The Nature of Consciousness

Piero Scaruffi

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These are excerpts and elaborations from my book "The Nature of Consciousness"

The Interpretation  of Dreaming

Much more important was a finding that remained neglected for almost a century: at the end of the 19th century the British neurologist John Hughlings Jackson (“On some implications of dissolution of the nervous system”, 1882) realized that a loss of a brain function almost always results in a gain in another brain function. Typically what is gained is heightened sensations and emotions. Jackson, virtually a contemporary of Darwin, explained this phenomenon with the view that the brain's functions have different evolutionary ages: newer ones took over older ones, but the older ones are still there, we just don't normally need to use them as the newer ones are more powerful. When we lose one of the newer features, then the older features of the brain regain their importance.  Jackson had the powerful intuition: that a single process was responsible for a "balance" of brain states.

One century later the Swiss pharmacologist Alexander Borbély derived a simple law of sleep  ("A two process model of sleep", 1982): the timing and intensity of sleep are due to the interaction between the sleep-independent circadian system (that dictates the 24-hour cycle) and a homeostatic mechanism (the less you sleep, the more you need to sleep, and viceversa). The latter expresses a fundamental need for balance between sleep and wakefulness.

An important discovery (probably the one that opened the doors of the neurobiology of dreams) was made by Eugene Aserinsky: dreaming is associated with a brain state of "rapid eye movement" (REM) that recurs regularly during sleep ("Regularly occurring periods of eye mobility and concomitant phenomena", 1953). His advisor, the Moldovan neurologist Nathaniel Kleitman and another student of his, William Dement ("Cyclic variations in EEG during sleep and their relation to eye movements, body motility, and dreaming", 1957), clarified that a brain enters REM sleep 4 or 5 times per night, at approximately 90-minute intervals, and each period lasts about 20 minutes.

In 1962 the French physiologist Michel Jouvet observed that REM sleep is generated in the pontine brain stem (or "pons").  In other words, Jouvet localized the trigger zone for REM sleep (and therefore dreaming) in the brain stem.

REM sleep exhibits four main properties:

·   A low level of brain activity

·   The inhibition of muscle tone

·   Waves of excitation from the pons

·   Rapid eye movement

The waves of excitation are probably the cause of everything else.  The pons sends signals and excites eye muscles (causing rapid eye movement), the midbrain (causing a low level of brain activity), and the thalamus. The thalamus contains structures for visual cognition, auditory cognition, tactile cognition and so forth. The thalamus then excites the cortex. The cortex therefore receives a valid sensory signal from the thalamus and interprets it as if it were coming from the eye, ears, etc.

During REM sleep several areas of the brain are working frantically, and some of them are performing exactly the same job they perform when the brain is awake.  The only major difference is that the stimuli they process are now coming from an internal source rather than from the outside world.

REM sleep is pervasive among mammals. Whatever its function is, it has to be the same for rats and humans.

The US neurophysiologist Allan Hobson and the US psychiatrist Robert McCarley argued that, far from being the center of production of dreams as Freud imagined, higher brain functions such as memory and emotion are simply responding to a barrage of stimuli that are generated from the brainstem ("The Brain as A Dream State Generator”, 1977). In other words, dreams originate from random brain activity (during REM sleep) which is then interpreted by the forebrain. The brain tries to make sense of what is going on, and what is going on is simply a continuous flow of random “thoughts”. Dreams have no meaning.

The US psychiatrist Scott Campbell and the Swiss biologist Irene Tobler provided the standard definition of sleep in four steps ("Animal sleep", 1984): 1. A reversible state during which voluntary movements do not occur; 2. Controlled by a circadian clock; 3. Accompanied by an increase in arousal threshold; 4. Controlled by a homeostatic system.

During the 2000s the US neurologist Clifford Saper identifiet the “sleep switch” in the hypothalamus (“A putative fip-flop switch for control of REM sleep”, 2006), and the Taiwanese neurologist Ying-Hui Fu discovered the gene that regulates sleep length in mammals  (“The Transcriptional Repressor DEC2 Regulates Sleep Length in Mammals”, 2009).


Sleep

Meanwhile, there was also progress in understanding sleep.

The US psychiatrist Scott Campbell and the Swiss biologist Irene Tobler provided the standard definition of sleep in four steps ("Animal sleep", 1984): 1. A reversible state during which voluntary movements do not occur; 2. Controlled by a circadian clock; 3. Accompanied by an increase in arousal threshold; 4. Controlled by a homeostatic system.

The Romanian neurophysiologist Mircea Steriade discovered the slow oscillations of NREM sleep (~0.5-1 Hz), due to groups of neurons that fire together for a relatively prolonged time (depolarization) and then fall silent for another prolonged time (hyperpolarization), and then resume their synchronized firing ("A novel slow oscillation of neocortical neurons in vivo", 1993).

During the 2000s the US neurologist Clifford Saper identifiet the "sleep switch" in the hypothalamus ("A putative fip-flop switch for control of REM sleep", 2006), and the Taiwanese neurologist Ying-Hui Fu discovered the gene that regulates sleep length in mammals ("The Transcriptional Repressor DEC2 Regulates Sleep Length in Mammals", 2009).


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