DC-EEG discloses prominent, very slow activity patterns during sleep in preterm infants

Objectives: The objective of this study is to test the hypothesis that the immature human brain exhibits slow electrical activity that is not detected by conventional (i.e. high-pass filtered) electroencephalography (EEG). Methods: Six healthy preterm infants (conceptional age 33–37 weeks) were recorded bedside with direct current (DC) EEG during sleep. Epochs with quiet sleep were selected to study the delta frequency bursts during discontinuous EEG patterns (trace discontinu or trace alternant), and we compared the waveforms obtained without filtering (i.e. genuine DC-EEG) to those seen after high pass filtering of the same traces. Results: In all infants, DC-EEG demonstrated that the typical delta frequency bursts are consistently embedded in very large amplitude (200–700 μV) and long lasting (1–5 s) occipitally negative transients, which are not seen in conventional EEG. Conclusions and significance: Our study demonstrates that (i) the most prominent spontaneous EEG activity of a sleeping preterm infant consists of very slow, large amplitude transients, and (ii) the most salient features of these transients are not seen in conventional EEG. Proper recording of this type of brain activity by DC-EEG provides a novel way for non-invasive assessment of neonatal brain function.