Default State (Network) & Altered States

[마황]

Default State (Network)
 A common perception (or misperception) about a resting brain is to assume that it is doing nothing. But according to PET scan (in the old days) and fMRI scan on hundred of volunteers, whenever the brain is not working, it switches to some kind of internal processing with a lot of activities in the prefrontal cortex and hippocampus (Figure 32). One theory likens it to daydream with a very serious purpose - for incorporating lessons learned in the past (by activating the hippocampus) into our plans for the future (using the higher function in the prefrontal cortex), such process is called default network. The association of default network with very slow brain wave (0.1 Hz or less) even in sedated humans and heavily anaesthetized monkeys lead to suggestion linking it with sorting and preserving memories. Since it devours huge amounts of glucose (used up 30% more energy than other area of the brain) in the process and its impairment is related to many brain diseases, it must be very important whatever function it serves. BTW, the brain seems to go into a truly resting state via meditation, which deliberately turns off the default network. Such feat actually requires a lot of training and is not easily attainable.
 

Figure 32 Default State

Altered States

 It is not possible to divide states of being into the neat categories of consciousness and unconsciousness. Too many curious and interesting states lie between, challenging a simple definition. These altered states of consciousness defy objective description because they are intensely personal. Nevertheless, these experiences, which range from the mild distraction of a daydream to wild, drug-induced hallucinations, can have certain common characteristics related to the change of perceptions of the self and the outside world. The term "altered states" covers a number of phenomena. Some arise naturally and automatically (dreaming, for example,
 

is thought to be common to all mammals). Others are attained through learned techniques such as meditation. Some are induced by drugs. Other still - the vision and trance states - are highly controversial, and many people doubt their existence. To understand altered states one must assess subjective accounts of what it is like to "be in" these states, along with objective research that tries to identify their physiological basis and effects. Figure 33 shows the brain scan for some of the altered states listed below. The areas in light blue color represent over-activity in the upper row, while the same color indicates under-activity in the lower pictures.
 

Figure 33 Altered States

•Dreaming - Vivid visual dreams light up the visual cortex; nightmares trigger activity in the amygdala and the hippocampus flares up from time to time to replay recent events. The areas, which seem to be most commonly active are the pathways carrying alerting signals from the brainstem and the auditory cortex; supplementary motor area and visual association areas - all of which produce the "virtual reality" effect of dreaming. Activity is decreased in the dorsolateral prefrontal cortex, the area of waking thought and reality testing (Figure 33). Studies have shown that dreaming sleep occurs in a wide range of animal species. Figure 34 shows a dreaming cat. When its pons is surgically removed to permit movement during REM sleep, the very nice cat becomes a vicious tiger when it is dreaming and throws itself at imaginary prey. 
 

Figure 34 Dreaming Cat

•Daydream - Many surveys suggest that ordinary men and women, who are neither disturbed nor neurotic, spend a large part of each day in some sort of fantasy, reverie or daydream. This kind of quick fantasy rarely has a structured narrative. It is the moment when we stop paying attention to what we are seeing and hearing and switch into an inner theatre of the imagination where we can play at wish fulfillment (Figure 35). But there are other fantasies qualitatively different from these "wouldn't it be nice if ..." stories. These are sustained fantasies, which often seem to have been crafted, worked and reworked to meet some more profound psychological need. When one daydreams, normal inhibitions are bypassed. The evidence of the rather macabre biographies of serial killers shows that they had frequently recurring violent fantasies before they turned to murder.

Figure 35 Daydream

•Meditation - One function of consciousness is to knit together our sense of self-identity. But many religious traditions believe that enlightenment can be achieved only by breaking the shackles of self and attaining "purer" states of consciousness through meditation (Figure 36). As well as its psychological benefits, the meditative state has marked physiological effects - these phenomena are measurable and reliably repeatable, and thus are a suitable object of scientific study. Such studies have revealed some remarkable effects: meditation can lower a subject's metabolic rate, decreasing blood pressure, pulse rate and muscle tension. One study shows that the subject could reduce his oxygen intake to one-third of the normal resting state. Scans of people in a self-induced state of "passive attention" have been shown to "turn off" areas of the brain normally associated with seeking stimuli, including the parietal, anterior and premotor cortexes (Figure 33).
 
