ABSTRACT
An approach combining time-continuous nonlinear stability analysis and a parametric bispectral method was introduced to better describe cortical activation and deactivation patterns in the immature fetal electroencephalogram (EEG). Signal models and data-driven investigations were performed to find optimal parameters of the nonlinear methods and to confirm the occurrence of nonlinear sections in the fetal EEG. The resulting measures were applied to the in utero electrocorticogram (ECoG) of fetal sheep at 0.7 gestation when organized sleep states were not developed and compared to previous results at 0.9 gestation. Cycling of the nonlinear stability of the fetal ECoG occurred already at this early gestational age, suggesting the presence of premature sleep states. This was accompanied by cycling of the time-variant biamplitude which reflected ECoG synchronization effects during premature sleep states associated with nonrapid eye movement sleep later in gestation. Thus, the combined nonlinear and time-variant approach was able to provide important insights into the properties of the immature fetal ECoG.
Subject(s)
Brain/embryology , Diagnosis, Computer-Assisted/methods , Electroencephalography/methods , Fetal Monitoring/methods , Sleep Stages/physiology , Animals , Brain/physiology , Female , Models, Theoretical , Nonlinear Dynamics , Pregnancy , Pregnancy, Animal , Reproducibility of Results , Sensitivity and Specificity , Sheep , Time FactorsABSTRACT
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.
