Non-linear changes of electrocortical activity after antenatal betamethasone treatment in fetal sheep

1. We determined the effects of betamethasone on the fetal sheep electrocor ticogram (ECoG) using linear (power spectral) and non-linear analysis. For non-linear analysis we used an algorithm based on the Wolf algorithm for th e estimation of the leading Lyapunov exponent which calculates a,prediction error based on the course of the time series in the phase space. A high pr ediction error stands for low predictibility or low regularity and vice ver sa. 2. After 48 h of baseline recordings, vehicle (n = 6) or betamethasone (n = 7) at 10 mug h(-1) was infused over 48 h to the sheep fetus at 128 days ge stational age (0.87 of gestation). 3. ECoG spectral analysis revealed no difference in power spectrum between vehicle- and betamethasone-treated fetuses. The prediction error of the ECo G during REM sleep was higher than during non-REM or quiet sleep in both gr oups (P < 0.0001) revealing lower causality of brain activity during REM sl eep. During REM sleep, prediction error significantly decreased 18-24 h aft er onset of betamethasone treatment (P < 0.05) and returned to baseline val ues within the following 24 h of continued betamethasone treatment. No ECoG changes were found during quiet sleep. Non-linear ECoG changes during meta bolically active REM sleep accompanied the previously described decrease in cerebral blood flow. 4. These results suggest that betamethasone in doses used in perinatal medi cine acutely alters complex neuronal activity.