The Dreaming Mind (Part II)

Recent studies show that even in burns, daydreaming occupies a considerable part of the brain's activity. Why is dreaming so important for brain activity? This section is dedicated to some leading theories, which try to answer the fascinating question of why we dream.

By Etti Ben Simon and Dr. Hagai Sharon, the Tel Aviv Center for Brain Functions and the Faculty of Medicine, Tel Aviv University

of The popular science magazine "Galileo", Issue number 186 March 2014

In part I of the article we saw that the brain is capable of dreaming during most hours of the night. We reviewed the different stages of sleep and the possible dreams in each stage, and saw that dreams also occur outside of REM sleep. Recent studies show that even in burns, daydreaming occupies a considerable part of the brain's activity. Why is dreaming so important for brain activity? This section is dedicated to some leading theories, which try to answer the fascinating question of why we dream.

The question of the importance of the dream has been studied a lot and one can find a large number of theories on the subject. It is important to note that theories about dreaming face a difficult challenge since the dream phenomenon is a complex and contradictory phenomenon: it has individual characteristics (familiar characters or prominent occupations) as well as universal-stereotypes (for example dreams of being chased or flying tend to recur among many subjects and even specific representations such as falling out teeth, embarrassing nudity in public places and more); it involves physical mechanisms (such as a change in body temperature and heart rate) and extensive brains and in general is an island of self-awareness within a general state of unawareness of the environment. If we add to this the fact that we share REM sleep with all mammals it is easy to see that we are facing a difficult challenge. The earlier discovery of REM dreaming led to the fact that a considerable part of the theories put emphasis on this dreaming when it comes to explaining the dream phenomenon as a whole. Furthermore, some theories are based on the activity of a specific mechanism that is active only in the REM stage as part of their explanation of the dreaming activity. We will try to focus on six main scientific theories on dreaming, the claims that support each theory and those that don't, and whether it is a theory that emphasizes the REM stage when it comes to explaining dreaming or allows dreaming in other stages as well.

The psychodynamic theory
This theory is perhaps the oldest and best known scientific theory on the role of dreams. Its developer is the well-known psychiatrist Sigmund Freud, whose path is continued today by the psychologist Mark Solmes from University College London. According to this theory, dreams represent the fulfillment of the dreamer's unconscious desires that are hidden from us by internal censorship mechanisms and therefore are expressed as a strange and illogical plot. The same censorship mechanism also explains the forgetting of the dream, therefore the meaning of the dream will only be revealed by attempts to reconstruct and understand what is behind the plot of the dream. The importance of dreaming, according to this theory, is the representation of repressed impulses and thereby allowing the subconscious to "unload" anxieties, similar to the psychoanalytic principle of overflowing anxieties. This theory therefore places a significant emphasis on the content of the dream and its meaning in the personal aspect, as an unconscious part of the specific self, and therefore fails somewhat in explaining universal dream plots as well as the presumed biological role of REM sleep in non-human mammals (do cows suffer from an Oedipus complex?) . On the other hand, this theory does not at all limit dreaming only to the REM stage (and even began before the discovery of this stage) and emphasizes the content of the dream above and beyond the possible physiological mechanism that produces it. Accordingly, Mark Solmes was among the first scientists to extend the activity of dreaming to additional phases of sleep and showed that activity in various areas that are not essential for the REM phase are necessary for the existence of the dream phenomenon in general (see photo 3 in part A).

Mood regulation theory
This theory, similar to the previous theory, emphasizes the emotional activity that occurs while dreaming. This theory claims that the purpose of dreaming is to improve the emotional state of the dreamer by assimilating new emotional experiences and processing them with emotional experiences from the distant past. This assimilation is done in a way that preserves the self and regulates experiences that may be destructive to the perception of the self. For example, dreams of trauma victims tend to conjure up intense feelings of fear, which are spiced up with some of the details of the trauma. At a certain point, the memory of the trauma is linked to more abstract feelings of fear and helplessness (for example, getting lost in the forest), as well as feelings that are more distant from the dreamer's life. Thus gradually the dreams return to their normal patterns, the memory of the trauma is processed and assimilated into the dreamer's tangle of emotional memories, and the emotional charge of the trauma is reduced. This stage helps to moderate the experiences of the trauma and the negative emotions that accompany it, and therefore helps in the recovery process. A brain mechanism that can support the reduction of the emotional burden of the trauma is related to the lack of activity of certain neurotransmitters during REM sleep, which mediate emotional experience while awake. Therefore, bringing up the traumatic memory without the emotional charge that accompanies it during arousal, can help in the emotional regulation of the trauma memory during REM sleep.

