF NIGHTMARES IN COGNITIVE NEUROSCIENCE AND PSYCHOLOGY 7 objectively compared and integrated. In such a way, the main goal of explaining the phenomenon with a systematic, normative and statistical approach will be succesfully reached (Valli, 2008). Understanding experiential processes such as dreams and nightmares requires studying its features and elaborating a concept that is clear and descriptive of the phenomenon under investigation (McNamara, 2008). Concepts of dreams and nightmares Metzinger (2003) defines dreams as complex, mutimodal and sequentially organized model of the waking world. He claims dreams satisfy important constraints of conscious experience such as presentationality (the feeling of being in the world), globality (the world dreamer is immersed and experiencing subjectively), and transparency (property of availability of active mental representations). According to Revonsuo et al. (2015) dreams are an ASC (altered state of consciousness) occurring during sleep where the dreamer finds himself embodied and immersed in an experiential reality. The concept of d