Consciousness during sleep and the effect on the appearance of dreaming

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Consciousness during sleep and the effect on the appearance of

dreaming

Bachelor thesis

Nathasja Hartog

Supervisor: Prof. Dr. D.G.M. Beersma

Head of the Department of Chronobiology

Director of the Center for Behavior and Neurosciences University of Groningen

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Abstract

This study focuses on sleep and consciousness during sleep to see what the effect of consciousness is on the appearance of dreams and lucid dreams. Dreams seem to be experienced the most during REM sleep, but they also appear during non-‐

REM sleep. Thanks to neuroimaging, the activation and deactivation of brain areas during REM sleep has been made visible. The (de)activation of certain areas might give a possible explanation of some of the features of dreams, such as emotionality, lack of control and visual elements. Consciousness during sleep is an interesting factor, that also can be related to (de)activation of certain brain areas. Lucid dreaming is an interesting example of the coherence of consciousness and dreaming.

Keywords: Sleep, consciousness, REM, non-‐REM, dreaming, lucid dreaming, neuroimaging

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Introduction

Sleep and dreaming have always aroused our curiosity and theories as to their cause and function have been described since the beginning of recorded history.

In general people don’t remember what they dreamt of and this might be important for sleep’s functions. There are, however, people that do remember what they were busy with during their sleep. In general this isn’t a problem, but sometimes it can be a cause of sleeping problems. This might be good reasons to investigate the relation between consciousness and sleep more thorough.

Within this thesis sleep and its components will be discussed together with the component of consciousness during sleep. Dreaming is an interesting component of sleep and within this review it will be discussed together with the history of dream research, the possibility to recalling dreams and the neuroimaging of REM and non-‐REM sleep. The phenomenon of lucid dreaming will also be discussed.

All of these components form an interesting topic to look at, in my opinion.

I think that sleep research can give interesting points of view regarding the appearance of dreaming; not only when looking at the activation of brain areas, but also when analyzing dream reports. The standard features of dreaming (the components a dream standard consists of) are, as found, equal for everyone; I think that’s an interesting point to look at. These features, however, aren’t researched much until now.

Sleep

Sleep is a behavior that is displayed every day for a considerable amount of time.

Apparently sleep is important for us; but why is so little understood.

Phenomenologically, sleep can be described as a readily reversible state of reduced responsiveness to, and

interaction with, the environment (Bear et al. 2007, Dang-‐Vu et al. 2010, Czisch et al. 2004). It is known that sleep consist of two stages: Rapid Eye Movement sleep (REM sleep) and non-‐

REM sleep. Non-‐REM sleep is further classified into stages 1 (N1), 2 (N2), 3 (N3) and 4 (N3) according to the degree of EEG slowing (Rechtschaffen et al. 1968). These differences are shown in figure 1. In the figure EEGs during waking, during REM sleep and during the different phases of non-‐

REM sleep are shown. When looking at sleep, the time spent in a state can also be quantified: it is known that roughly 75% of total sleep time is spent in non-‐REM and 25% in REM.

The periodic cycles which are executed during the night last for about 90 minutes (Bear et al. 2007, Kajimura et al. 1999, Hobson 2009).

Figure 1: EEG rhythms during sleep (Bear et al.

2007)

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The periodic cycles thus consist of two states: non-‐REM sleep and REM sleep. In the following part of this thesis both non-‐REM sleep and REM sleep will be further defined and there will also be looked at the phenomenon of consciousness during sleep.

Non-‐REM sleep

Non-‐REM sleep seems to be the period of sleep for rest. Muscle tension throughout the body is reduced and movement is minimal, but during non-‐REM sleep muscles are not paralyzed (Bear et al. 2007, Hobson et al. 2000). During non-‐REM sleep consciousness is most likely to fade (Nir et al. 2010).

Non-‐REM sleep consists of compromising stages stage 1 (N1), stage 2 (N2), stage 3 and 4 (N3) (slow wave or delta sleep).

Stage N1 is characterized as the stage of sleep where the EEG is intermediate between wake and deep sleep, with presence of theta activity (4-‐7 Hz), occasional vertex sharp EEG waves and slow eye movements (figure 1).

Stage N2 sleep occurs throughout the night, where the EEG can contain spindles, K-‐complexes and occasional slow waves (figure 1). K-‐complexes represent slow biphasic waves of high voltage (Czisch et al. 2004).

