Poster E54, Saturday, August 18, 3:00 – 4:45 pm, Room 2000AB

Early interactive acoustic experience with non-speech modulates phase synchronization of evoked gamma to speech at 18-months-of-age

Silvia Ortiz-Mantilla1, Teresa Realpe-Bonilla1, April A Benasich1;1Center for Molecular and Behavioral Neuroscience, Rutgers University Newark, NJ, USA

Over the first year of life, infants establish the foundations for learning their native language by constructing language-specific phonemic maps within auditory cortex. It has been widely demonstrated that cortical effects of sensory input are continuously modified by both maturation and experience. During early development the auditory cortex is highly plastic, making infancy a privileged period for optimizing language mapping. We have shown that interactive acoustic experience (between 4- and 6-months-of-age) with temporally modulated non-speech stimuli containing acoustic cues important for speech, enhances the efficiency of infants' acoustic processing of both trained and novel untrained non-speech at 7-months-of-age (Benasich et al., 2014). Neural mechanisms underlying these training effects were also investigated through measures of oscillatory power -- infants who underwent an early interactive experience displayed a left lateralized increase in gamma power during tone discrimination (Musacchia et al., 2017). Furthermore, at 9-months-of-age, infants who participated in the interactive acoustic experience showed an increase in high-gamma power in auditory cortices, suggesting that early auditory engagement might facilitate establishment of enduring phonemic representations (Ortiz-Mantilla et al., 2018). In this study we examined the longitudinal impact of interactive non-speech auditory experience on processing of speech syllables at 18-months-of-age. Infants were presented with a consonant-vowel contrast varying in voice-onset time (da/ta) using a passive oddball paradigm and then compared to a cross-sectional group of 18-month-old naïve controls with no such experience. Dense-array EEG (124-sensor net) was collected and mapped onto age-appropriate brain templates. Source modeling placed dipoles in both auditory cortices. Temporal-spectral analyses were conducted in source space, within the 2 to 90Hz frequency range, using 1Hz-wide frequency bins and time resolution of 50ms. Phase coherence was evaluated by examining consistency of phase alignment across trials using inter-trial phase locking (ITPL). Permutation testing identified clusters of significance between the groups for processing of the standard stimulus. We found that infants with previous acoustic experience display greater gamma phase synchronization in left auditory cortex than naïve controls. These results demonstrate that experience-dependent effects that generalized to speech at 9-months (Ortiz-Mantilla et al., 2018) continue to have an effect on processing at 18-months of age. This is clearly shown in response to the standard stimulus, which is critical to the construction of cortical maps that support rapid discrimination of incoming deviant stimuli. Early gamma responses, that tend to be time- and phase-locked to transient auditory stimuli (evoked gamma), reflect engagement of the sensory auditory cortex in stimulus processing, and have been proposed to index learning and experience in the auditory cortex. Our results suggest that active auditory experience may confer a significant speech processing advantage, by providing more temporal stability of the oscillatory gamma responses across trials. Interactive non-speech auditory experience might therefore, facilitate neural plasticity and support more efficient processing of speech in the left auditory cortex during the time infants are acquiring their native language.

Topic Area: Language Development