When considering the different levels of wakefulness, by necessity we are confronted with the problem of sleep, a special state of unconsciousness that might be regarded as the negative reflection of orientation and attention. The alternation of sleep with wakefulness is the most characteristic example of the periodicity of vital functions. As will be seen in the following, a whole series of physiological problems have been solved in connection with the sleeping state. Nevertheless, a basic question is still unanswered: why do we have to spend one-third of our lives sleeping? By the time we reach the age of 60, we have slept 20 years, of which 15 years have been spent in deep dreamless sleep and 5 years dreaming vividly.
KeywordsSound Stimulus Paradoxical Sleep Deep Sleep Delta Activity Cerebral Area
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