Stage N3 occurs mostly early at the night (Dang-‐Vu et al. 2010, Nir et al. 2010, Bear et al. 2007) and it is characterized by spindles and slow high-‐voltage, EEG waves hence the name (Slow Wave Sleep) due to synchronized activity of neurons (figure 1) (Hobson et al. 2000, Nir et al. 2010, Hobson 2009, Maquet 2000).

Slow waves (Delta waves) are oscillations of cortical origin that have frequencies below 4 Hz; spindles are waxing and waning oscillations of thalamic origin that have frequencies around 12-‐15 Hz (figure 1) (Nir et al. 2010, Dang-‐Vu et al.

2010, Czisch et al. 2004).

REM sleep

REM sleep has been discovered in 1953 (Aserinsky et al. 1953) and it is also known as ‘paradoxical’ sleep, ‘active’ sleep or ‘desynchronized’ sleep (Hobson et al. 2000).

Contrary to non-‐REM sleep, REM sleep is considered as a state of high cerebral and low physical activation that would provide a neurophysiological marker of dreaming (Desseilles et al. 2011, Maquet 2000, Hobson 2009, Hobson et al.

2000) and REM sleep is also related to the homeostatic control of body temperature,

including the

temperature of the brain (Hobson et al.

2012).

REM sleep occurs mostly late at night and it seems to consist of an active,

hallucinating brain in Figure 2: REM sleep development. (Hobson 2009)

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a paralyzed body, which is characterized by movement of the eyes, fast low-‐

voltage EEG and low muscle tone; this evoked activity propagates much like it does during wakefulness (Nir et al. 2010, Hobson 2009).

REM sleep might act as a general “virtual rehearsal mechanism”, which would play an important function in the early brain development, congruent with the prominent presence of REM sleep in newborn babies and infants (figure 2) (Desseilles et al. 2011, Hobson 2009).

Both in animals and humans, REM sleep is believed to be generated by cholinergic processes arising from brainstem structures that mediate some widespread cortical activation via a ventral pathway innervating the basal forebrain and a dorsal pathway innervating the thalamus (Steriade et al. 2005, Maquet 2000).

REM sleep has been studied because it is the stage during which intense visual dream activity is most prevalent (Braun et al. 1998, Hobson 2009). REM sleep may present a state in which the brain engineers selective activation of an interoceptive network, which is dissociated from primary sensory and heteromodal association areas at either end of the visual hierarchy that mediate interactions with the external world (Braun et al. 1998).

Consciousness during sleep

Since primary sensory areas are connected to consciousness and REM sleep shows a dissociation of primary sensory areas, how can consciousness during sleep be defined? To start there are two types of consciousness: primary consciousness and secondary consciousness.

Primary consciousness can be defined as simple awareness that includes perception and emotion, where perception is defined as detailed visuomotor and other sense modality information that constitutes the representational structure of awareness. Such awareness must involve the interaction and integration of emotion (Hobson 2009, Hobson et al. 2012).

Secondary consciousness depends on language and includes such features as self-‐reflective awareness, abstract thinking, volition and metacognition (Hobson 2009, Hobson et al. 2012).

An interesting point of view might be that homeothermy may be necessary for normal consciousness; even small variations of brain temperature are devastating to consciousness (Hobson et al. 2012).

The level and nature of a person’s conscious experience varies dramatically during sleep; during slow wave sleep consciousness can nearly vanish despite persistent neural activity in the thalamocortical system (Nir et al. 2010, Hobson et al. 2000). It is useful to consider both similarities and differences between waking consciousness and dreaming consciousness and to relate these differences to changes in brain activity and organization (Hobson 2009, Nir et al.

2010). In this case, the differences between waking consciousness and dreaming consciousness are of interest the most..

Dreaming consciousness differs from waking consciousness by showing reduced attention and voluntary control, lack in self-‐awareness, altered reflective thought, occasional hyper-‐emotionality and impaired memory (Nir et al. 2010).

Perhaps the most striking feature of conscious experiences during sleep is how similar the inner world of dreams is to the real world of wakefulness (Hobson et

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al. 2000, Nir et al. 2010, Hobson 2009). The most obvious difference between dreaming and waking consciousness is the profound disconnection of the dreamer from their current environment; such disconnection is a key feature of sleep (it is also known as ‘high arousal threshold’) (Nir et al. 2010). In adult humans, dreams have features of primary consciousness but do not strongly evince the characteristics of secondary consciousness (Hobson 2009).

