by Zeev Nitsan
Assumptions regarding the survival advantage of this neural network, which is also proved to exist in animals’ brains, are related to simulations inspired by it and enables the preparation of the brain for “real situations.” According to another assumption, the network is a type of a “field court-martial” of the perception impressions that perform a sort of selection (i.e., determines which of the perceptual impressions will be further processed and which will be abandoned and dissipate) according to the level of importance to the perception of the self.
The default mode in which we are in a weak interface with reality manifestations, in a type of daydreaming, is the comfort zone our thoughts tend to wander to, more and more, as we grow older.
At an old age, our brain is more prone to “attention leakage”; it is more easily distracted and becomes more “flooded.” The difficulty of ignoring distracting information that constitutes “white noise” probably derives from the fact that the “enforcement” of attention that takes place in the frontal lobes is less rigid and enables “attention blinking” and division of attention. Then, the brain tends to get lost in the paths of the daydreaming kingdom. But some people believe that the loosening of attention enforcement is actually an advantage; the wandering of thoughts enables, at certain times, divergent thinking and a more comprehensive review of the situation.
Some claim the changing level of wakefulness of the neural network system of default inducts a tendency to use certain behavioral patterns that cause the variation in our response to different stimulations of the external world. At different times, we tend toward extrovert or less extrovert behaviors in accordance with the background voices of the default system. Its activity, which was once hidden, is actually the part of the puzzle that was missing in the past, and its absence often made our reactions seem chaotic. The fluctuations in the level of activity cause certain changes in our responses, which is one of the reasons our brain can be compared to the river in Heraclitus’s fable.
Through active tracing of the function of the default system, researchers managed to predict when a certain individual was about to make a mistake in a computerized test more than thirty seconds before the mistake was actually made. The tendency to make the mistake was formed when the default system “took control,” and, at the same time, the attention beam, which was supposed to remain focused in order to meet the challenge, was scattered.
It seems that we are dealing with a sort of a mix, and only at rare points our attention pendulum turns sharply and “magnetizes” to a single end—of internal focus or an external one. It seems that at every given moment, the pendulum is somewhere between these two observation posts.
The ability to choose the object of attention and remain focused on it often lessens with the ascent in the years’ mountain as we grow older. The stimulations of the external world tend, then, to become more invasive and distracting.
The function of the default system constitutes a supportive garden bed for the germination of raw thinking seeds, and it seems that it has an important role in maintaining the quality of brain function. It might also shed a different light on the tendency of many who consider daydreaming a waste of time. It seems that sometimes it is better to be a bench player in the game of life, since the “bench insights” might come in handy when we go back to the noisy court.
The Mirror Reflecting the Image of the Self
Some ascribe the origin of the “self,” the preserving of its identity, and its adjustment to the changing circumstances- to the activity of the default system. According to this approach, the default system is the structural and functional basis of the sense of self-identity. The supposition is that the system preserves a basic pattern of the “self,” which is available to us so we do not have to reevaluate time and time again the contents of our self-identity: our memories, values, beliefs, expectations, etc. The eternal flame of the “self” is preserved within the function of the default system. It is like a mirror that constantly reflects the image of the self, and the sense of continuity is preserved due to the constant function of the system.
The Structural and Functional Basis of the Default System
The structural-functional level of the default system relies on areas that are close to the brain’s midline. These are mainly the central areas of the parietal lobes, where massive activity takes place whenever a person reminisces about the past, and of the frontal lobes, whose role is, inter alia, to attempt reading other people’s thoughts. Activity at these areas, which testifies to the function of the default system, was also observed in the brain of people under preoperative general anesthesia and, also, during light sleep.
The Functional Infrastructure—Superconductor of the Frequencies Band?
The bioelectrical, or electrochemical, signals system in the brain spreads across a wide continuum of frequencies in a range that goes from a low frequency of a single signal per ten seconds (a frequency of one-tenth hertz) to signals whose frequencies are more than one hundred signals per second (more than one hundred hertz).
The chaos in the transportation channels in the brain is prevented due to the priority certain rhythms of signals have over others, as in a hierarchical range. According to a popular assumption, the default system is at the top of the range, and it functions as a frequencies synchronizer. This system functions as the super-conductor of the frequencies band.
The oxygen consumption of the neural network of the default system swings slowly once in ten seconds, approximately (one-tenth hertz frequencies). Such a low frequency was also found in the electrochemical activity of the cortex. It is assumed that it reflects the basic rhythm of the default system. According to this, rhythm acts as the super-conductor’s baton in the brain’s frequencies band, and it serves as the reference oscillator, or Greenwich point, of frequencies of the brain.