•Hypnosis - Modern studies show that the brain waves of hypnotized subjects are much like those of the waking state. When subjects are hypnotized, they can speak, walk and carry out instructions. Yet there are some noticeable changes from normal consciousness: attention becomes very selective, with the subject ignoring everything but the hypnotist's voice; the subject rarely initiates thought or activity, but waits for suggestions from the hypnotist; and fantastic ideas or situations are more readily accepted as reality. It is almost as if the willing, relaxed subject relinquishes control over part of his or her consciousness to the hypnotist. The classic method of hypnotism is to put a subject into a relaxed frame of mind and ask him or her to concentrate on an object, such as a swinging pocket watch (Figure 37). Brain scans (Figure 33) show increased activity during hypnosis in the motor and sensory areas suggesting heightened mental imagery. Increased blood flow in the right anterior cingulate cortex indicates that attention is focused on internal events. The brain activity seen in this state is quite different from that seen in normal waking or sleeping.

 •Sexual fantasy - This is the ability to use our imaginations erotically. It is found that people spend a surprising amount of time thinking about sex. There are vast cultural differences in what different societies consider acceptable material for sexual fantasy and fetishes. The Victorians considered fetish to be shocking and dangerous, the true dark side of sexuality; while the Freudian view treats fetishism as the result of linking unresolved childhood drives to object that seems "safe" such as the high-heeled shoe. Many therapists now consider that it is perfectly normal to have sexual fantasies, and some even believe that they can be used to achieve a more fulfilling sex life. Research into sexual fantasies is complicated and must rely on what patients report to their therapists, but some studies have found links with childhood events - either sexual violence or a strict, repressed upbringing. There is an obvious distinction between fantasy and action - a fantasy does not harm others. However, some people who have fantasies that involves inflicting pain to themselves or others (such as to the cat in Figure 38) claim that they feel compelled to act them out. Sometimes people with less extreme fantasies also choose to turn them into realities such as in the form of cross dressing.

•Addiction - Drug addiction is caused by a similar train of events to hunger. However, unlike most types of food, addictive drugs cause changes in the receptors to which they bind, making them less sensitive. This creates tolerance and addiction. Most addictive drugs work by altering levels of neurotransmitters in the brain's reward circuitry centered on the limbic areas. Other brain areas are also involved and each type of drug works in a slightly different way to produce its characteristic effects. Opiates are drugs derived from the dried resin of the opium poppy (Figure 39), or synthetic versions of these chemicals, such as heroin, codeine and morphine. All have been used medicinally at some time for their pain-killing properties. They are used illegally for similar reasons: heroin gives the user a "high", reducing anxiety and producing a sense of temporary well-being.

•Schizophrenia (shattered mind) - There is evidence to suggest that genetic vulnerability and environmental stressors can act in combination to cause schizophrenia. Some researchers estimate schizophrenia to be highly heritable. But a recent review of the genetic evidence has suggested only a 28% chance of one identical twin developing schizophrenia if the other already has it. A recent study listed seven genes as likely to be involved in the inheritance of schizophrenia or the risk of developing the disease. One of these genes known as COMT is involved in encoding the dopamine catabolic enzyme. This is interesting because of the known link between dopamine function, psychosis, and schizophrenia. There is considerable evidence indicating that stressful life events cause or trigger schizophrenia psychosis. Childhood experiences of abuse or trauma have also been implicated as risk factors for a diagnosis of schizophrenia later in life. There is also consistent evidence that negative attitudes towards individuals with schizophrenia can have a significant adverse impact. In particular, critical comments, hostility, and intrusive or controlling attitudes from family members have been found to correlate with a higher risk of relapse in schizophrenia across cultures. Factors such as poverty and discrimination also appear to be involved in increasing the risk of schizophrenia or schizophrenia relapse, perhaps due to the high levels of stress they engender. The disease is frequently accompanied by paranoia and delusions. Some may experience extremely bizarre hallucinations. Ironically, while some areas of the schizophrenic brain may be dead, in other ways the sufferer's brain is overactive. Most schizophrenics appear to have an excess of dopamine in the brain, the neurons become overloaded and relay inappropriate messages (see Figure 40 for a modern view). Lack of activity in the frontal lobes is a feature of states of mind in which consciousness is disturbed. This might account for the state's common reduction in planned or spontaneous behavior and social withdrawal. The anterior cingulate cortex - thought to distinguish between external and internal stimuli - is also underactive (Figure 33), which may be one reason schizophrenics confuse their own thoughts with outside voices. Recently in 2006, it is found that those with mutations in the PCM1 gene had a significantly lower volume of grey matter in their orbitofrontal cortex resulting in poor judgement, inappropriate social behaviour and not keeping themselves clean. PCM1 plays a role in cell division, which in the brain occurs more actively at adolescence - an age at which schizophrenia is commonly diagnosed. 
 