Dreaming

Dreaming: a phenomenon almost everybody has heard and one that everyone has experienced at least once in his or her live. But what is ‘dreaming’ and what is a ‘dream’?

Dreaming represents a major, universal facet of human experience that offers a unique view of consciousness and cognition (Desseilles et al. 2011, Hobson et al.

2000, Nir et al. 2010, Hobson 2009, Hobson et al. 2012). In the early decades of the psychoanalytic era, dreaming was regarded as the meaningful reflection of unconscious mental functioning (Palagini et al. 2011). The scientific analysis of dreaming is made somewhat prohibitive because the nature of the dream-‐state is highly subjective and a genuinely personal experience. Several theories include the affirmation that dreaming is a random by-‐product of REM physiology, which could possibly be related to some “unlearning” mechanisms in an otherwise overloaded brain (Desseilles et al. 2011, Hobson et al. 2000).

But other studies include that dreaming is a state of consciousness characterized by internally generated sensory-‐motor, verbal, cognitive and emotional experiences, which may unfold in actions and events forming imaginary plots (Desseilles et al. 2011, Nir et al. 2010, Hobson 2009, Marzano et al. 2011, Hobson et al. 2012). Dreams, similar to one’s personality in general, are quite stable over time in adulthood and they might share many characteristics across cultures (Nir et al. 2010). Emotional experiences in dreams are frequent, intense and possibly biased toward negative emotions. Probably all the categories of dream experience described are also subject to many alterations and distortions that are unlikely to occur in real waking life (Maquet 2000, Desseilles et al. 2011, Nir et al. 2010). Dreaming, especially in religious contexts, was thought to be a supernatural manifestation, and considered premonitory or prophetic (Palagini et al. 2011). Dream productive activity is submitted to unconscious and conscious processes (Cicogna et al. 2001, Hobson et al. 2012).

Findings suggest that REM sleep might reasonably be considered as a facilitating neurophysiological state for dreaming to occur, even though dreams are not exclusively experienced during this state of sleep (Desseilles et al. 2011, Nir et al.

2010, Hobson et al. 2012).

More recent models involve that dreams echo dynamic functions like reactivation and further consolidation of novel and individually-‐relevant features encountered during previous waking experience (Hobson et al. 2012, Desseilles et al. 2011) Such models of dreaming might be consistent with accumulating evidence showing the potential benefit of reprocessing freshly encoded information for long-‐term storage (Hobson et al. 2012, Desseilles et al.

2011, Hobson et al. 2000).

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In REM sleep, dreaming is characterized by the following remarkably consistent set of features (Hobson et al. 2000):

ü Dreams contain formed hallucinatory perceptions, especially visual and motoric, but occasionally in any and all sensory modalities

ü Dream imagery can change rapidly and is often bizarre in nature ü Dreams are delusional

ü Self-‐reflection in dreams is generally found to be absent relative to waking and it often involves weak, post hoc and logically flawed explanations of improbable or impossible events and plots

ü Dreams lack orientational stability

ü Dreams create story lines to explain and integrate all the dream elements in a single confabulatory narrative

ü Dreams show increased and intensified emotions, especially fear and anxiety ü Dreams show increased incorporation of instinctual programs

ü Volitional control is greatly attenuated in dreams

All these features can be found in REM dreams and most dreams during REM sleep contain a majority of these features (Hobson et al. 2000). Contrastingly, these features are rarely found in non-‐REM dream reports (Hobson et al. 2000, Maquet 2000, Perogamvros et al. 2012).

History of dream research

The first written record of dream interpretation came from the Egyptians around 1275 B.C. (Palagini et al. 2011). The first steps toward modern dream interpretation and their relationship to emotions were taken in the 5^th century B.C. when the Greek philosopher Heraclitus suggested that a person’s dream world was created within his own mind (Palagini et al. 2011). During this era dreams were thought to have prophetic properties (Palagini et al. 2011).

During medieval times theologians practiced a more careful, and to some extent more scientific, study of sleep and dream phenomena. Their interpretations, however, were still constrained by superstition and witchcraft (Palagini et al.

2011). Towards the end of the 1800s dream interpretation centered on the new psychological approach of psychoanalysis in which the content of a dream was analyzed to reveal its underlying or ‘latent’ meaning about the dreamer’s psyche (Palagini et al. 2011).

During the 1950s there was a turning point for the science of dreaming; an objective indicator of the dreaming state was discovered and a new cognitive approach to the phenomenology of dreams was developed (Desseilles et al.

