Characterization of electroencephalographic state in fetal baboons

Long-term recordings of the electroencephalograms (EEGs) from the nonhuman fetal primate have been visually scored for state. Data were obtained from three fetuses using recently developed techniques for chronic instrumentation of the pregnant baboon. Seven days or more after surgery, nine chart records of 4-5 h in duration were analyzed. These records were made during an interval in gestation from 143 to 153 days (term = 175 to 185 days). Criteria for differentiation of EEG state were based on the presence (state 1) or absence (state 2) of trace alternant, which is the predominant characteristic of EEG activity during quiet sleep in human preterm and term infants. Two patterns of EEG activity were readily distinguished at both standard (30 mm/s) and compressed (30 mm/min) EEG chart speeds. On a minute-by-minute basis, there was an overall concurrence of 82.9% for EEG state when scored from compressed and standard EEG records. From the compressed records, state 1 was present on average 38.3% of the time, with a mean epoch duration of 15.1 min, while epochs of state 2 averaged 25.9 min. (DBO)