The Dreaming Mind (Part I)

It is commonly thought that dreams only occur during a stage of sleep characterized by rapid eye movements (a stage known as REM sleep), but new findings show that the brain does not stop thinking even during deep sleep

By Etti Ben Simon and Dr. Hagi Sharon, Center for Brain Functions Tel Aviv. The article was first published in the Galileo journal

of The popular science magazine "Galileo", Issue number 185 February 2014

It is commonly thought that dreams only occur during a stage of sleep characterized by rapid eye movements (a stage known as REM sleep), but new findings show that the brain does not stop thinking even during deep sleep (Non-REM stages), especially in the later parts of sleep. In this article we will review these states of dreaming and the differences between them, we will wonder what is the supposed importance of dreaming in general, and whether it may have a connection to the thinking that occurs while awake. sweet Dreams!

"I gave up trying to find out how and where REM dreams begin, because I couldn't find a point where dreaming stops" dream researcher David Fox from the book "The Mind at Night".

Dreams have fascinated the human race since the dawn of mankind. This is not a surprising fact considering the strange situation in which dreaming occurs. A loss of consciousness to the point of almost complete sensory disconnection from the external environment, a nightly script revealed only to us, but nevertheless its end is not known in advance and the scenes in it change too quickly for us to understand. While in waking life we ​​are used to receiving information from the environment and planning our actions, in a dream we are "parachuted" into a 'reality' that in most cases is not under our control, strange, unfamiliar and sometimes has different rules than the reality of the waking world. This situation probably led to the perception of the dream as a message from the gods, a perception that prevailed for thousands of years until the proposal of more scientific explanations for the dream phenomenon during the 19th century.

The finding that contributed the most to the scientific examination of the dream phenomenon was undoubtedly the discovery of the stage of sleep characterized by rapid eye movements (REM, see diagram no. 1) in 1953. Eugene Asrinsky, under the guidance of the sleep researcher Nathaniel Kleitman from the University of Chicago, first followed Eye movements of subjects for an entire night, when his son is often used as a guinea pig and after a large number of subjects, Kleitman's daughter was also added to the array. Today it is amazing to think that the existence of this sleep stage was not described before. After all, anyone who has ever seen another person sleeping can notice the rapid eye movements that accompany the REM stage, especially in babies and children. Therefore, in principle, the relationship of this phase to dream sleep could have been characterized by the people of antiquity to the same extent as it was characterized in the fifties of the last century. It is possible that the prevailing attitude for hundreds of years, initially the popular one that saw dreams as a matter of the "mind" and not of the body and later of science that saw sleep as "total rest" of the brain which is not a complex process but a static state, prevented people and scientists alike from characterizing a phenomenon that is right under their noses. In any case, Asrinsky and Kleitman's discovery that rapid eye movements represent dream sleep provided, for the first time in the history of sleep research, an objective and externally measurable marker that makes it possible to know whether the subject is dreaming instead of being satisfied only with arousal of the subjects and subjective reporting. Countless studies since then have proven that waking up subjects in the REM phase will lead to reporting a dream in more than 80% of cases. These findings led to the common perception that REM sleep is equivalent to dreaming and that dreaming is not possible in other sleep stages. Accordingly, subjects who were asked whether they dreamed when they were awakened from non-REM sleep stages (Non-REM, NREM) reported dreams only in 8% of cases.
A turning point in the example that dreaming occurs only during REM sleep came only in the 70s, when researchers changed the question they asked subjects immediately after waking them from their sleep. Instead of asking did you have a dream? The investigators asked: Did a thought cross your mind before I woke you up? Surprisingly, changing the wording of the question led to a jump in reports of dreaming in NREM stages to more than 50% of the cases. Why was it necessary to change the question in order to reach these findings? To try to answer this question we will turn to focus on the features that distinguish between dreaming during REM and during NREM and perhaps we will be able to expand what we tend to define as a dream.

