Sleep need during waking

Mathematical analyses of EEG SWA have yielded quantitative information about the time course of accumulation and discharge of sleep need. The dynamics of the sleep/wake-dependent changes in delta power have been quantified with the use of computer simulations, and delta power can now be predicted in detail. The increase of sleep need during waking can be described by an exponentially saturating curve with a time constant (Tj) of 18.2 hr in humans (37) and 8.6 hr in... 

The importance of adenosine deaminase in the duration and intensity of sleep in humans has been noted recently (Retey et al. 2005). Animal studies suggest that sleep needs are genetically controlled, and this also seems to apply in humans. Probably, a genetic variant of adenosine deaminase, which is associated with the reduced metabolism of adenosine to inosine, specifically enhances deep sleep and slow wave activity during sleep. Thus low activity of the catabolic enzyme for adenosine results in elevated adenosine, and deep sleep. In contrast, insomnia patients could have a distinct polymorphism of more active adenosine deaminase resulting in less adenosine accumulation, insomnia, and a low threshold for anxiety. This could also explain interindividual differences in anxiety symptoms after caffeine intake in healthy volunteers. This could affect the EEG during sleep and wakefulness in a non-state-specific manner. 

To understand this apparent paradox, we need to recognize that movement is programmed by the brain at many levels. The upper level of the brain, which gives us voluntary control over movement during waking, is pretty much out of the loop during sleep. The lower brain structures, many of which are necessary for movement,... 

Many animals hibernate during parts of the year, entering a state that is similar to a very deep sleep. But hibernation is more than simply a deep sleep. The animal s body temperature drops well below its normal range, the animal does not wake up for a long period of time, and its metabolism slows to the point that the animal does not need to eat or relieve itself during that period. 

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