Cerebral hemodynamics in newborn infants exposed to speech sounds: A whole‐head optical topography study

Abstract

Considerable knowledge on neural development related to speech perception has been obtained by functional imaging studies using near-infrared spectroscopy (optical topography). In particular, a pioneering study showed stronger left-dominant activation in the temporal lobe for (normal) forward speech (FW) than for (reversed) backward speech (BW) in neonates. However, it is unclear whether this stronger left-dominant activation for FW is equally observed for any language or is clearer for the mother tongue. We hypothesized that the maternal language elicits clearer activation than a foreign language in newborns because of their prenatal and/or few-day postnatal exposure to the maternal language. To test this hypothesis, we developed a whole-head optode cap for 72-channel optical topography and visualized the spatiotemporal hemodynamics in the brains of 17 Japanese newborns when they were exposed to FW and BW in their maternal language (Japanese) and in a foreign language (English). Statistical analysis showed that all sound stimuli together induced significant activation in the bilateral temporal regions and the frontal region. They also showed that the left temporal-parietal region was significantly more active for Japanese FW than Japanese BW or English FW, while no significant difference between FW and BW was shown for English. This supports our hypothesis and suggests that the few-day-old brain begins to become attuned to the maternal language. Together with a finding of equivalent activation for all sound stimuli in the adjacent measurement positions in the temporal region, these findings further clarify the functional organization of the neonatal brain.

Evaluating signal-correlated noise as a control task with language-related gamma activity on electrocorticography

“…We previously attempted to validate reverse (or backward) speech as a control task in studies of auditory language with electrocorticography (ECoG) (Brown et al, 2012), the intracranial counterpart to EEG. In many fMRI studies, such time reversed speech is utilized to control for non-language-specific auditory activities (Gherri and Eimer, 2011, Moore-Parks et al, 2010, Perani et al, 1996, Redcay and Courchesne, 2008, Redcay et al, 2008, Sato et al, 2012). These studies commonly report that the blood-oxygen-level-dependent signal detected by fMRI is enhanced within peri-Sylvian regions during forward speech compared to reverse speech, supporting the notion that reverse speech controls for non-language-specific auditory functions.…”

Hemoglobin phase of oxygenation and deoxygenation in early brain development measured using fNIRS

“…The typical hemodynamic response to neural activation consists of an increase in oxy-Hb and an almost antiphase decrease in deoxy-Hb. As a method of neuroimaging, functional NIRS (fNIRS) has been used to reveal the hemodynamic response to stimulus-induced cortical activation in young infants (17)(18)(19)(20)(21) and preterm infants (22). fNIRS has also been used to study the functional connectivity of the cortex using temporal correlations of spontaneous low-frequency oscillations (less than 0.1 Hz) of the Hb signals in multiple regions of the cortex in infants (23)(24)(25).…”

Biological Preconditions for Language Development

“…Neuroimaging studies during the first 3 months of life comparing language stimuli with acoustically matched nonlanguage stimuli have shown left-hemispheric activation for language in similar fronto-temporal brain regions as was found for adult language processing (Dehaene-Lambertz et al, 2002;Peña et al, 2003). Furthermore, the native language was specifically shown to already elicit left-hemispheric activation a few days after birth (Sato et al, 2012). Nonetheless, the infant language network may be at an immature stage.…”