[Transitory EEG asymmetry at the start of quiet sleep in the newborn infant: 75 cases].

75 transient EEG asymmetries occurring during quiet sleep were studied. These asymmetries were obtained from 73 polygraphic recordings registered in 73 neonates. These infants represented 3.17% of all the neonates registered during the neonatal period in a department of neonatology (2297 neonates registered between July 1974 and July 1982). The pattern of these asymmetries was always identical, it consisted of a sudden flattening of the EEG activity occurring on one hemisphere followed on this hemisphere by an EEG activity which was more discontinuous and less mature than on the other hemisphere. These asymmetries were transient, lasting from 1 to 5 min. They occurred at the beginning of quiet sleep. The EEG activity before and after the asymmetry was almost always normal. The analysis of the clinical data showed that the infants who presented an EEG asymmetry during quiet sleep had a conceptional age ranging from 35 to 44 weeks, and that they were hospitalized for a minor illness which turned out to be a neurological disorder in only 2 cases. It showed that all the infants who were followed later, except one, developed normally. The physiological mechanism of these asymmetries is discussed and it is concluded that they are functional, probably enhanced by a sleep deprivation and not associated with a focal pathology.