Vexen's Guide to the Biology of Dreaming
Page by Vexen Crabtree, 2005 Mar 20
Dreams are memories of our semi-conscious thoughts and experiences that occur when we are asleep. As far as we know all mammals dream and some animals (but not Humans) can die from lack of it1. Us Humans spend on average, five to ten hours asleep per day, and one twelth of our lives dreaming, whilst reptiles and other lower organisms do not dream2. Dreams occur because our brain is very sensitive to input and stimulation, and even as we sleep our neurones are firing. Our brain continues to interpret these 'random' inputs, often taking into consideration things that have been occurring recently in the persons' life, or things that the person, consciously or unconsciously, has brought to the forefront of their mind.
Why do we need to sleep?
Horne, J4
People have put forward different reasons as to why we need to sleep. "Psychological theories are usually of a psychodynamic type, such as Jung's and Freud's, or of an information processing type, such as Calvin Hall's cognitive theory or Evan's computer theory"3. Psychodynamic theories are those that place most importance on the processing of unconscious thoughts, and more biological-mechanical theories place more importance on the ordering of all thoughts and memory.
The Processes of Sleep
Brain Waves:
“On an ongoing basis - even during sleep - electrical signals are constantly flashing over the brain; these signals can be detected and measured by an encephalograph. [...] These devices show that electrical signals in the brain don't come steadily, but are produced in short bursts like a series of waves; the shape of the waves change with the activity level of the brain.Brain waves are measured in up to 30 cycles per second. [...] During wakefulness, the waves are fast and small (called Alpha Waves); intense thoughts or walking around will produce faster, sharper, more-jagged rhythms characteristic of beta waves. In deep sleep, the brain produces large, slow delta waves, and theta waves are seen in babies and during sleep.”
"The Brain Encyclopedia" by Carol Turkington
REM Sleep
Whilst falling into deep sleep, our brain goes through a series of stages. These stages cycle throughout the night, differing according to our different sleeping patterns and internal states. Different patterns of waves, as measured on ECGs, characterize different stages of sleep.
“About 80 minutes after you fall into slumber, your activity cycle will increase slightly. The delta waves will disappear, to be replaced b the beta waves that signal an active or "awake" brain. Your eyes will begin to dart around under your closed eyelids as if you were looking at something occurring in front of you. This period of Rapid Eye Movements is called REM sleep. During the first sleep cycle, REM sleep usually lasts from 8 to 15 minutes. In subsequent cycles, REM sleep may last for 40 minutes or more. Overall, you spend from 15 to 35 percent of the night in REM sleep.”"Understanding Human Behavior" by McConnel, James V
Our eyes go through bursts of movement during REM sleep, sometimes with a few minutes in between bursts. During a full undisturbed nights sleep four or five periods of REM sleep is normal, each one being longer than the one before.
Sexual Arousal
During REM sleep, "most males experience an erection of the penis, and most females experience vaginal swelling and sometimes a hardening of their nipples. This sexual arousal typically occurs at the onset of each Stage 1-REM sleep period"[McConnel].
Muscle Inhibition
During REM our muscles are inhibited from moving although our brains still send impulses to them, but during other phases of sleep we're not disabled. Sleepwalking, therefore, occurs during Stage 4 deep sleep, a time when we have none of the beta waves that indicate reactive brain activity.
The Biology of Dreaming
"Dreams, in one form or another, tend to occur throughout the sleep period. [...] Generally speaking, most organized and detailed dreams occur during REM sleep"[McConnel].
The cortex is the most recent part of our brains to evolve, and is generally said to be responsible for our 'higher functions'. The interaction between our limbic system and the cortex is responsible for our conscious experiences of emotions and sensations. The cortex is 'highly active' during REM sleep, despite the fact that most external stimulation is cut off. According to the activation-synthesis model dreams are a result of our cortex/mind interpreting the 'random' and unregulated processes of sleep as if they were real events:
“Not only is the cortex isolated (unable to control muscles) but there is also inhibition of incoming signals produced by the sensory systems (so perceptions of the 'real' world are selectively attenuated) (input blockade). Hindbrain and midbrain structures, normally involved in relaying sensory information to the cortex, spontaneously generate signals (PGO waves) responsible for cortical activation and are also indistinguishable from signals which would normally have been relayed from the eyes/ears. [...] So the brain is very active during REM and dreams are a conscious interpretation (synthesis) of all this activity. The cognitive system, which organizes sensory information into the simplest meaningful interpretation when we are awake, processes all the internally generated signals as if they came from the outside world. In combination with oculomotor activity, PGO waves are sent to the visual and association cortex and the thalamus. [...].”
"Psychology: The Science of Mind and Behaviour" by Richard Gross, p86
The activation-synthesis model of dream interpretation holds that the basically random source of electronic information causes the activation of specific areas of the cortex. This randomness underpins the resulting synthesis that our cortex tries to make of it.
“Allan Hobson and Robert McCarley of Harvard University propose an "activation-synthesis" hypothesis, which explicitly rejects the Freudian, psychological interpretations. Instead, dreams, or at least some of their bizarre features, are seen as the associations and memories of the cerebral cortex that are elicited by the random discharges of the pons during REM sleep. Thus the pontine neurons, via the thalamus, activate various areas of the cerebral cortex, elicit well-known images or emotions, and the cortex then tries to synthesize the disparate images into a sensible whole. Not surprisingly, the "synthesized" dream product may be quite bizarre and even nonsensical because it is triggered by the semirandom activity of the pons.”"Neuroscience" by Bear, Connors and Paradiso, p470-471
Lucid Dreaming
“According to Stanford psychologist Stephen P. La Berge, lucid dreaming is most likely to occur during the last dream cycles of the night. La Berge states that, during a lucid dream, you are aware that your "experiences" are dreams rather than reality, and you can remember the dream quite well after you have wakened. Sometimes you can even evaluate what is happening during the dream, and take an active role in resolving the conflict that occurs.”"Understanding Human Behavior" by James V. McConnel, p66
"Delusional Fear": A partially lucid dream from 2004 is an example: I realized I was 'in' a dream, and with that realisation I was able to modify what was happening in the dream (and break the laws of physics).
Page by Vexen Crabtree, 2005 Mar 20
References: (What's this?)
Bear, Connors and Paradiso
"Neuroscience" (1996). Published by Williams & Wilkins, Baltimore, Maryland, USA. The Amazon link is to a newer version. Mark F. B ear Ph.D. and Barry W Connors Ph.D. both Professors of Neuroscience at Brown University, Rhode Island, USA, and Michael A. Paradiso Ph.D., associate professor.
Gooch, Stan
"Creatures from Inner Space" (1984 hardback). Published by Rider & Company, London, UK. [Search Amazon.co.uk. [Book Review]
Gregory, Richard L.
"The Oxford Companion to the Mind" (1987). Oxford University Press, Oxford, UK. Quotes from 1987 reprint.
Griffin, Joseph
"The Origin of Dreams" (1997 hardback).
Gross, Richard
"Psychology: The Science of Mind and Behaviour" (1996 3rd ed). Published by Hodder & Stoughton, London UK.
McConnel, James V.
"Understanding Human Behavior" (1986 hardback 5th ed). Originally published 1974. CBS College Publishing, Holt Rinehart and Winston, New York, USA.
Turkington, Carol
"The Brain Encyclopedia" (1996). From 1999 paperback edition published by Checkmark Books, USA.