When the Default System Fails
The function of the default system is disrupted among those who suffer from various neurological diseases. Such a disruption was observed in the diseases of Alzheimer’s, schizophrenia, depression, autism, and post-traumatic stress disorders. The disruption patterns related to the function of this network vary across different neurological disorders. Thus, for instance, among people who suffer from attention disorder, the attention pendulum tends toward the end of over-focus when external stimulations are present, and, accordingly, the activity of the default system in their brain is lower.
It was found that in the brain of people who suffer from schizophrenia, on the average, the connections between brain areas that constitute the default system do not function properly and the entire system is overactive. As a result, the ability of those who suffer from schizophrenia to focus and react to external reality is compromised. The internal stream of consciousness in their brain is dazzled by inner lights that cast a shadow over the occurrences of external reality.
It was also found that the system is overactive among people who suffer from depression, and attention dedicated to a certain external task tends to slide back to the dominant activity of the default system. Another finding was a lower-than-average connectivity between the areas of the default system and areas in charge of motivation and reward-oriented behaviors. This might be the source of anhedonia—the lack of a sense of pleasure, which characterizes inter alia, a depressive condition. At the same time, the system is overly linked to emotion-stimulating areas. It might provide an explanation for oversensitivity among those who suffer from depression.
Among researchers who study the default system in relation to depression, there is controversy concerning the cause and effect. Are those who tend to daydream more prone to become depressed? Or is it the other way around: depression leads to scattering of thinking and daydreaming?
These findings support the possibility of observing the system’s function as a diagnostic tool. A glance at the brain when it is “on vacation” might enable us to assess whether a disease such a depression is being formed in the brain and, if so, what the level
of severity is. Remedial interference might help improve the condition of those who suffer from cerebral syndromes related to this neural system.
Memory in the Moonlight
A great part of the enigma related to the role of sleep is still in the dark, but there are multiple pieces of evidence that point to the importance of sleep with regard to information assimilation and memory preservation.
Numerous studies show that during sleep information that has recently been captured is being consolidated in our memory, and new skills are being formed into the neural infrastructure that encodes them. At critical developmental periods, sleep is essential for creating a web of neural maps that represent skills that have been learned recently. During an average night’s sleep we experience four to five sleep cycles that last approximately ninety minutes each. In each sleep cycle, we move from superficial sleep (stage 1 and primarily stage 2) through deep sleep (stages 3 and 4) to REM (rapid eye movement) sleep.
Brain-wave frequency at the deep sleep stage (stages 3 and 4 of the sleep cycle) is mainly at the range of the delta waves, which are characterized by low frequency and high amplitude. In addition, the waves’ activity at these stages is regulated and synchronized. These stages tend to take place at the first half of the night and often in proximity, in time, to falling asleep. Deep sleep, which is reflected in brain waves, whose frequencies are even lower than the frequencies characterizing superficial sleep, was found as essential for the activity of the hippocampus and for encoding the information our brain is exposed to during wakefulness. Decrease in the duration of deep sleep stages compromises our ability to assimilate new information. In the aging brain, deep sleep stages become shorter and shorter and sometimes even absent altogether. It seems that it is related to the decreased ability of the aging brain to assimilate new information.
In an experiment, a ring was heard at the points where the participants moved from superficial sleep to a deeper sleep, and, accordingly the frequency of their brain waves became lower. The ring woke them up and made them start a new sleep cycle over and over, and, in fact, prevented them from reaching the deep sleep stages. As a result, their memory performance was worse than before, and a functional MRI test showed decreased hippocampus activity. These findings supported the assumption that deep sleep is highly important to encoding new information.
We touch our memories with the fingertips of dreams. It seems that the REM stage, like deep sleep stages (slow wave sleep), contributes to turning short-term memories into a more durable neural web, which actually makes them long-term memories.
One challenging hypothesis that came up in the circles of sleep researchers was that the dreams are like “dustbins” of memories. According to this view, memories are consolidated during REM sleep, and those that are about to be deleted appear briefly in our dreams on their way to oblivion, and this is why we tend to forget our dreams. Nowadays, there are not many supporters for this view.
The Corridor of Experience—between Sleep and Wakefulness
At both ends of night, when we are half asleep, we experience unique modes of consciousness. When the influence of the arrows of Hypnos (god of sleep) has not yet fully diluted in our blood and has not yet fully taken control over our brain, we experience the hypnogogic state. At the other end of the night, when the effect of Hypnos’s arrows starts to expire, we experience another unique mode of consciousness—the hypnopompic state. It seems that these are the times when we are at the edges of awareness. Upon awakening, the transition from the sleep-awareness state to the wakefulness-awareness state is gradual and provides a sort of “corridor” characterized by rare awareness states. When we wake up in the morning, the dream narrative is often cut off, and the self-system usually needs a few moments of grace to initialize itself. The self-model does not appear fully on the screen of consciousness, and we are at a stage that might be defined as “partial self.” At this state, we feel a little confused and disoriented, and it lasts until the restart of the self-model is completed and it reappears, with all its glory, on the screen of consciousness.
