Neural dynamics of the motor system in speech perception

Abstract

The role of the motor system in speech perception has provoked considerable debate over the past 50 years. Motor and sensory cortices are traditionally thought to be functionally separate systems. However, many studies have shown their roles in both action and perception to be highly integrated. In particular, this has been observed in regard to speech, where listening to speech sounds elicits neural activity in motor regions of the brain in both adults and infants. The primary goal of the present study was to investigate the role of motor and motor planning brain regions in speech perception throughout various stages of language development. Three datasets containing magnetoencephalography (MEG) data from 2-, 6-, 7-, and 11-month-old infants and adults were used to address four experimental questions related to the role that motor brain systems play in the auditory perception of speech. The four experimental questions examine the relationship between activation in auditory sensory and motor regions of the brain with respect to: 1) the temporal structure of activation in sensory as opposed to motor brain regions, 2) the development of neural responses with increasing age, 3) the role of language experience, and 4) potential differences between speech as opposed to nonspeech auditory signals. Results showed that motor and motor planning regions are activated during speech perception across all ages. At 2 months of age, infants show activity in both motor and motor planning regions in response to speech, but not to nonspeech acoustic stimuli. This provides evidence that infants’ activation of sensory and motor brain regions in response to speech does not require experience producing speech.