The first phase of nocturnal sleep in mentally retarded children.

The first phase of sleep observed in 104 mentally retarded children (from 3 months to 8 years of age) was studied throughout nocturnal sleep, and the following results were obtained. In 4 out of 104 subjects, REM sleep onset was observed, and in the remaining 100 subjects NREM sleep onset was found at the first wakefulness-sleep transition of the night. Following awakenings (lasting 4 min or more) during the night, 170 (51.7%) out of a total of 329 samples were REM sleep onset, and 159 (48.3%) showed NREM sleep onset. The phases of sleep onset and those following awakenings evidenced no correlation between the frequency of NREM sleep onset and DQ or clinical EEG, whereas a positive correlation was found between the frequency of NREM sleep onset and age.