Atypical neural oscillations in response to speech in infants and children with speech and language impairments: a systematic review

Abstract Purpose: A growing body of evidence suggests that speech perception impairments found in subjects with language deficits could be linked to the atypical neural entrainment of the brain oscillations present in the auditory cortex and oscillating at different frequencies, to the amplitude modulations of speech at different rates (i.e. phrase-level, syllable-level, phoneme-level). Material and methods: In this paper, we conducted a systematic review of the studies investigating the neural synchronisation to auditory stimuli, linguistic or non-linguistic, in subjects with or at risk for language impairments. Our systematic research led to thirteen articles. The majority of these studies concerned subjects with dyslexia. Results: The studies are in favour of an overall atypical oscillatory activity of the auditory cortex in response to speech, at different modulation rates, associated with language outcomes. However, this systematic review shows that this research area is at its infancy and that conflicting results on the precise oscillatory mechanisms involved in the impaired speech perception still exist; further research as well as replications of the previous findings are needed to better understand the relationship between atypical neural entrainment to speech and language disorders. Conclusion: In conclusion, we link this systematic review to the prosodic prenatal shaping hypothesis proposing a developmental framework of speech perception linked to the theory of the embedded neural oscillations of the auditory cortex. A better understanding of the development of the neural mechanisms underlying speech perception and how they develop during infancy and childhood, both in typically and atypically developing children, could lead to better and earlier screening of children at risk for Language-Learning Impairment (LLI) and thus earlier and more efficient intervention programs.