Vibroacoustic Stimulation with a Complex Signal: Effect on Behavioral State in Fetal Sheep

Abstract

An ideal vibroacoustic stimulus for testing fetal reactivity has yet to be developed. In the present study in fetal sheep we tested the effect on behavioral state of an amplitude and frequency-modulated signal produced at the abdominal surface of the ewe. The stimulus was presented during periods of fetal non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. Evaluation of behavioral state was accomplished by visual observation of strip-chart recordings. Assessed in this manner, vibroacoustic stimulation during NREM sleep consistently resulted in a change to an indeterminate state. However, stimulation during 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 in a decrease in total power from 100 to 35 ± 4% (p < 0.05). Stimulation during REM 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 frequency, implying central arousal.

Effects of Impulse Noise Stimulation on Electrocorticogram and Heart Rate

“…4, early delta-band reduction) indicated that brainstem-thalamocortical connections were well developed in near-term fetal sheep. The timing of the changes in the frequency content of the ECoG that occur after impulse stimulation as well as the direction of amplitude changes as presented in table 1 agree with those of previous studies [9,10].…”

“…Table 1. Summary of the results from the current study (impulse stimulation) compared to previous studies using an electronic artificial larynx (EAL) [9] and vibroacoustic stimulation (VAS) [10] Current study Bauer et al [9] Abrams et al [10] impulse…”

“…Apart from these generalized motor responses, the specific and subtle effects of impulse sounds on fetal behavioral state have not been clearly elucidated. The pregnant ewe was felt to be a good animal model because of its extensive use in the past for evaluation of the effects of continuous sound on FHR ECoG and EOG [10], transmission properties of speech [17] and music [18], and increased glucose utilization along the central auditory pathway in fetal sheep [19].…”

“…Steady-state vibroacoustic stimulation, produced by a mechanically vibrating sound source applied directly to the abdomen induced changes in the behavioral state of human [8] and sheep fetuses [9,10]. The sheep as an animal model for human fetal response to sound stimulation has been used recently because sheep fetuses hear before birth [11], as do human fetuses [12,13], and because of dimensional and, therefore, sound transmission similarities of the abdomen [4,14].…”

“…Steady-state vibroacoustic stimulation applied to the abdomen of pregnant sheep, while the fetus is in either rapid eye movement (REM) or non-rapid eye movement (NREM) sleep, induced marked changes in fetal electrocortical activity [9,10]. Whether or not impulse noise evokes similar responses in fetal sheep has not been determined.…”