Support for this theory comes from studies in which the subjects' mood before going to bed, their dreams throughout the night and their mood upon waking were examined. The results show that in cases of a negative mood before going to sleep, the dream becomes more positive throughout the night (negative at the beginning of the night and positive towards the morning) and the mood improves upon waking up. Also, studies of sleep deprivation show increased and less regulated emotional activity in subjects who did not sleep compared to those who did - a fact that indicates the importance of sleep for proper emotional regulation. It is also known in the clinical field that in most of the anxiety disorders and depression there is evidence of sleep disorders; In depression, for example, there is much evidence of disturbed REM sleep, which can explain the damage to the regulation of the emotional state. The shortcoming of this theory is related to its focus only on REM dreaming and its inability to offer a general explanation of the importance of dreaming beyond the specific mechanisms of REM dreaming.
Brainstem activation theory
The emphasis in this theory is the evolutionary importance of dream sleep and the current leader is Jerome Siegel from the University of California (UCLA). The brain is more active in REM sleep and waking up from this stage allows a faster return to activity than waking up from deep sleep (due to the sleep inertia phenomenon mentioned in part A). Waking up in an active state can be a great evolutionary advantage and therefore has survived and taken over over the years with the help of the mechanism of natural selection. In the monotherm group, which is a group of mammals that lays eggs and is considered a transitional group between reptiles and mammals (the duck, Platypus, is part of this group), REM sleep mainly activates the brain stem and not higher areas of the cerebral cortex as we see in other mammals. This fact could support that the initial purpose of REM sleep was to constitute some degree of activity within a general state of inactivity.

Additional support for this theory comes from marine mammals (for example dolphins or whales, see image #1). Since these mammals have to emerge from the surface of the water in order to breathe oxygen, they must be in constant motion 24 hours a day. This fact has caused their sleep pattern to be very interesting, they sleep one hemisphere at a time, when the left half of the brain is active and the right half is in deep sleep and vice versa. These mammals have almost no REM sleep, which supports the assumption that REM sleep evolved to allow the brain to be active during sleep; Since these mammals are active around the clock, they had no 'need' to develop REM sleep. Additional support for this theory comes from the timing of REM sleep, which is at its peak while the body and brain temperature are at their lowest (around 4-5 am), a fact that supports the idea that REM sleep 'wakes up' the brain in its least active stages. On the other hand, both REM dreaming and NREM dreaming are phenomena that increase and lengthen towards awakening when the pressure of sleep decreases and the brain becomes more active. Does this fact indicate that the dreams increased in order to wake up the brain or does the brain keep waking up and therefore the phenomenon of dreaming increases? This phenomenon is not enough to explain that recovery is the cause and not the result of brain activity. Another significant disadvantage of this theory is that it does not explain why REM sleep appears only in some animals (mainly mammals and birds), isn't it necessary to protect other animals during sleep as well? However, it is important to note that this theory does not necessarily contradict the other theories mentioned here since additional functions of REM sleep could have been added later in mammalian evolution and essentially 'built' on the presumed initial role of brainstem activation.

AIM theory or the dream as a result of brain activity
Another theory that emphasizes the activity in the brain stem when coming to explain dreaming is the AIM theory developed by the well-known sleep researcher from Harvard University, psychiatrist John Allen Hobson. According to this theory there are three axes that make up the conscious experience. One axis refers to activation (how relatively active the brain is), a second axis to modulation (which neurotransmitters affect brain activity) and a third axis to information (whether the brain receives information mainly from the external or internal environment). According to this model, the REM stage is characterized by the entry of internal information, a relatively active brain and the modulation of certain neurotransmitters only, compared to the waking state where the brain is almost as active as in a dream, but the input of information is both external and internal and the array of neurotransmitters is much richer.

