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Middle latency auditory evoked responses in normal term infants: a longitudinal study
S H Rogers1, D A Edwards, D J Henderson-Smart
1Dept. of Perinatal Medicine, King George V Hospital, Sydney, Australia.
Insights
This study tracked middle latency auditory evoked responses (MLAERs) in infants from birth to one year. Auditory brainstem development shows significant changes in MLAERs, reaching adult-like patterns by seven months.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Auditory Neuroscience
Background:
- Middle latency auditory evoked responses (MLAERs) are crucial for assessing auditory pathway development.
- Understanding MLAER maturation provides insights into early auditory processing in infants.
Purpose of the Study:
- To longitudinally track the maturation of MLAERs in normal term infants.
- To determine the optimal stimulus parameters for eliciting stable MLAERs in infants.
- To compare infant MLAERs with adult values.
Main Methods:
- MLAERs were recorded in 21 infants at birth, 6 weeks, 7 months, and 1 year using monaural click stimulation.
- A 70 dBHL stimulus intensity was identified as optimal for waveform definition.
- Waveform stability was assessed across different sleep states and latencies.
Main Results:
- MLAERs showed significant decreases in wave latency with increasing age, reaching adult-like values by 7 months.
- Specific waves (Po, Na, Pa, Nb, Pb, Nc) demonstrated age-related latency reductions.
- Stimulus intensity affected early waves (Po, Na) at term and 6 weeks, but not later waves.
Conclusions:
- Infant auditory pathways undergo rapid development, reflected in MLAER maturation.
- MLAERs provide a sensitive measure of auditory system development from birth through infancy.
- Auditory brainstem function matures significantly within the first year of life.
Abstract:
Middle latency auditory evoked responses (MLAERs) were measured in 21 normal term infants, three to five days after birth and then at 6 weeks, 7 months and 1 year of age. A polyphasic waveform was elicited during natural sleep in all infants at each recording session by monaural click stimulation at a rate of 9 per second. A 70 dBHL stimulus was found to be optimal as the MLAER became less well defined when the stimulus intensity approached the threshold hearing level. The first 60 to 70 msec of the waveform was found to be most stable, with decreasing detectability of peaks at longer latencies. There was no change in wave latency or reproducibility of MLAERs recorded during different sleep states. Waves Po and Na showed a significant decrease in latency with increasing stimulus intensity at term and/or 6 weeks of age. This was not evident for the remainder of the waveform. Waves Po, Na, Pa, Nb, Pb and Nc exhibited significant decreases in latency with age, attaining values indistinguishable from adults by 7 months of age.