Large-scale brain networks underlying language acquisition in early infancy.

Area of Science:

• Developmental Neuroscience
• Cognitive Neuroscience
• Infant Brain Development

Background:

• Understanding early language acquisition is crucial for human development.
• The functional connectivity of language-related brain regions in preverbal infants remains an open question.

Purpose of the Study:

• To investigate the functional brain networks in 3-month-old infants during speech sound presentation.
• To determine if language-related areas in the frontal and temporal regions form a functional network in preverbal infants.

Main Methods:

• Utilized 94-channel near-infrared spectroscopy (NIRS) on sleeping 3-month-old infants.
• Measured brain activity during spontaneous periods and periods with Japanese sentence stimuli.
• Analyzed functional connectivity using time-lagged cross-correlations and coherences of oxygenated hemoglobin (oxy-Hb) signals.

Main Results:

• Speech sound presentation led to increased oxygenated hemoglobin in bilateral temporal, temporoparietal, prefrontal, and occipital regions.
• Functional connectivity analysis revealed high correlations in neighboring and contralateral homologous channels.
• Post-stimulus period showed enhanced ipsilateral connectivity, particularly anterior-posterior, and a stronger frontal-temporal relationship, indicating a hysteresis effect.

Conclusions:

• The frontal and temporal regions form functional networks in infants, exhibiting memory of previous auditory input (hysteresis).
• Spatiotemporally large-scale brain networks, including frontal and temporal regions, are hypothesized to underlie infant speech processing.
• These early-developing networks may play a critical role in subsequent language acquisition.