2011). Since the 1970s several authors have shown that dreaming may promote the resolution of emotional conflict and reduce next-‐day negative mood (Desseilles et al. 2011, Palagini et al. 2011). Since the 1990s human brain imaging became a key player in the field of sleep research (Desseilles et al.

2011). Most modern dream research tries to relate neuronal activity retrospectively to dream form rather than to dream content; they focus on properties of all dreams rather than to investigate the neural correlate of a particular dream (Nir et al. 2010).

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Dream recall

Because of the development of brain research, it is now possible to investigate the phenomenon of recalling dreams.

According to Fell et al. 2006, the quantity of dream recall was found to correlate with functional coupling between rhinal and hippocampal cortices They measured the activity within these cortices during dream recall and looked at the correlation. They found that the coupling between these cortices led to better dream recall (Fell et al. 2006). Because the processing of declarative memories relies on these structures of the medial temporal lobe, increased interaction between those structures might be a key factor in determining declarative memory formation during REM sleep and thus increase dream recall (Desseilles et al. 2011, Fell et al. 2006). Memory is altered for the dream and within the dream; unless the dreamer wakes up, most dreams will be lost forever (Nir et al.

2010, Fell et al. 2006). Most children and young adults remember their dreams at least sometimes (84%), only 5% reported no dream recall at all (Voss et al.

2012). It seems to be that girls have a slightly, but significantly, higher recall of their dreams (Voss et al. 2012).

Dream reports contain a variety of sensations across different modalities: the most prevalent are vision (nearly 100% of all dreams contain at least one visual element) and audition (40-‐60%), while movements and tactile sensation (15-‐

30%) and smell and taste (less than 1%) are less frequent (Desseilles et al. 2011, Nir et al. 2010). The neurocognitive model claims that dreams are internal narratives; unless internal experiences are tied to external cues (i.e. times and places) they are bound to be forgotten (Nir et al. 2010). Dream recall was significantly correlated with frequent lucid dreaming (Voss et al. 2012).

Not only after awakening from REM sleep, but also after awakening from non-‐

REM sleep dream recall is obtained, with some differences in the frequency and content characteristics (Marzano et al. 2011, Hobson et al. 2000, Maquet 2000).

A positive relationship of both word count and subjectively estimated dream duration with the length of preceding REM sleep exists (Hobson et al. 2000). Reports from REM sleep awakenings are longer, more perceptually vivid, more motorically animated, more emotionally charged and less related to waking life than reports from non-‐REM awakenings (Hobson et al.

2000). In contrast to REM sleep reports, non-‐REM sleep reports contain thought-‐like

mentation and

representations of current concerns more often than do REM sleep reports (Hobson et al. 2000). In figure 3, the tomographic distribution of correlation values (rho

Figure 3: tomographic distribution of brain activity (Marzano et al. 2011)

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values) between the actual number of dreams recalled after morning awakenings with the amount of theta activity in REM sleep (top of the figure) and with alpha activity in stage 2 non-‐REM sleep (bottom of the figure) are shown (Marzano et al. 2011). The values are expressed in terms of rho values: positive rho values indicate the presence of a positive correlation and vice versa. The maps are based on 19 unipolar EEG derivations of the international 10-‐20 system with averaged mastoid reference (Marzano et al. 2011).

Neuroimaging of REM sleep

Neuroimaging studies, using PET and fMRI, have shown that the distribution of brain activity during REM sleep is not homogeneous, which provides important insights into the putative cerebral underpinnings of dreaming (Desseilles et al.

2011, Hobson et al. 2000). Unlike PET, fMRI allows repeated, non-‐invasive and high-‐resolution measurements of functional changes in the human brain (Desseilles et al. 2011). An advantage, for example, is that with help of fMRI correlations between spontaneous eye movements and regional cerebral blood flow in the cortices and thalamus have been found (Desseilles et al. 2011).

However, fMRI is associated with some constraints that make this method relatively complicated for sleep studies (Desseilles et al. 2011).

Early neuroimaging data confirmed the sustained neuronal activity observed with EEG, by showing a high-‐level of cerebral energy requirements and a widespread increase of cerebral blood flow during REM sleep (Desseilles et al. 2011, Hobson et al. 2000). Compared to wakefulness and non-‐REM sleep, REM

sleep is

characterized by a specific pattern of

brain activation (Desseilles et al. 2011).

