Neural encoding of speech sounds in neonates and infants: developmental trajectory and modulating factors

Carles Escera

(1)Cognitive Neuroscience Research Group, Department of Clinical Psychology and Psychobiology, University of Barcelona,

(2)Institute of Neurosciences, University of Barcelona,

(3) Institut de Recerca Sant Joan de Déu (IRSJD), Esplugues de Llobregat, Barcelona

Sites:

www.ub.edu/brainlab

http://www.neurociencies.ub.edu/the-auditory-motor-emotional-and-numerical-brain/

https://www.irsjd.org/ca/recerca/28/neurociencia-cognitiva

ABSTRACT

Infants master their native language with remarkable ease, following a common developmental trajectory across different languages and cultures. There is ample consensus on critical behavioral attainments at given time points during development, such as cooing (1-4 months), babbling (6-10 months) and uttering the first words (12 months). Yet, the underlying neural underpinnings of these language attainments are poorly understood. The acquisition of spoken language requires a sophisticated neural machinery to disentangle the fine-grained spectro-temporal acoustic features differentiating speech sounds. This neural machinery is partially functional in utero, from the 27th gestational week, and keeps its natural maturation processes under genetic, biological, nutritional and environmental influences. From the very same moment of birth, the baby is exposed to a much richer acoustic environment (the mother’s bomb behaves as low-pass filter), fostering rapid experience-dependent plastic changes in the neural encoding of complex sound features, that I will argue, support early language acquisition.

In my talk I will discuss the results of a series of studies carried out in my laboratory with the Frequency-Following Response (FFR), a non-invasive scalp-recorded auditory evoked potential that reflects compound phase-locked neural activity elicited to the spectrotemporal components of the acoustic signal, along the entire auditory hierarchy. These studies have so-far allowed us to establish the standards for recording the neonatal FFR in a hospital routine, to show that fundamental frequency (F0) encoding is adult-like at birth whereas temporal-fine structure encoding shows a striking maturation at the age of one month, to continue to develop up to the age of 6 months, and that fetal conditions challenging normal fetal growth, such as fetal growth restriction of fetal overweight, result in compromised neural encoding of F0 at birth. Furthermore, our results show that the prenatal exposure to environmental music –and to a mono/bilingual acoustic environment- during pregnancy, fosters the neural encoding of speech sounds (F0) at birth. Altogether, these result support the FFR as a powerful to investigate the neural underpinnings of early language acquisition.

Funding. Project PID2021-122255NB-I00 funded by MCIN/AEI/10.13039/501100011033/ FEDER, UE; Fundación Alicia Koplowitz; 2022AR-IRSJDCdTorres; ICREA Acadèmia.