Maturation of Auditory Steady-State Responses in Normal Babies

Abstract

In Brief Objective: To track the development of the auditory steady-state response (ASSR) through the neonatal and early infant periods in a group of normal-hearing babies. Design: This longitudinal study involved assessment at four data collection points. ASSR thresholds to modulated 500 Hz and 4 kHz tones were established in 20 full-term subjects at 0, 2, 4, and 6 wks of age. Results: Significant developmental changes were observed for both test frequencies. Mean ASSR threshold levels decreased by approximately 10 dB between the week 0 and week 6 data collection points. Conclusions: The results of this study indicate that ASSR threshold levels in normal-hearing neonates and young infants are different from those observed in older subjects. Clinical application of the ASSR procedure in this population will need to take into account developmental changes occurring in the first weeks of life. Furthermore, the findings indicate that ASSR thresholds in normal-hearing babies at 6 wks of age are not yet mature. The advent of neonatal hearing screening has meant that babies are now routinely referred for diagnostic auditory evoked potential assessments in the first few weeks of life. Auditory steady-state response (ASSR) testing is one technique that has been proposed for frequency specific assessment of hearing in this popula-tion. However, the maturational course of the ASSR in neonates is unclear. This longitudinal study tracks the development of response threshold levels for a group of normal babies in the first 6 weeks of life. Sig-nificant maturational effects were observed with mean thresholds decreasing by approximately 10 dB across the recording period. As such, it appears that clinical application of the ASSR technique in the neonatal and early infant periods will need to take into account developmental changes.