DELTA (0.5-1.5 HZ) AND SIGMA (11.5-15.5 HZ) EEG POWER DYNAMICS THROUGHOUT QUIET SLEEP IN INFANTS

Twenty-eight healthy infants, split into 3 groups according to age (gr oup 1: 2-6 weeks, n = 10; group 2: 7-14 weeks, n = 10; and group 3: 4- 12 months, n = 8), were recorded during the whole night. For each infa nt, the longest quiet sleep (QS) phase occurring between 8 p.m. and mi dnight was selected for EEG power spectral analysis. The power in the frequency band related to low-frequency delta waves (0.5-1.5 Hz, ''del ta band'') and the power in the frequency band related to sigma spindl es (11.5-15.5 Hz, ''sigma band'') were analyzed. Group 1 infants showe d no significant modification of the power in the sigma band in the co urse of the QS phase; the power in the delta band showed a significant increase between the second and the third 5 min segment and a decreas e thereafter. Group 2 infants showed a progressive reduction of the po wer in the sigma band, whereas the power in the delta band increased d uring the first 15 min. In group 3 infants, the sigma band power signi ficantly decreased between the third and the fifth 5 min segment witho ut further changes. The power in the delta band, on the contrary, incr eased progressively for the first 20 min and showed a second progressi ve increase beyond 35 min. For both group 2 and group 3 infants, it ap peared that the change in delta power preceded the change in sigma pow er. The above results provide quantitative evidence that a well-define d temporal inhomogeneity pattern in the EEG of the QS phase may appear between 7 and 14 weeks of age and continues from the fourth month on.