Nocturnal sleep in severely mentally retarded children: abnormal EEG patterns in sleep cycle.

Sleep EEG patterns in 43 mentally retarded children (from 4 months to 80 years of age) were studied throughout nocturnal sleep and the following results were obtained. (1) Twenty-two cases evidenced normal sleep patterns that could be classified into 6 stages. (2) The 21 other cases showed some abnormal sleep EEG patterns as follows: (a) absence of sleep spindles (n = 18) which included cases of high voltage fast activity (n = 2) and cases of low voltage activity throughout nocturnal sleep (n = 3); (b) indistinguishable delta and theta activities (n = 1), extreme spindle-like pattern (n = 1), absence of REM sleep (n = 1). (3) The severely mentally retarded children under 18 months had definitely decreased spindle activity in comparison to the values obtained by other authors from normal children. (4) The majority of the abnormal sleep EEG patterns occurred during light sleep. (5) A significant decrease in DQ was found in children with abnormal sleep patterns throughout NREM sleep as compared with those in whom abnormal EEGs occurred only during stages 1 and 2. (6) It was concluded that the EEG recorded in nocturnal sleep may serve as a useful indicator of abnormality in mentally retarded children.