VIBROACOUSTIC STIMULATION WITH A COMPLEX SIGNAL - EFFECT ON BEHAVIORAL STATE IN FETAL SHEEP

An ideal vibroacoustic stimulus for testing fetal reactivity has yet t o be developed. In the present study in fetal sheep we tested the effe ct on behavioral state of an amplitude and frequency-modulated signal produced at the abdominal surface of the ewe. The stimulus was present ed during periods of fetal non-rapid eye movement (NREM) sleep and rap id eye movement (REM) sleep. Evaluation of behavioral state was accomp lished by visual observation of strip-chart recordings. Assessed in th is manner, vibroacoustic stimulation during NREM sleep consistently re sulted in a change to an indeterminate state. However, stimulation dur ing REM sleep failed to have an effect. Additional evaluation applying spectral analysis to the fetal electrocorticogram during stimulation in NREM sleep revealed a marked decrease in delta band power from 100 to 27 +/- 5% and in theta band power from 100 to 40 +/- 4% resulting i n a decrease in total power from 100 to 35 +/- 4% (p < 0.05). Stimulat ion during REM Behavioral state sleep revealed a significant increase in beta band power from 100 to 123 +/- 14%. Vibroacoustic stimulation in both NREM and REM sleep led to an increase in spectral edge frequen cy, implying central arousal.