There is currently broad interest in the effects of sound on the human fetus, but very little published quantitative information on the nature of the fetal acoustic environment and the central nervous system's response to specific sound stimuli. The long-term objectives of the present application are to provide answers to two questions. First, what are the characteristics of the sound environment of the fetus in utero? Preliminary research has shown that the fetal environment is rich with external sounds, that low (less than 0.25 kHz) frequencies are enhanced by up to 5 dB, and that high (greater than 2 kHz) frequencies are attenuated by up to 20 dB. We now propose to map the sound levels to various parts of the amniotic fluid and develop a mathematical model to describe the non-uniformity of intrauterine sound transmission loss. Measurements of the sound transmission loss in pregnant women at the level of the cervix are planned. For these experiments, an electronic artificial larynx, a vibroacoustic device currently use as a adjunct in the fetal non-stress test, will be employed. The second question to be answered is, What are the effects of transmitted sound on centra auditory structures of the fetus? It is proposed in this application to asses sound-induced neuronal activity in the fetal brain by resultant changes in local cerebral glucose utilization, using (14C)deoxyglucose as a tracer. Cerebral blood flow along the auditory pathway, which is anticipated to increase during enhanced functional activity, will be measured by the iodo(14C)antipyrine method, with the vascular time course being assessed by a heated thermocouple technique. Finally, the fetal auditory brainstem response will be recorded will surface electrodes in response to signals delivered through speakers external to the mother. The fetus will be delivered and brainstem responses will be recorded with the same stimuli.
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