Characteristics of REM and NREM dreaming

A dream can be defined in general as a conscious experience during disconnection from the external environment (during sleep) accompanied by sensory hallucinations that have a sense of a realistic occurrence, and usually tends to develop as a plot. Typical experiments in the field of dream research accompany the subject's night's sleep in combination with some kind of electrophysiological imaging (for example, EEG, see picture no. 1) and in accordance with the research question, the subjects are awakened in different stages of sleep and collect detailed reports on the plot of the dream. In order to try to quantify the dream experience in a way that allows comparison between subjects, there are agreed upon questionnaires that test several axes in the plot of the dream. For example, the dreamer's level of involvement in the plot and his/her control over the events that took place, the type of emotions experienced, the number of people in the dream and even having an unethical activity in the dream. These reports undergo a verbal, numerical and content analysis and are compared across a large number of subjects or sometimes over years in the same subjects.
From these studies it appears that the plot of the dream is not always as strange or unexpected as people tend to think and in many cases reflects the character traits or prominent occupations of the dreaming person. About 70% of the dreams tend to include a familiar figure, occur in everyday places (mainly inside a house or room and less in the workplace) and most of them will deal with issues related to family, friends and familiar activities. And as the American dream researcher, Calvin Hall, put it, "Children dream about their parents while their parents dream about them, and husbands dream about their wives while they dream about them." Only in the minority of cases (about 20%) will the dream not include familiar people or include unusual activities. Famous or public figures appear in less than 1% of dreams, a fact that corresponds with the consistent finding that current events hardly ever enter the dream. On the other hand, it can be said almost universally that the dream is mainly intended for the dreamer since in 95% of the reports the main character in the dream is the dreamers themselves. This fact corresponds with new research literature on the phenomenon of daydreaming (cf The resting brain revolution), in which it was also discovered that in most cases the subjects tend to reflect mainly on themselves and their misdeeds. Even the timeline, which sometimes seems to be disrupted in a dream, remains faithful to the source and dreams that were experienced as particularly long plots were indeed found in studies to occur in long dreaming stages. So what is so different about dreams after all?

Since over the years more studies have been done on REM dreaming, there is more detailed information on the prominent features of dreaming at this stage and the brain activity that accompanies it, so we will start with it.

Characteristics of REM dreaming

sensory hallucinations
The plot of the dream is almost always accompanied by sights, sounds and movement. Smell and taste are found in less than 1% of all dreams (a reasonable fact considering that it is quite difficult to imagine a smell..). It is interesting to note that people who became blind before the age of 5-6 do not see mirrors in their dreams and accordingly report more sensations of touch, smell and taste during the dream. Blindness after the age of 6 allows imagining images in a dream, which implies a critical period for the development of the visual system in the brain, including the high capacity for abstraction and imagination needed in a dream. By the way, when REM sleep was first discovered, the thought arose that the eye movements reflect watching a "movie" which is the dream, I thought it must be admitted that it is quite intuitive, but studies on blind people from birth who also demonstrate rapid eye movements during the REM phase refuted this claim.
The extensive sensory dynamics during dream time is supported by brain studies, which show significant activity in areas of vision, hearing, and movement planning during REM sleep (see image #2). The very realistic feeling of the dream is actually due to the fact that during the dream we use the same areas with which we 'see' and feel the world also while awake. For example, seeing a house in a dream will activate most of the mechanisms that will also be activated when we see a house in a dream. In addition to areas of primary sensory perception and processing, also an area of ​​sensory integration located at the junction between the posterior (occipital), parietal (parietal) and lateral (temporal) lobes (the TPJ area) has been shown to be especially essential for dreaming (of any type) and damage to it leads to the complete absence of dreaming despite Normal REM sleep (see picture 3).

