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These are excerpts and elaborations from my book "The Nature of Consciousness"
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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 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). Back to the beginning of the chapter "Dreams" | Back to the index of all chapters |
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