Effects of hyperbilirubinemia on cerebrocortical electrical activity in newborns

In our study, cerebrocortical electrical activity was recorded as an indicator of bilirubin neurotoxicity. Bilirubin especially affects the thalamus and cerebral cortex. Inasmuch as rhythmic oscillations on the EEG arise from the interaction between cortex and thalamus, electrophysiologic effects of bilirubin on the rhythmic oscillations with long-term postnatal age were investigated. Brain maturation was also analyzed with power spectral analysis quantitatively. For this purpose, 141 EEG records were taken (in the first week, 15th d, at the end of the first month, and at the third month) from 17 infants with hyperbilirubinemia and 22 healthy infants. In all records, the major frequency component was formed by the delta frequency in both groups. In the first records of the hyperbilirubinemia group, the delta frequency was higher than the control group; however the theta, alpha, and beta frequencies and the amplitude levels were lower (p < 0.001). These changes were found to be significantly correlated with the bilirubin levels (p < 0.001). On the 15th d the amplitude of the hyperbilirubinemia group increased to similar levels as the control group. At the frequency bands of delta and theta, there were significant changes related to postnatal age (p < 0.001). In all cerebral regions, the delta frequency decreased and the theta frequency increased with age. However, in the hyperbilirubinemia group the delta frequency was higher, the theta frequency was lower, and the changes between the groups disappeared in the third month despite the differences at all regions of the brain. In terms of the vertex, k complex, and sleep spindle, there were no differences between both groups in the third month (p > 0.05). We conclude that hyperbilirubinemia affects the cerebrocortical electrical activity but appears to be time limited.