Do sex hormones influence mean duration of babbling in 5-months-old infants?

Introduction: Minipuberty is a period in early infancy, in which the hypothalamic-pituitary-gonadal axis is activated leading to a secretion of bioactive estradiol and testosterone. It is assumed to affect brain development and, as a result, vocal characteristics. While studies have found hormonal influences on fundamental frequency and articulatory characteristics in infants' crying and babbling, temporal characteristics have not been studied so far. The aim of this study was therefore, as a first step, to investigate the potential influence of sex hormones on the mean duration of babbling vocalizations.

Methods: Blood samples were taken from 20 infants at four, eight and 20 weeks and sex hormone concentrations were measured. The duration of individual infant vocalizations was analyzed from recordings of marginal babbling. A hierarchical, multiple regression approach was used to investigate associations between mean duration and bioactive hormone levels (estradiol (E2), testosterone (T)).

Results: While no estradiol effects were found, the mean duration of an infant's babbling at 20 weeks showed a significant negative association with the corresponding bioactive testosterone concentration in the same infant at the same age (p= 0.003).

Conclusion: The results bolster the assumption that it is not sex per se, which seem to determine prelinguistic development. A better understanding of minipubertal influences is essential both for our understanding of gender-specific brain physiological mechanisms and for the resulting language performance.