Individual differences in infants' sleep.

Individual differences in sleep patterns were repeatedly studied in 22 infants in a residential unit for mothers and babies at two, six, 12 and 20 weeks of age. Electroencephalogram, horizontal and vertical electro-oculogram, electromyogram of chin muscle, and respiration and body movements were recorded during the first two sleep cycles. The age factor was significant in all variables studied. The infants' individuality was significant in (1) the frequency of respiration during quiet sleep, (2) the frequency of rapid eye movement during paradoxical sleep, (3) the occurrence of regular EEG activity during paradoxical sleep, and (4) body movements during paradoxical sleep. Individual differences in these sleep variables persisted with considerable stability during the first five months of life.