Time-Variant Analysis of Nonlinear Stability and Bispectral Measures to Quantify the Development of Fetal Sleep States

A combined time-variant analysis of nonlinear stability and parametric bispectral measures was applied to the in utero electrocorticogram (ECoG) of fetal sheep between 0.7 and 0.9 gestation to examine the maturation of sleep states and synchronization patterns of the ECoG. Cycling of the nonlinear stability of the fetal ECoG occurred already at 0.7 gestation and suggests the presence of premature sleep states. This was accompanied by cycling of the time-variant biamplitude which reflected ECoG synchronization effects during premature NREM sleep. Maturation of NREM sleep begun at 0.78 gestation and preceded that of REM sleep that begun at 0.85 gestation. Our results suggest that maturation of brain stem and thalamic function precedes that of cortical function