Neural markers of early phoneme learning in infants: a systematic review of EEG evidence on brain development

This research provides a detailed map of early human auditory development, tracking the brain's journey from the third trimester of pregnancy through the first two years of postnatal life. We now know that the brain is already wired to tell the difference between speech sounds as early as the 30th week of pregnancy, long before a baby ever hears their first words in the outside world. By the time they are born, infants possess an amazing built-in ability to recognize and process speech, even while they are fast asleep. This rapid progress is powered by a biological engine where the brain’s physical structure matures in perfect harmony with its ability to process sound. As the brain’s protective white matter (myelin) grows and nerve signals travel faster, a change we can actually see in the speed of specific brain-wave components like the P2 or iP1. This complex system relies on a delicate balance: while the left side of the brain handles quick and detailed sound changes, the right side tunes into the slower, rhythmic patterns of speech. While babies are born with a natural sensitivity to sound, it is their active engagement with the world that really shapes their internal acoustic maps, not just passive listening. These early neural signatures serve as biomarkers that can predict the development of a child. By looking at how a newborn responds to speech or checking for specific patterns like gamma power, researchers can identify early signs of dyslexia, language delays or autism traits right at the beginning of life. Even though we still face technical limitations like limited image clarity or the difficulty of following families over many years, these findings suggest a future where early brain scans become routine screening tools. This would allow us to provide support during the most plastic window of a child's brain development, giving every infant the best possible start.