The ontogeny of fetal lamb electrocortical activity: a power spectral analysis.

With the use of a relatively inexpensive microcomputer-based system for power spectral analysis, we have been able to provide quantitative information on maturational changes in electrocorticogram waveforms in the third-trimester fetal lamb. Twenty-six electrocorticogram recordings were obtained from nine fetal lambs, with gestational ages ranging from 114 to 139 days' gestation. The transition from disorganized to cyclic electrocorticogram activity (high-voltage slow activity and low-voltage fast activity) occurred at approximately 115 to 120 days' gestation. However, quantitative changes in waveform characteristics of the electrocorticogram continued throughout the rest of gestation. These maturational changes occurred primarily in the low-voltage fast activity periods, with a decrease in power density in the delta (0.3 to 3 Hz) band and an increase in the maximum frequencies detected in the beta (15 to 30 Hz) band. There were no significant changes in the power spectrum of the high-voltage slow activity periods as a function of gestational age.