Effect of Prenatal Sound Stimulation on the Morphology of Auditory Thalamic Relay Nuclei of Domestic Chick

Background: The knowledge of the effects of prenatal sensory environment on the development of sensory systems and other behavioral traits has important implications with regard to the optimum management of preterm infants. There is a controversy regarding the potential benefits and hazards of providing supplemental sensory stimulation to preterm infants. The views range from the perceived importance of minimal handling and reduced stimulation of preterm infants on one end, to the value of providing supplemental tactile, vestibular, auditory or visual stimulation (either alone or in combination) in promoting normal development at the other end. It is therefore important to know whether early prenatal stimulation of one sensory modality can affect behavioral responsiveness to stimulation of another different sensory system. Aims & Objective: The present study is aimed to see the effects of prenatal sound stimulation on the auditory thalamic nuclei in the domestic chick by examining quantitatively some morphological parameters. Materials and Methods: The auditory stimulus of frequency ranging between 100-6300 Hz at 65 dB was given to the chick embryos from E10 to E20. One group was given species-specific sounds of maternal calls (100-1600 Hz) from E10-E15 followed by chick hatchling calls (1600-6300 Hz) from E15-E20. The other experimental group received sitar music sounds given as slow music (1001600 Hz) from E10-E15 followed by fast music (100-4000 HZ) from E15-E20. The volume, neuronal number and neuronal nuclear area of nucleus ovoidalis, and nucleus rubera motor nucleus were quantitatively evaluated on serial Nissl stained sections by stereological methods. Results: Following the auditory stimulation, the nucleus ovoidalis, which is an important auditory nucleus, shows a considerable increase in volume and neuronal number. In concurrence with the effects on other brainstem auditory nuclei studied earlier, the prenatal auditory stimulation also has a positive influence on the developing auditory thalamic nucleus ovoidalis. The nucleus ruber showed no change in volume and neuronal nuclear area but only some increase in the neuronal number. Conclusion: The study demonstrates the positive effect of stimulation of one sensory modality (sound) on development of auditory system.