Dreaming is the subjective experience of imaginary images, sounds/voices, thoughts or sensations during sleep, usually involuntarily. Dreaming is associated with rapid eye movement (REM) sleep, a lighter form of sleep that occurs during the later 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. It can also occur in other phases of sleep, though this is less common. Hypnogogia, which occurs spontaneously during the approach to deep sleep, is thought to be related to dreaming.
Dream 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), he will much more likely remember his dream from that REM cycle (although it's 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.)
True dreaming has only been positively confirmed in homo sapiens, but many believe 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.
09-27-2008, 09:57 PM