A reduction in the capacity for conscious choice or self-reflection

The plot of the dream usually tends to develop by itself and our ability to navigate it is extremely marginal (an exception to this point is the fascinating case of a lucid dream in which experienced subjects manage to be aware that they are dreaming and thus control to some extent during the dream, see more details in Appendix A) . A good way to check if we are in a dream is to try asking ourselves "How did I get here?" While this comment is an easy question to answer during a dream you will be surprised to discover how little information you have about plot twists. The ability to cast doubt is also greatly reduced during a dream and scenarios that we would cast doubt on while awake (for example talking to people who have passed away) arouse little, if any, bewilderment during the dream. The reality of the dream is experienced as the real reality and the dreamers do not doubt the plot, however strange it may be. In terms of brain activity, this phenomenon can be explained by a decrease in the activity of the planning and control networks during REM (see picture 2) which are responsible, among other things, for a logical examination of events and self-reflection.

An increase in emotional expression
Most of the dreams in the REM phase are accompanied by a prominent emotional experience, often more extreme in terms of the intensity and manifestations of emotion than when awake, especially in the longer dreams that occur before waking up. Studies show that over two thirds of the emotions that appear in a dream are usually from the negative spectrum (such as fear, anxiety or anger) and only about 20% are accompanied by a positive emotion. It is interesting to note that sexual activity only appears in about 10% of dreams and is not as common as people tend to think. In terms of brain activity, functional imaging studies show extensive activity in the areas involved in emotional processing during REM dreaming (see picture 2), where in some areas the activity is even higher than during wakefulness.
Forget the dream
A striking feature of most REM dreams is that we forget them. With the exception of cases where we woke up during the dream (whether because of the plot or because of a curious scientist) chances are we won't remember anything about the plot of the dream. It is important to note that we all dream, whether we remember the dream or not, and this fact has been proven hundreds of times in laboratory studies. It was also found that people who tend to remember dreams are those who are more inclined to daydream during wakefulness. You can try to improve the forgetting of the dream by keeping a dream diary. When waking up, before any other action, it is possible to write down or record what we remember from the dream. This action tends to help over time in the ability to remember details of the plot of the dream, but when the recording is stopped, the forgetting of the dream returns very quickly.

Over the years several theories have tried to explain why the brain goes to the trouble of creating complex plots only to abandon them upon waking. There is no definitive answer to this yet, but we can assume that since the array of neurotransmitters (neural messengers) in the brain is very different during REM sleep compared to wakefulness, we are unable to create memories during this sleep phase. Also, our inability to determine the plot of the dream to some external marker in the environment also makes it difficult for us to produce a memory of the plot of the dream. Whatever the reason, most of our night dreams remain hidden, which makes them even more mysterious to us.

Characteristics of NREM dreaming

Studies on NREM dreaming reveal similarities to REM dreaming but at the same time also unique features of dreaming in these stages. NREM sleep contains several stages in which a wider variety of dreams can be found. NREM sleep can be roughly divided into light sleep (stages 1 and 2) and deep sleep (stage 3) (see diagram 1). Thoughts or dreams can be found in all these stages although the chance is greater as the sleep continues and approaches waking.
At the beginning of sleep, in stage number 1, there is a phenomenon known as "hypnagogic images". This phenomenon is characterized by short mental images that are usually affected by the day's activity and now it is over, ZA is affected by episodic memories (event memory - the ability to remember and catalog events that happened to a person explicitly, that is verbal and visible and not hidden or subconscious). For example, if subjects played a certain video game for several hours that day, for example the game Tetris, they would report images of falling stones during falling asleep. Despite the clear connection to today's activities, these sections are a representation and are not an exact copy of the events as we remember them. For example, in the Tetris study, the subjects never reported that they sat in the laboratory and watched themselves play Tetris or that the falling stones appeared on a computer monitor. The fact that dreaming does not accurately reflect the past day's events (if at all) is consistent and common to all types of dreaming known to us.