The twilight zone between sleep and wakefulness presents a rare opportunity for us to glance through the porthole at the activity pattern of the consciousness.
Thoughts From the Borderland Between Sleep and Wakefulness
“Thought bewilderment” upon waking up (hypnopomp), before the self-model has had the chance to initialize itself and buy back the golden share of our brain and, at the other end of wakefulness, thought bewilderment prior to falling asleep (hypnagogia) are fertile sources of unique thinking.
The writer Robert Louis Stevenson said that many of his stories were based on hypnogogic visions, including his famous story of the divided self, The Strange Case of Dr. Jekyll and Mr. Hyde (1886), which was once described as a story whose basic plot thread was weaved at the junction between wakefulness and sleep.
Between Reality and Dream
Do dreams are a different reality? Or are dreams and reality pages in the same book? This question is ascribed to philosopher Arthur Schopenhauer.[8]
The thin line between dreams and reality is illustrated in a joke about a person who woke up startled from a dream in which he lost ten gold coins. A few minutes later, he came to his senses and decided to go back to sleep so he could search for the ten lost gold coins and find them.
There is also the familiar story from China about a person who dreamt that he was a butterfly. Upon waking, he started wondering whether he was a butterfly in a person’s dream or whether what he thought of as a dream was actually the real reality and now he was actually a human being in a butterfly’s dream.
In Lewis Carroll’s book Through the Looking-Glass, Tweedledee and Tweedledum try to convince Alice that she is merely a character in the red king’s dream and at the moment the king, who sleeps throughout the story, wakes up, her existence will end at once. Since Alice herself dreams the entire story, the red king is actually a character in her dream, as she is a character in his. This can be referred to as a dream within a dream within a dream—a recursive, multireflection picture.
At the “dream theater” that hosts a new performance behind our eyelids every night, we are the producers, directors, and stage workers. In this sense, studying the dreaming brain presents a keyhole through which we can glance at the backstage of the brain theater. On the other hand, we are also the viewers and the critics of the performance being performed at the hall of our skull.
Studies have shown that we remember approximately 5 percent of the dreams that visit us. Conscious dreaming is a state in which a person gains control over the plot of the dream—he is aware of the fact that he is asleep and dreaming. There are psychological methods, such as frequent reality testing during night sleep, that lead to an ability to be located in this unique consciousness mode. Conscious dreamers are called lucid dreamers, and, once their skill is improved, they are able to consciously, and in real time, write down part of the scenario of the plot of the dream theater that is unfolding in their brain.
According to a scientific article, when we dream about ourselves there is a certain age limit we never pass. It might be our ego that tries to upholster itself with pillows for prevention of shocks during sleep.
Dreamy Activity
Brain scans shows that while we dream intense activity takes place, primarily at brain areas in charge of processing raw instincts and emotions such as the libido and the aggression instinct.
At the same time, there is less activity in the cortex of the prefrontal lobe, which is in charge of regulating emotions and channeling raw instincts into more subtle, restricted paths. Thus, at time of dreaming, our brain is mainly motivated by raw emotions and instincts that are not given the polished touch by the prefrontal cortex. In this sense, dreams can serve as a window to the primeval basis of our being.
The Brain Under the Stars’ Light, or Who is Not Sleeping While We are Asleep?
When the lullaby of Hypnos (god of sleep in Greek mythology) envelops our b
rain and makes us fall asleep, our brain enters a different functional mode. Even when we are asleep, however, certain areas remain active in our brain, which is like a “city that never sleeps.”
When Morpheus, the god of dreams, visits us every night at the REM stage, our brain experiences a wakefulness-like mode in terms of the electrical rhythm, as reflected in electroencephalogram (EEG) test. While our eyelids are fluttering, our brain is dipping in the pool of neurotransmitters, which is characteristic of the dream stage of the “night swim.” During the REM stage, the amount of dopamine in the brain is reduced and the amount of acetylcholine increases. At the same time, the muscle tone declines. This mode of sleep is characterized by high-frequency, low-amplitude beta waves similar to the state in intense wakefulness. The duration of the REM stages gradually increases as sleep progresses, and most of them take place during the second half of the night. The average duration of REM sleep changes in different periods of life. In the brain of a newborn, who has just emerged in our world, dream sleep constitutes about 80 percent of the overall sleep time, while in the brain of an adult it constitutes about one-quarter of the whole sleep time.
