Sensitivity to auditory spectral width in the fetus and infant - an fMEG study

Auditory change detection is crucial for the development of the auditory system and a prerequisite for language development. In neonates, stimuli with broad spectral width like white noise (WN) elicit the highest response compared to pure tone and combined tone stimuli. In the current study we addressed for the first time the question how fetuses react to WN stimulation. Twenty-five fetuses (M-age = 34.59 weeks GA, SD +/- 2.35) and 28 healthy neonates and infants (M-age = 37.18 days, SD +/- 15.52) were tested with the first paradigm, wherein 500 Hz tones, 750 Hz tones, and WN segments were randomly presented and auditory evoked responses (AERs) were measured using fetal magnetoencephalography (fMEG). In the second paradigm, 12 fetuses (M-age = 25.7 weeks GA, SD +/- 2.4) and 6 healthy neonates (M-age = 23 days and SD +/- 6.2) were presented with two auditory odd-ball conditions: condition 1 consisted of attenuated WN as standard and 500 Hz tones and WN as deviants. In condition 2, standard 500 Hz tones were intermixed with WN and attenuated WN. AERs to volume change and change in spectral width were evaluated. In both paradigms, significantly higher AER amplitudes to WN than to pure tones replicated prior findings in neonates and infants. In fetuses, no significant differences were found between the auditory evoked response amplitudes of WN segments and pure tones (both paradigms). A trend toward significance was reached when comparing the auditory evoked response amplitudes elicited by attenuated WN with those elicited by WN (loudness change, second paradigm). As expected, we observed high sensibility to spectral width in new borns and infants. However, in the group of fetuses, no sensibility to spectral width was observed. This negative finding may be caused by different at tenuation levels of the maternal tissue for different frequency components.