However, dreaming in stage 1 is the closest to the events of the previous day, of all the different stages of dreaming and is a stable phenomenon reported by over 60% of the subjects. This dreaming tends to be more static, distinctly shorter than REM dreams and less narrative. Despite this, even at this stage you can find reports of dreams with a short plot that include the dreamer or other familiar characters. These dreams will not usually include emotional experiences, will be more similar to normal reality and will mainly include visual segments. It is interesting to note that selective deprivation of REM sleep (i.e. waking up the subjects every time they enter REM sleep without interrupting the other sleep stages) causes the phenomenon of hypnogogic images to become more frequent and create brief visual hallucinations even while awake. This fact suggests a possible connection between this phenomenon and REM dreaming. Similarly, this stage also includes a change in eye movements, but unlike the rapid eye movements that accompany the REM stage in stage number 1, the eye movements are slow and circular and in many cases this physiological sign heralds the onset of sleep.

Even later in sleep, in stage number 2, the dreams tend to be less strange and more familiar compared to the dreams that occur in the REM stage. They have less social interactions and, like dreams from the previous stage, they are also less likely to involve characters who are not the dreamer. At the end of stage 2, the sleep deepens and stage 3 begins, known as the deep sleep stage. This phase varies in length throughout the night similar to the REM phase. But while REM stages are short at the beginning of the night and longer towards awakening, deep sleep is longer at the beginning of the night and shorter towards the morning.
At the beginning of the night, when the stage of deep sleep is the longest, the chance of dreaming is relatively low and as the night goes on the chance of dreams increases. It is important to note that awakening from deep sleep is usually accompanied by a temporary impairment of general functions (perception, movement, etc.), a phenomenon known as sleep inertia (see Appendix B). This fact may affect the subjects' ability to remember or report their dreams. Despite this, about 60% of the awakenings in the deep sleep phase are accompanied by a report of dreams. These reports are similar in many characteristics to REM dreaming (for example in the scene of the event or in the involvement of the self) but they are usually shorter and less complex than REM dreams. Also, similar to stage 2, these dreams tend to involve less feelings or characters that are not the dreamer (for example, a crowd or unfamiliar characters that are relatively common in REM dreaming).
Studies on NREM dreaming have added and discovered that in the field of emotions arising in dreams, there is a slight tendency towards positive emotions in NREM dreams and an opposite tendency, towards negative emotions, in REM dreams (as mentioned above). Also, the level of social interaction is higher in REM dreams (which tend to contain more unfamiliar characters) compared to NREM dreams. Also on the question of what is the main source of memory in the variety of dreams, researchers found that it is mainly episodic (that is taken from the day-to-day experiences of the dreamer) in NREM dreams, while REM dreams rely more on a general memory that is not directly related to the experiences of the previous day.
In general, it can be said that NREM dreaming is more reminiscent of thought processes compared to REM dreaming. It has less distortion of reality, fewer hallucinations, a more abstract perception of things and not necessarily sensory, and a timeline that is more disjointed and less continuous (the plot axis is less noticeable). It can be assumed that this type of dreaming will activate similar mechanisms to daydreaming, which is common during the day, and will actually create a continuum between the common styles of thought while awake and during sleep. These differences are mainly qualitative and can indicate the type of brain activity that occurs in the different types of dreaming. It is known, for example, that during REM there is a broad global activation of many centers in the brain that can support more complex and developed 'plots', while in other stages of sleep the functional activation is more focused and does not 'recruit' additional networks.
However, it should be noted that in about 30% of cases it is not possible to differentiate between NREM and REM dreams at all, in any of the many parameters mentioned here. These dreams will occur mainly towards awakening, in which the dreaming of each stage is at its peak. In other words, as the brain gradually "awakens" with the approach of waking up, the frequency of dreams increases and "slides" more and more from the REM stage to the other stages of sleep. As sleep continues, the dreams from each stage become longer, their vividness or realism increases and they are more likely to involve memories from distant times (for example from childhood).
Regarding the question we raised earlier, why a report of NREM dreaming arose following the change of the question, it is now possible to hypothesize the answer. Most of us have quite a wealth of experience in what characterizes dreams, based mainly on REM dreams, and it is possible that the different dreaming nature of NREM stages is not what we are used to calling a dream. Therefore, when the subjects were asked whether they had dreamed, they answered in the negative, even though it is possible that they were engaged in extensive mental activity before waking up.