Figure 40 Schizophrenia

•Dementia - Dementia is used to describe the organic deterioration of the brain that affects the elderly. The main, but not sole, form of dementia is Alzheimer's disease, and 25 percent of people who live to be older than 85 will show some symptoms. One of the hallmarks of Alzheimer's disease is the accumulation of amyloid plaques between neurons in the brain. Amyloid is a general term for protein fragments that the body produces normally. In a healthy brain, these protein fragments would be broken down and eliminated. In Alzheimer's disease, the fragments accumulate to form hard, insoluble plaques blocking signals from reaching the receptors. Neurofibrillary tangles consist of insoluble twisted fibers that are found inside of the brain's cells. They primarily consist of a protein called tau, which forms part of a structure called a microtubule. The microtubule helps transport nutrients and other important substances from one part of the nerve cell to another. In Alzheimer's disease the tau protein is abnormal and the microtubule structures collapse (this is the 2nd stage). There is an overall shrinkage of brain tissue as Alzheimer's disease progresses. In addition, the ventricles are noticeably enlarged. In the early stages of Alzheimer's disease, short-term memory begins to decline when the cells in the hippocampus degenerate (see Figure 41). The ability to perform routine tasks also declines. As Alzheimer's disease spreads through the cerebral cortex, judgment declines, emotional outbursts may occur and language is impaired. Progression of the disease leads to the death of more nerve cells and subsequent behavior changes, such as wandering and agitation. The ability to recognize faces and to communicate is completely lost in the final stages. Patients lose bowel and bladder control, and eventually need constant care. This stage of complete dependency may last for years before the patient dies. The average length of time from diagnosis to death is 4 to 8 years, although it can take 20 years or more for the disease to run its course.
 

Figure 41 Alzheimer's Disease

•Transcendence - In this state, the subject experiences a feeling of merging the self with the rest of the universe. It used to be considered as the attainment of moving up to a higher level of existence. For example, in the ancient text of "Tao Te Ching" ("Book of Tao"), Lao Tsu (the author) mentioned that "Those who know do not talk. Those who talk do not know". A straight forward translation would mean someone is hiding knowledge from the prying eyes. A more subtle interpretation would attribute the silence as the difficulty to describe the experience by words. It has been known for some time that an area in the posterior partietal cortex (PPC) is responsible for the separation of self from the external environment. Impairment of this part of the brain would induce a feeling of union with the whole universe. A 2010 report in the Journal of Neuron confirm‎s this observation by checking on people with brain cancer. Those who have some neurons in the PPC removed, tend to believe in miracles, extrasensory perception and other non-material phenomena; while the others with intact PPC do not have such sentiments. It could be that Lao Tsu's claim about transcendental experience is real, but such occurrence can be explained in term of modern medical knowledge without invoking another level of existence. He must be able to inactivate the PPC somehow, perhaps via meditation.

•Vision - It is virtually impossible to carry out research into visions in the laboratory, because they do not happen on demand; as a result, the only evidence that visions do exist is the accounts of those people who have experienced them. Vision may occur in response to stress. They are often central to religious experience. Out-of-body experiences are not restricted to religious practices: they seem to occur in response to some kind of emergency situation. This is the case with near-death experiences.
 

There have been thousands of reports of near-death experiences, many noting the same types of sensations. Subjects feel as though they have left their bodies watching the scene unfold -- as if from above. Others saw deceased loved ones in a very peaceful and beautiful scene. Some people report traveling down a tunnel toward a bright light (Figure 43), where benevolent presences wait. Scientists have been unable to explain them conclusively. Some physiologists have suggested that hypoxia, or low oxygen levels in the brain, might cause a consistent pattern of hallucination in all sufferers. Other scientists argue that the experience stems from an acute bout of "REM intrusion" into the partially awakening state (in time of extreme stress) similar to narcolepsy - a neurological disorder characterized by uncontrollable bouts of sleep that can cause elaborate hallucinations and, sometimes, out-of-body experiences. The re-appearance of loved ones are explained as

the last of the dieing memory lingering on after the official declaration of death. Some neurologists suggest that tunnel vision is caused by lack of blood flow to the eye. The eye, the retina of the eye, is one of the most exquisitely sensitive tissues to a loss of blood flow. So when blood flow does not reach the eye, vision fails, and darkness ensues from the periphery to the center.
 

¶The challenge of finding an ideal model animal in which a physical basis of memory formation might be revealed was taken up in the 1960s by E. R. Kandel, who eventually received the Nobel Prize in Physiology or Medicine in 2000 for his efforts on investigating the nervous system with Aplysia. The Aplysia did not share the prize, but his daughter Minouche at the age of seven has written a poem to enshrine the animal:

An aplisa is like a squishy snail.
 In rain, in snow, in sleet, in hail.
 When it is angry, it shoots out ink.
 The ink is purple, it's not pink.
 An aplisa cannot live on land.
 It doesn't have feet so it can't stand.
 It has a very funny mouth.
 And in winter it goes to the south.