Measurement of fetal responses to vibroacoustic stimuli. Habituation in fetal sheep.

Electrocortical (ECoG) and integrated electromyographic (EMG) activity was recorded in 6 chronically prepared fetal sheep (132-145 days). Recording were made in fetuses prior to and during repeated vibroacoustic stimulation. In the undisturbed fetus, two patterns of ECoG activity were apparent; high (HV) and low voltage (LV). The fetus responded to this broad spectrum stimulus during both LV and HV ECoG activity. In 18 of the 20 experiments, repeated stimulation was not associated with a change in the background ECoG activity. All fetuses responded at least once to the stimulus. Habituation of the EMG response was observed during both HV and LV ECoG activity. The rate of habituation was independent of the background ECoG activity and was unchanged when experiments were repeated at intervals of more than 3 days. These results show that fetal sheep also respond to vibroacoustic stimulation and with repetition habituation occurs.