- 2 decades agoFavorite Answer
Dreaming is the subjective experience of imaginary images, sounds/voices, words, thoughts or sensations during sleep, usually involuntarily. The scientific discipline of dream research is oneirology. Dreaming has been associated with rapid eye movement (REM) sleep, a lighter form of sleep that occurs during the latter portion of the sleep cycle, characterized by rapid horizontal eye movements, stimulation of the pons, increased respiratory and heart rate, and temporary paralysis of the body. (However, this association has been questioned since it may be that dream recall after REM sleep is common and because dreams are easier recalled after waking from the light REM sleep.) It also occurs in other phases of sleep, though dream recall is more difficult. Hypnogogia, which occurs spontaneously during the approach to deep sleep, is thought to be related to dreaming. Dreams are also associated with male erection about as frequently as with REM sleep.
Dreams are full of imagery. This imagery ranges from the normal to the surreal; in fact, dreams often provoke artistic and other forms of inspiration. Forms of dream include the frightening or upsetting nightmare and erotic dreams with sexual images and nocturnal emission.
Most scientists believe that dreams occur in all humans with about equal frequency per amount of sleep. Therefore, if individuals feel that they did not dream or that they only had one dream in any given night, it is because their memory of the dream has faded. This "memory erasure" aspect of the dream state is mostly found when a person naturally awakes via a smooth transition from REM sleep through delta sleep to the awake state. If a person is awoken directly from REM sleep (e.g. by an alarm clock), they are much more likely to remember the dream from that REM cycle (although it is most likely that not all dreams will be remembered because they occur in REM cycles, which are interrupted by periods of delta sleep which in turn have a tendency to cause the memory of previous dreams to fade).
For a long time true dreaming had only been positively confirmed in Humans, but recently there have been research reports supporting a view that dreaming occurs in other animals as well. Animals certainly undergo REM sleep, but their subjective experience is difficult to determine. The animal with the longest average periods of REM sleep is the armadillo. It would appear that mammals are the only, or at least most frequent, dreamers in nature, which is perhaps related to their sleep patterns. Many animals such as frogs probably do not sleep at all (except when in hibernaculum, which is a different kind of state). Some researchers have managed to deter the function of brain mechanism that locks body and limb movements during dreams. With this method it has been discovered that a cat seems to dream mostly about chasing a prey and playing with its prey.
Rapid eye movement (REM) is the stage of sleep during which the most vivid (though not all) dreams occur. During this stage, the eyes move rapidly, and the activity of the brain's neurons is quite similar to that during waking hours. It is the lightest form of sleep in that people awakened during REM usually feel alert and refreshed. The eye movements associated with REM are generated by the lateral geniculate nucleus and are associated with PGO (pons, geniculate, occipital) waves.
During a night of sleep, a person usually has about four or five periods of REM sleep, which are quite short at the beginning of the night and longer at the end. It is common to wake for a short time at the end of a REM phase. The total time of REM sleep per night is about 90-120 minutes.
Physiologically, certain neurons in the brain stem, known as REM sleep-on cells (located in the pontine tegmentum), are particularly active during REM sleep, and are probably responsible for its creation. The release of certain neurotransmitters, the monoamines (norepinephrine, serotonin and histamine) is completely shut down during REM. For this reason, the motor neurons are not stimulated by the brain's activity and the body's muscles don't move. The heart rate and breathing rate are irregular during REM sleep, again similar to the waking hours. Body temperature is not well regulated during REM, and it approaches the surroundings' temperature. Erections of the penis or clitoris are also common during REM. In fact, REM sleep is so physiologically different from the other phases of sleep that the others are collectively referred to as non-REM sleep.
The function of REM sleep is not understood; several theories have been advanced. According to one theory, memories are consolidated during REM sleep. However, the evidence seems scant; in people that have no REM sleep (because of brain damage) memory functions are not measurably affected. Another theory has it that the monoamine shutdown is required so that the monoamine receptors in the brain can recover to regain full sensitivity. Indeed, if REM sleep is repeatedly interrupted, the person will "make up" for it with longer REM sleep at the next opportunity. Interrupting REM sleep can improve certain types of depression, and depression appears to be related to an imbalance of certain neurotransmitters. According to a third theory, the REM sleep of newborns (often referred to as Active Sleep) provides the neural stimulation necessary to form mature neural connections; hence maturely born animals don't need much of it. Supporting this theory is the fact that the amount of REM sleep decreases with age.
REM sleep also occurs in other mammals. It appears that the amount of REM sleep per night in a species is closely correlated with the developmental stage of newborns. The platypus, whose newborns are completely helpless and undeveloped, has 8 hours of REM sleep per night; in the dolphin, whose newborns are almost completely functional at birth, there is almost no REM sleep.
The association between dreaming and REM sleep was discovered by Eugene Aserinsky and Nathaniel Kleitman in 1953.
- Anonymous2 decades ago