Neurophysiology
ABR. Typical ABRs were
observed in all neonates. Grand-average waveforms, and wave V amplitude
and latency distributions are illustrated in Figure 1. Statistical
analyses (Table 3) revealed that wave V amplitude was smaller in LGA
compared to AGA neonates (P = .01). However, after normalization
by the pre-stimulus neural activity, these differences washed out
(P = .23). No group differences were observed in wave V peak
latency (P = .07).
FFR. As it can be seen in Figure 2, the FFR is a
neurophysiological response that reflects the neural encoding of the
eliciting sound with striking faithfulness. Clear FFR waveforms were
recorded in both groups, LGA and AGA, although in the LGA group a
notably smaller amplitude through the entire FFR duration was observed
compared to the AGA group (Figure 2B). Notice, however, that the
background EEG was similar in the two groups (no group differences in
pre-stimulus RMS: P = .75; Figure 3A; Table 3). Neural lag was
also comparable across groups (P = .10; Figure 3B; Table 3).
To quantify the FFR, the F0 spectral amplitude and its
normalization (SNR) were retrieved by means of the FFT for the responses
to both the stimulus consonant transition and the vowel regions in each
group (Figure 2C; Figure 3C to F). Smaller spectral amplitudes were
found in LGA compared to the AGA group for the
consonant transition (P =
.002) and the vowel regions (P = .008). Similar results were
obtained after normalization (i.e., after retrieving the FFR’s SNR),
showing that the LGA group had a smaller SNR than the AGA group in both
regions (consonant transition region: P = .01; vowel region:P = .005).
To further characterize our data, we tested whether our results could be
explained by the neonates’ adipose tissue. For that, a matrix of
correlations between neonatal BMI and all FFR parameters was computed
across the entire final sample (N = 50, see Figure 4). Strong
significant correlations between neonatal BMI and spectral amplitude for
the consonant transition (r = -0.54, P <.001)
and for the vowel region (r = -0.57, P <.001)
were found, as well as with the normalized spectral amplitude (SNR) for
the vowel region (ρ = -0.42, P = .004) (Figure 4). In line
with previous literature in which a significant relation was observed
between maternal pre-gestational BMI and/or gestational weight gain
(GWG) and offspring cognitive outcomes66,67, we
carried out an identical statistical approach replacing the neonatal
variable with the maternal variables. These analyses yielded no
significant correlations.