The frequency-following response in late preterm neonates: a pilot study

Abstract

Introduction: Infants born very early preterm are at high risk of language delays. However, less is known about the consequences of late prematurity. Hence, the aim of the present study is to characterize the neural encoding of speech sounds in late preterm neonates in comparison with those born at term.

Methods: The speech-evoked frequency-following response (FFR) was recorded to a consonant-vowel stimulus /da/ in 36 neonates in three different groups: 12 preterm neonates [mean gestational age (GA) 36.05 weeks], 12 "early term neonates" (mean GA 38.3 weeks), and "late term neonates" (mean GA 41.01 weeks).

Results: From the FFR recordings, a delayed neural response and a weaker stimulus F₀ encoding in premature neonates compared to neonates born at term was observed. No differences in the response time onset nor in stimulus F₀ encoding were observed between the two groups of neonates born at term. No differences between the three groups were observed in the neural encoding of the stimulus temporal fine structure.

Discussion: These results highlight alterations in the neural encoding of speech sounds related to prematurity, which were present for the stimulus F₀ but not for its temporal fine structure.

Keywords: FFR; infants; language; preterm; speech-ABR.

Figure 1

(A) Grand-averaged click ABRs for preterm neonates (PRE, red), early at term neonates (EARLY, green) and late at term neonates (LATE, blue), with the wave V peak pointed out. Data distribution (violin plots) for (B) wave V amplitude and (C) its latency. The black horizontal line illustrates the median and the black vertical line delimits the interquartile range (IQR).

Figure 2

Temporal and spectral neural representation of the consonant-vowel /da/ in the neonate’s auditory brain. (A) Grand-averaged FFR waveforms and ampltude FFR spectra extracted from the consonant transition and from the vowel regions after averaged neural response polarities; and (B) after subtracted neural response polarities from preterm neonates (PRE, red), early at term neonates (EARLY, green) and late at term neonates (LATE, blue). The signal (s) and noise (n) spectral windows used for FFR quantification are marked with dark and light gray rectangles, respectively.

Figure 3

Data distribution (violin plots) of the (A) pre-stimulus RMS; (B) neural lag; (C,D) spectral amplitude at fundamental frequency (F₀) and first formant (F₁) extracted from the consonant transition and (E,F) from the vowel. The layout is the same to that used in Figures 1B,C.