Sound envelope processing in the developing human brain: a MEG study

Objective: This study investigated auditory cortical processing of linguistically-relevant temporal modulations in the developing brains of young children. Methods: Auditory envelope following responses to white noise amplitude modulated at rates of 1-80 Hz in healthy children (aged 3-years) and adults were recorded using a paediatric magnetoencephalography (MEG) system and a conventional MEG system, respectively. Results: For children, there were envelope following responses to slow modulations but no significant responses to rates higher than about 25 Hz, whereas adults showed significant envelope following responses to almost the entire range of stimulus rates. Conclusion: Our results show that the auditory cortex of preschool-aged children has a sharply limited capacity to process rapid amplitude modulations in sounds, as compared to the auditory cortex of adults. Significance: These neurophysiological results are consistent with previous psychophysical evidence for a protracted maturational time course for auditory temporal processing. The findings are also in good agreement with current linguistic theories that posit a perceptual bias for low frequency temporal information in speech during language acquisition. These insights also have clinical relevance for our understanding of language disorders that are associated with difficulties in processing temporal information in speech.