I will briefly mention that there is a lively discussion among dream researchers whether REM and NREM dreams work in a similar brain mechanism or whether they are different mechanisms of action. Those who support one mechanism try to show that REM sleep is the main brain mechanism that allows dreaming and that dreaming in other stages actually occurs near the REM stage or temporarily activates REM mechanisms. On the other hand, other studies show that dreaming can disappear completely in cases of specific brain injuries (see photo #3) even though REM sleep and all its brain manifestations are completely normal. This discussion is too broad to detail in this article, but I will summarize and say that whether it is one mechanism or two, there is a consensus today among dream researchers that dreams can occur at any stage of the sleep stages. This fact suggests that dreaming is a very important part of brain activity. In part B we will try to give some of the reasoned answers that science provides to the question of why we dream, until then - pleasant dreams!

Thanks:
We would like to thank Nir Lahav from Bar Ilan University for his helpful comments, Rotem Lutz for her participation in the research and Prof. Thelma Hendler, Head of the Center for Brain Functions, for her support.
for further reading:
• The mind at night - the new science investigating how and why we dream / Andrea Rock. You spent with an employee.
• Yuval Nir et al.\ Dreaming and the brain: from phenomenology to neurophysiology, Trends In Cognitive Sciences 2009
• Psychology of dreams / Zvi Giora. Broadcasting University Press.
• Hobson J. Allan et al. \ THE COGNITIVE NEUROSCIENCE OF SLEEP: NEURONAL SYSTEMS, CONSCIOUSNESS AND LEARNING. Nature Reviews 2002

Appendix A: On lucid dreaming

A lucid dream is a dream in which the dreamers are aware of the fact that they are in a dream. Most people have experienced a lucid dream at least once or twice in their lives but only a minority report lucid dreaming more than once a week. In many cases, a lucid dream allows a certain control over the plot of the dream. The very knowledge that "it's just a dream" allows freedom of action and the ability to navigate the plot of the dream in contrast to ordinary dreams in which the plot unfolds as if by itself. Since the eye movements are active during REM sleep, voluntary eye movements can be used as a way to 'signal' researchers entering a lucid dream. Indeed, many studies have shown that lucid dreamers can control their eye movements and by a pre-agreed signal (for example five movements of the eyes from side to side) signal to the researchers that they are entering a lucid dream. A simultaneous recording of electrophysiological signals (with the help of EEG, see diagram no. 1) indeed indicated electrical activity that is characteristic of performing this task in burns. In terms of brain activity, the few imaging studies done on the subject show increased activity in the frontal and parietal lobes during lucid dreaming which can explain the increased awareness present during a lucid dream. Studies also show that it is possible to increase the frequency of lucid dreams with practice (see reference in further reading) and it is possible that this method has clinical potential in the treatment of disorders accompanied by repeated nightmares such as post-traumatic stress disorder (PTSD).

Appendix B: Sleep inertia
During deep sleep (stage 3, see diagram no. 1) brain activity decreases in a wide variety of areas, relative to cities. As a result, many of the areas we need for orientation, concentration or cognitive function are less active than usual. Thus, waking up from a deep sleep is a slightly confusing experience, leading to disorientation and lack of concentration and it takes time to 'recover' from it. This phenomenon is known as sleep inertia (in Hebrew: the persistence of sleep), since sleep seems to persist a little into wakefulness and takes time to dissipate. Studies show an impairment in the function of the subjects immediately after waking up from sleep which is manifested in a lengthening of reaction times, a lack of motor precision and a low mood. Sleep inertia can occur following awakening from any stage of sleep (sometimes even from an afternoon nap), but it is more significant upon awakening from deep sleep. The duration of the reaction varies depending on the stage from which the subjects woke up and the time of day, but it usually does not exceed about half an hour. Caffeine can accelerate the disappearance of sleep inertia by changes in specific receptors in the brain that are sensitive to fatigue.