During REM sleep in humans, compared to wakefulness, a significant increase in regional brain activity has been found in the following brain areas: Pontine tegmentum, Thalamus, Basal forebrain, Anterior cingulate cortex (ACC), Limbic and paralimbic structures, including Amygdaloid complexes and Hippocampal formation (figure 4) (Desseilles et al. 2011, Braun et al. 1998, Nir et al. 2010, Marzano et al. 2011, Dang-‐Vu et al. 2010, Hobson et al. 2000, Maquet 2000).

Activation of these regions suggest that memory consolidation processes, in particular emotional memories, may occur during REM sleep (Desseilles et al.

2011).

Figure 4: Functional neuroanatomy of human REM sleep (PET study) (Desseilles et al. 2011)

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Several motor regions are activated during REM sleep, including primary motor and premotor cortices, as well as the cerebellum and basal ganglia. These results are in line with the motor content of dreams (Desseilles et al. 2011).

Braun et al. (1998) found that, during REM sleep, activation within the temporo-‐

occipital regions showed some functional dissociation. The activation of the extrastriate cortex (visual association areas) significantly correlated with the deactivation of the striate cortex (primary visual cortex) during REM sleep (Braun et al. 1998).

The correlation between these regions is given in figure 5; the more active the extrastriate cortex is, the less active the striate cortex is. In figure 5A, REM sleep is compared to wakefulness; within this figure the correlation between the lateral occipital cortex and the striate cortex is given. In figure 5B, REM sleep is compared to Slow Wave Sleep; within this figure the correlation between the inferotemporal cortex and the striate cortex is given during REM sleep compared to Slow Wave Sleep.

Activity in both regions is usually found to be positively correlated during wakefulness (Braun et al. 1998).

Several regions are significantly hypoactive during REM sleep when compared to wakefulness. The regions that are significantly hypoactive are in particular: the Dorsolateral prefrontal cortex (DLPFC), Orbitofrontal cortex, Posterior cingulate gyrus, Precuneus and the Inferior parietal cortex (figure 4) (Desseilles et al. 2011, Dang-‐Vu et al. 2010, Czisch et al. 2004, Maquet 2000, Hobson et al. 2000). Besides these regions, other regions also are hypoactive compared to wakefulness, but not this significant. Maybe the hypo-‐

activity of these brain regions play an important role in dream amnesia (Nir et al.

2010, Maquet 2000).

Neuroimaging of non-‐REM sleep

Neuroimaging studies also strongly support a distinction between REM and non-‐

REM sleep as states whose differing neuroanatomical activation patterns predict their observed phenomenological differences (Hobson et al. 2000). Several studies on cerebral metabolism during sleep have indicated that global cerebral energy metabolism is decreased during non-‐REM sleep (Andersson et al. 1998, Hobson et al. 2000); global blood flow compared to wakefulness, however, didn’t seem to be affected by sleep (Andersson et al. 1998). PET and fMRI have consistently found a drop of brain activity during non-‐REM sleep when its activity is compared to wakefulness; this decrease has been estimated at around 40% during slow wave sleep compared to wakefulness (Dang-‐Vu et al. 2010, Palagini et al. 2011). The reductions in activity were located in subcortical regions (the brainstem, thalamus, hippocampus, basal ganglia and basal

Figure 5: Correlation between extrastriate cortex and striate cortex.

A shows REM sleep compared to wake, B shows REM sleep compared to SWS (Braun et al. 1998)

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forebrain) and cortical regions (the prefrontal cortex, anterior cingulate cortex and precuneus) (Hobson et al. 2000, Palagini et al. 2011, Dang-‐Vu et al. 2010, Andersson et al. 1998).

Lucid Dreaming

Since this thesis is about the consciousness during sleep and the effect on the appearance of dreaming, lucid dreaming is an extremely interesting kind of dreaming.

Lucid dreaming is the experience in which the dreamer is conscious of being in a dream (Cicogna et al. 2001, Voss et al. 2009, Hobson 2009, Voss et al. 2012) and, to some extent, capable of modifying the content of the ongoing dream (Voss et al. 2009, Voss et al. 2012). The occurrence of lucid dreaming in adulthood is rather rare and difficult to maintain (Voss et al. 2012). Several authors have reported an inverse relationship of age and frequency of lucid dreaming: lucid dreaming occurs primarily in childhood and puberty (Voss et al. 2012). Frequent lucid dreaming occurs most often before the age of 17 years, incidence rates seem to remain at similar levels until the age of 13 years, after which it steadily declines. Older students (ages 17-‐19 years) appear to experience lucid dreams only very infrequently (Voss et al. 2012). EEG findings indicate that lucid dreaming might correspond to a hybrid state of consciousness, with some EEG features similar to wakefulness and some to REM sleep; with the rare but instructive co-‐activation of both primary and secondary consciousness circuits (Voss et al. 2009, Hobson 2009). Some studies have shown that it is possible to let the participants signal lucidity by horizontal eye movements (Voss et al. 2009). As shown in figure 6, the eye movement signals (EOG) are recorded for three different states: Waking with Eyes Closed (WEC), Lucid and REM sleep.

