Development of the Sleep EEG in Normal Infants During the First Year of Life
Authors: Hagne Ingrid 
Published: January 2008

In order to aquire a comprehensive knowledge of the normal development of infant EEG, in particular its intra‐ and interindividual variations, a selected material of 29 full term healthy infants was studied longitudinally from birth to 1 year of age with EEG, neuropediatrie examinations and developmental tests. The program contained 2 examinations during the first 7 days, one at three weeks, and from 2 months an examination every second month. At follow‐up examinations at the age of 31/2–6 years all children were normally developed and without signs of neurological disease. The waking EEG:s have been described earlier. The present report gives an account of the neonatal records and the sleep records from the first year.

The essential features of the “typical” or “ideal” neonatal EEG are known from a rich literature. In the present paper special interest has been paid to EEG‐components which have been designated in earlier works as “deviations” or “variations” of uncertain significance, from the “ideal” EEG.

Paroxysmal activity was very frequent in the neonatal period. It appeared as typical, usually multifocal, sharp waves, but also in an atypical, rather blunt “sharp” wave form (the latter type of activity was designated as “questionably paroxysmal”). Bilaterally synchronous paroxysmal activity of diffuse distribution was infrequent. Paroxysmal activity was seen more often during sleep than in the waking state and more frequently in regular than in irregular sleep. The incidence of clearly paroxysmal activity amounted in the age group 4—7 days to 57.7%; if “questionably paroxysmal” records were included, the incidence rose to 69.2%. Only 4 of the 29 infants were consistently free from paroxysmal activity during their first 3 weeks of life. It is concluded, that paroxysmal activity of those types described in detail in the paper, must be regarded as a normal element in the neonatal EEG.

Considerable asymmetries of slow activity were seen in the episodes of “tracé alternant”, usually, however, with shifting side predominance from one episode to the other.

During the next few months the incidence of paroxysmal activity decreased rapidly and for the future such activity was present only occasionally. Towards the end of the first year, however, paroxysmal activity of an essentially new type appeared in a few records. In these cases diffuse and bilaterally synchronous bursts of high amplitude slow waves with spike components occurred.

Asymmetries of low frequency activity, usually in fronto‐temporal leads, were rather common. Only in two records was the asymmetry persistent throughout the sleep record. In 13 other records the side difference was transitory.

Sleep spindles displayed a considerable variability between individuals in respect to abundance, distribution over the cortex and synchrony between hemispheres.

The results obtained from this group of strictly normal infants, all of whom were re‐examined and found normal after several years, will facilitate a more reliable evaluation of EEG:s from infants suspect for cerebral abnormalities. Ultimately it will also be possible to evaluate the EEG of neonates and small infants as an instrument for diagnosis and prognosis of cerebral dysfunction.