According to this theory, the dream arises from a specific state of brain activity and is seen as an attempt to interpret relatively random activity that comes from the brain stem due to its activation in the REM phase. In fact, it can be said that this theory claims that the dream is a kind of story invented by the 'higher' parts of the cerebral cortex in an attempt to explain random activity that comes from 'lower' areas (the brain stem). Therefore, the phenomenon of the dream as a whole tends to occur because of the special state of the brain at that stage (an active brain with a certain set of neurotransmitters and without the input of external information) and therefore the content of the dream has no special meaning or is personally relevant. In terms of the possible role of a dream in general (without special relation to its content) Hobson hypothesizes that its role is to 'train' the brain in the creation of virtual worlds and patterns of action that the dreamer may encounter in arousal. The training helps activate brain circuits that may be essential for survival so that whether we remember the plot of the dream or not, its activity occurs unconsciously and can still help the dreamer's survival. This answer again brings us closer to thinking about the dream from an evolutionary point of view, as contributing to the survival of the dreaming creature and can explain why fetuses and babies spend most of their time in REM sleep (babies spend about half of their sleep in dream sleep compared to about a quarter when they grow up). A notable disadvantage of this theory is related to its inability to explain dreaming in the NREM stages, a stage in which the brain stem is not activated, and its focus on the specific physiology of REM sleep when it comes to explaining dreaming.

The theory of associative reinforcement

According to this theory, the jumpy plot of the dream and the speed with which the situations change may be more than a source of amusement or wonder about our dreaming mind. According to this model, the increase in associative ability is the main function of dreaming. The content of dreams is rich in memory segments that are no longer related to their initial time or location, in this way the brain manages to actively create new connections that are not possible while awake (for example, playing with a golf ball, thinking how much it reminds me of baldness and suddenly drinking tea with grandfather in the yard...).

This hypothesis could explain the strangeness of the dream plot, and why there is a higher rate of original associations after waking from REM sleep compared to waking from NREM sleep in which the dreams tend to be less strange. The increase in creativity was also reflected in another study in which the ability to perform a mathematical task was tested when it was possible to discover a significant shortcut in performing the task (without the subjects' knowledge). The study clearly showed that twice as many subjects who were allowed to sleep were able to discover the shortcut compared to subjects who were left awake (either during the day or at night), which reinforces the importance of sleep for creating new connections. The disadvantage of this theory is that it does not consider different parameters of the dream as contributing to increasing the associative ability. In most of the studies mentioned above, measures of the dream content were not tested at all. This test could better confirm the importance of REM sleep itself for increasing associativity as opposed to a general change in the level of connectivity between networks that may occur in sleep without a specific relation to dreaming measures. However, it is interesting to note that this theory links the role of dreaming to the presumed role of the phenomenon of daydreaming mentioned above (see also The resting brain revolution), on which many studies have been done recently. These studies also show that people who tend to daydream show a higher creative ability. All of these results support the importance of associations to the learning activity in the brain, which seems to never change. If we combine this idea together with the emotional regulation theory mentioned above, we can assume that dreaming helps in learning new associations, some of which can regulate the mood of the dreamers as well as develop new ways of coping. By activating these situations in a simulated way (without the danger of performing them in reality) it is possible to 'choose' appropriate ways of acting and preserve them over others.

The theory of learning and development
There are several theories that emphasize the importance of dream sleep for learning and development. One emphasizes the possibility that memory formation processes occur mainly during dreaming, while the other emphasizes more general brain wiring processes that are essential for development in general, such as the development of walking, vision, language, etc.