The EOG refers to two channels, one for each eye as indicated by the separate colors.

Eye movements in lucid dreaming are systematic, repetitive and more pronounced than in REM sleep (Voss et al. 2009). Low EMG (figure 6) is found in lucid dreaming and REM sleep, highlighting the muscle relaxation common to both states (Voss et al. 2009).

Quantitative EEG studies comparing brain activity during waking, lucid dreaming and REM sleep show a difference in activity of the brain. Frontal areas are highly activated during waking but show deactivation during REM sleep (figure 7).

During lucid dreaming there is an increase in 40 Hz power and coherence in frontal areas compared with non-‐lucid REM sleep/ In lucid dreaming additional electrical activation of the brain is needed to activate the dreamer’s forebrain

Figure 6: Signaling lucidity (Voss et al.

2009)

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enough to recognize the true state without causing

waking and thus

terminating the dream

(Hobson 2009).

Differentiated regional activation (figure 7) may

underlie the

phenomenological

distinction between the

states REM sleep, lucid dreaming and waking; scale bars indicate standardized power based on scale potentials (Hobson 2009).

Conclusion/Discussion

When looking at all the components of sleep, consciousness and dreaming there can be concluded that all of these show a clear coherence. Sleep is a phenomenon that, in general, everybody experiences every night. Consciousness and dreaming seem to be related to each other, but the exact relationship between these two components is not yet clear. Lucid dreaming is an interesting example of the coherence of consciousness and dreaming, but also in this case still a lot has to be done.

Dreams seem to be experienced the most during REM sleep, but they also appear during non-‐REM sleep. Thanks to neuroimaging, the activation and deactivation of brain areas during REM sleep has been made visible. The (de)activation of certain areas might give a possible explanation of some of the features of dreams, such as emotionality, lack of control and visual elements.

The secondary aspects of consciousness rarely appear during dreams. And if they appear, it will most likely be in the dream of a child; lucid dreaming is an example of this. The appearance of secondary consciousness during dreaming (e.g. being aware of dreaming) might be artifacts that only appear under special conditions, e.g. brain development in children. If this were true, the absence of secondary consciousness during sleep would be a normal, healthy situation.

Consciousness would be active again during wakefulness, when sensory information begins to play a role again.

When looking at brain activity, certain brain areas have to be active when waking but not/less active during sleep. The interpretation of what happens in the brain and the behavioral reactions that would appear when wake, have to be diminished. If this were not the case, one would jump out of his/her bed for even the slightest thing. This means that is would almost be necessary not to know what you think during your sleep to have a good night rest.

When looking at all of the authors and studies I have used, I think I have seen a lot of different views regarding sleep, consciousness and dreaming.

Allan Hobson seems to be an important person within the dream research, but I do think that some of his claims are a little odd. Sometimes he tries to convince his readers of the necessity of dreaming. If dreaming really was necessary, I think also adults should remember what they dreamt of. Children often do

Figure 7: Comparison of activity during different stages (Hobson 2009)

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remember what they dreamt of, but they don’t seem to rate this at high importance.

The studies of Ursula Voss, I really liked, because they double-‐checked everything. For example with the questionnaires, students executed them with the children that participated, because students are ‘closer’ to children than professors are. Besides this they also used antipodal questions; if a child answered ‘yes’ on the first question, it had to answer ‘no’ on the next one.

Voss et al. used large experimental groups, so outliers wouldn’t conflict the data too much.

I also used some reviews; these articles gave an overview of a big number of studies. I think the reviews were a good source of information, because it gave a good overview without a too obvious opinion in it.

I found two types of researchers: the ones with a clear view that will use all the date they can to proof they’re right and the ones that are curious and willing to change their view for a different one of the data need them to do so.

I think that Hobson is an example of the first type of researches and Voss of the second type.

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Consciousness during sleep and the effect on the appearance of dreaming