Duration of spindle bursts during nocturnal sleep in mentally retarded children

Abstract

Sleep spindles longer or shorter than 0.4 sec in 90 mentally retarded children (from 6 months to 8 years of age) were studied throughout nocturnal stage 2 sleep. The 90 subjects were classified into 5 groups in terms of spindle length: group 1 subjects with the ratio (number of spindles longer than 0.4 sec/number of spindles shorter than 0.4 sec in duration) of more than 2.00; group 2 subjects with the ratio of 1.99-1.00; group 3 subjects with the ratio of 0.99-0.50; group 4 subjects with the ratio less than 0.50; group 5 subjects without any spindles. The following results were obtained. 1. (1) The subjects belonging to each group ranged anywhere from 6 months to 8 years of age. 2. (2) No significant difference was found among groups 1, 2, 3 and 4 in the number of spindles shorter than 0.4 sec. However, the spindles longer than 0.4 sec tended to be fewer in the order of groups 1 → 2 → 3 → 4. A significant decrease in the number of spindles longer than 0.4 sec was found in groups 2, 3 and 4 as compared with group 1, and in group 4 as compared with group 3. 3. (3) The abnormal clinical EEG tended to be more frequent in the order of groups 1 → 2 → 3 → 4 → 5. A significant increase in abnormal clinical EEG was found in group 5 as compared with group 1 and group 2, and in group 4 as compared with group 1. 4. (4) A significant decrease in DQ was found in groups 4 and 5 as compared with group 1, and in groups 4 and 5 as compared with group 2. 5. (5) It was concluded that the number of spindles longer than 0.4 sec may serve as a useful indicator of abnormality in mentally retarded children.