Investigation of nonlinear ECoG changes during spontaneous sleep state changes and cortical arousal in fetal sheep

We examined the precesses of cortical activation and deactivation of the fe tal brain during spontaneous sleep state transitions and during central ner vous processing of vibroacoustic stimulations (VASs) using nonlinear analys is of the electrocorticogram (ECoG). Tests of nonlinearity and a random shu ffling routine revealed deterministic and nonlinear portions in the fetal E CoG. As common nonlinear measures are not applicable to nonstationary time series, we developed an algorithm to estimate the predictability of the ECo G in its time course by means of a point prediction error (PPE). The ECoG w as recorded before and during VAS from the maternal abdominal surface in se ven chronically instrumented fetal sheep at 0.8 of gestation. The PPE durin g REM sleep was significantly higher than during NREM steep. VAS in NREM sl eep resulted in an abrupt increase of the PPE not reaching the level of REM sleep. The steep increase of the PPE at onset and its slow decrease after cessation of the stimulus were very similar to the dynamics of spontaneous sleep state transitions, suggesting the involvement of the same cortical ac tivating mechanisms. In conclusion, the stage and the time course of fetal brain activation and deactivation patterns can be clearly shown by PPE tech niques. The PPE is a useful complement to spectral analysis. Both technique s describe different properties of the ECoG.