According to the memory consolidation theory, dreaming is essential for the fixation (consolidation) of memories. When we learn new information, it is initially stored in short-term memory (such as remembering a phone number for a few moments or trying to learn more information a few minutes before a test...) which is a relatively sensitive memory with limited capacity. Only after a certain period and if the memory is relevant will it be 'encoded' into a long-term memory that can be used by us almost throughout our lives. It is important to note that the choice of memories that undergo consolidation during sleep gives the impression of a planned process and not of a random process. In many studies on sleep and learning, it was found that emotional memories, or those specifically related to the task being tested in the experiment, were recalled more after sleep compared to neutral or irrelevant memories to the task.

This theory claims that the process of fixing the various memories occurs mainly in the REM stage. Accordingly, many studies show an improvement in the ability to learn new information following a night's sleep (compared to a similar duration but without sleep), when the amount of dream sleep was found to be in accordance with the ability to improve. In addition, functional imaging studies show activation of regions relevant to learning the task during REM sleep. It is important to note that this theory does not limit the improvement to learning only to REM sleep and studies show that different tasks will show improvement following different stages of sleep (for example, improvement in remembering word pairs is consistently observed in accordance with the amount of sleep in stage 3, especially at the beginning of the night). The disadvantage of these studies is the focus mainly on the amount of sleep at each stage usually without dream reports or linking the findings directly to the subjects' dream content. Beyond that, the dream is sometimes presented as a by-product of the processes of forming the various memories that for some reason we are aware of its contents. However, in light of the knowledge that exists today regarding REM and NREM dreaming (as I hope you have already mastered it at this stage) this theory sharpens that it is possible that emotional or perceptual memories will be formed more in the REM stage compared to episodic memories which will be formed mainly in NREM. The link between REM sleep and the formation of emotional memories corresponds with the theory of emotional regulation mentioned earlier, since this formation process can be a major part of the process of regulating emotions and mood that occurs in dreaming.

In a similar way, the theory of development assumes that REM sleep is essential for shaping the connections and connections in the brain activity that is more related to sensory perception and movement. Support for this theory comes from the fact that it is possible to find a correlation between the amount of dream sleep and the immaturity of the brain at birth. The more mammals of a certain species are born with a less developed brain (not yet walking, finding food on their own, etc.), the higher the amount of REM sleep will be. In addition, it is known that a person's dream sleep decreases as he grows older (as mentioned above), a fact that contributed to the thought that dream sleep is especially important for the development of the brain. These two theories can be summarized into a statement that dream sleep contributes to learning, whether it is related to unconscious functions such as walking or vision, or whether to more conscious processes such as memory formation.
In conclusion, it can be said that sleep is not a static state of the brain but rather a complex and organized process in which brain activity changes in a variety of networks. This activity can stabilize memories and emotions, promote different types of learning and even develop creativity. Under this view, it is not difficult to create a mental sequence between dreaming and waking: when awake, brain activity actively changes with the help of the external environment. At night, when we are disconnected from the external environment (off-line state), the brain is freed to internalize everything it has learned and even produce its own content in the form of a dream. Although REM sleep was perceived, from its discovery, as the main stage of dreaming, a continuous and deeper examination of things reveals that as soon as the brain wakes up a little, dreaming begins, regardless of the stage of sleep we are in. The nocturnal scenarios of each and every one of us will probably continue to intrigue us in the coming years while the study of brain functions will progress towards a better understanding of the various dreaming mechanisms mentioned here and their role in health and illness. In a way, dreaming can be thought of as another style of thinking that, although not always under our control, undoubtedly contributes to our development. No wonder then that the dream is a significant part of the brain's activity throughout most of the night's sleep. If we add to this the fact that studies indicate that we daydream even for most of the day, we will come to the conclusion that most of the time our brain is actually living in a dream...
sweet Dreams!

for further reading:
• Andrea Rock: The mind at night - the new science that investigates how and why we dream translated by Yossi Milo. You spent with an employee. 2007
• Yuval Nir et al.\ Dreaming and the brain: from phenomenology to neurophysiology,
Trends in Cognitive Sciences 2009
• Zvi Giora: Psychology of dreams. Broadcasting University Press. 1997
• Els van der Helm and Matthew P. Walker\ Sleep and Affective Brain Regulation.
Social and Personality Psychology Compass 2012
• Siegel JM.\ Clues to the functions of mammalian sleep. Nature. 2005