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Biology 202
2003 First Web Paper
On Serendip

The Neurophysiology of Sleep and Dreams

Alexandra Lippman

The ancient Babylonians thought dreams were messages from supernatural beings, and that the good dreams came from gods and that bad dreams came from demons. (1) Since then people have sought many different explanations for the occurrence and importance of dreams. Before beginning to understand the function or significance of sleep and dreams, it is important to look at when, what, where, and how dreaming and sleeping occur.

Adult humans sleep, or should sleep, for about eight hours a day. People's necessary time spent sleeping changes over time. Newborns spend about twice as long sleeping. (2) Circadian rhythms, [the term originates from the Latin, "circa diem," which means about "about a day" (3)] determine when people fall asleep. The circadian rhythm, actually twenty-five hours long, is reset by light. (4) In 1953 scientists discovered REM (rapid-eye movement) sleep. The physiological state of REM occurs periodically with NREM (non-rapid-eye movement) about every ninety minutes (5), and lasts for about 20-30 minutes (6).

Differences between NREM and REM can be measured using an electroencephalogram (EEG), electrooptogram (EOG), and electromyelogram (EMG), which measure brainwaves, eye-movement, and muscle tone, respectively. REM is categorized by high-frequency, low-amplitude, more irregular waves in EEG, rapid, coordinated movement in EOG, and weak EMG. During this type of sleep, brain activation heightens, breathing and heart rates increase, and body movement is paralyzed. Because the person is highly aroused, like in waking, but also very asleep, REM sleep is also called paradoxical sleep (6).

Although dreams and REM are not synonymous, most dreaming occurs during REM sleep. Dreaming during the REM sleep can be seen as a "state of delerium possessing qualities of hallucination, disorientation, confabulation, and amnesia." (7) While as many as 70-95% of people awakened during REM remember their dreams, only 5-10% of those awakened during NREM report dreams (5).

The release of different neurotransmitters in different areas seems to determine which type of sleep should be activated. At the onset of sleep serotonin is secreted and seems to trigger NREM. (4) NREM switches to REM sleep with the release of the chemical, acetylcholine, in the pons, which is located in the base of the brain, and later the re-release of noradrenaline and serotonin seems to switch off REM (5) (7) and reactivate NREM sleep again. The action of the neurotransmitters as triggers of NREM and REM sleep is referred to as the reciprocal interaction/activation synthesis. (5) With the excretion of acetylcholine, signals from the pons are sent to the thalamus, which relays them to the cortex, and also sent to shut off the neurons in the spinal cord, which causes the temporary paralysis of the body.

Although the pons is responsible for REM sleep, dreams originate in areas in both the frontal lobe and also at the back of the brain. In twenty-six cases in neurological literature about damage to the pons, although there was a loss of REM sleep in all of them, loss of dreaming was reported in only one of the cases. (5) Also while damage to frontal areas of the cortex makes dreaming impossible, the REM cycle of the individual, whose brain is damaged that way, remains unaffected. (5)

Because most dreaming does occur during REM sleep, however, the REM state can be thought of as one of the triggers for dreaming. (5) The pons' paralyzing of the muscles is an important precondition for dreaming, since without that paralysis dreamers might act out their dreams (the effects of this problem can be seen in individuals suffering from REM Behavior Disorder). Thus, without muscle atonia, dreaming could be a very dangerous activity!

Understanding the nature of the areas of the cortex that are responsible for dreaming may help explain the reasons behind the content of dreams. The area of the frontal lobes, which is responsible for dreaming, contains the "large fiber pathway, which transmits the neurotransmitter dopamine from the middle part of the brain to the higher parts of the brain. " (5) The use of dopamine stimulants, such as L-dopa, massively increases the intensity and frequency of dreams. (5) Since the frontal and limbic areas of the brain are concerned with arousal, emotion, memory, and motivation (5), dreaming might be tied to these aspects of behavior based on its location in the brain. The gray cortex at the back of the brain, also responsible for dreaming, is connected to abstract thinking and is where the highest level of perceptual information is processed. (5) The activation of this location seems to be related to the huge importance of visual perception in dreams.

Although the functions of REM sleep and dreams is not fully agreed upon or understood, evidence for the necessity of sleep is incontrovertible. Rats deprived of sleep die after a few days. Also REM sleep and dreaming seem to be quite important since the individual deprived of REM sleep, will respond with REM rebound, which means that the amount of time spent in the REM state will increase following REM deprivation. (6) Also the attempts at entering REM increase, and individuals show more anxiety and irritability, and have trouble concentrating during the day. (8) Animals deprived of REM also show an increase in attempts at entering REM, and display other behavioral disturbances, such as increased aggression. (8) Thus, while in a future web-paper I intend to discuss and investigate more the functions of NREM and REM sleep, a knowledge of the processes at hand seemed necessary before such a discussion to occur.

References

1)The Association for the Study of Dreams
2)Harvard Undergraduate Society for Neuroscience
3)Silent Partners Organization
4)Talk About Sleep
5)The American Psychoanalytic Association
6)California State University student essay
7)"Neurophysiology of dreams"
8)Slides on Physiology of Sleep and Dreaming


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