Jenkins & Dallenbach (1924) could show for the first time that learning tasks which are presented before sleep could be keep better than tasks that are presented before wakefulness. This was confirmed in other studies (Hennevin et al. 1995, Smith 1996). The discovery of REM sleep (Dement & Kleitman 1957) was the start for a more specific research program in which certain stages of sleep each were assigned specific roles for the memory processes. As follow on one hand, REM sleep, was attributed partly memory-favouring effects because of its particular physiological changes, on the other hand, as well as the Slow Wave Sleep (SWS) was attributed the same effects (Hobson & McCarley 1977, Crick 1983, Wilson & McNaughton, 1994, Karni et al. 1994, Squire & Alvarez 1995).
One of the studies on cognitive deficits in the thinking, memory, communication and the ability to learn new information in OSAS patients comes from Kales (1985). In this study 76% of OSAS patients show cognitive deficits in all these areas. A study by Naegelé et al. (1995) showed that the executive functions, which are important for the acquisition of information during memory processing in OSAS patients, were impaired. It is assumed that in sleep disorders the often found reduced sleep quality leads, as a result of Slow Wave Sleep or REM suppression, increased nocturnal arousal responses or prolonged awakenings to a reduced recovery function of night sleep (Weeß et al. 1998a/b). According to Jennum et al. (1993), Insomnia and sleepiness affect cognitive functions. Patients with excessive daytime sleepiness complaints have special problems in situations of physical relaxation and during long monotonous concentration tasks (Schwarzenberger-Kesper et al. 1987).
Cassel et al. (1989) were able to detect in Sleep Apnea patients a reduced cognitive performance and a decreased non-verbal processing speed. In this connection they were able to detect a reduced cognitive processing speed on ZVT in OSAS patients. Also Kotterba et al. (1997) detect in 32 of 40 OSAS patients abnormal results on the ZVT. In another study of Kotterba et al. (1998), they found in OSAS patients an impairment of the central nervous system activation (alertness), of the selective attention and of the sustained attention. Barbé et al. (1998) verified in Sleep Apnea patients a decreased vigilance.
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