Newborn's brain activity signals the origin of word memories

Abstract

Recent research has shown that specific areas of the human brain are activated by speech from the time of birth. However, it is currently unknown whether newborns' brains also encode and remember the sounds of words when processing speech. The present study investigates the type of information that newborns retain when they hear words and the brain structures that support word-sound recognition. Forty-four healthy newborns were tested with the functional near-infrared spectroscopy method to establish their ability to memorize the sound of a word and distinguish it from a phonetically similar one, 2 min after encoding. Right frontal regions--comparable to those activated in adults during retrieval of verbal material--showed a characteristic neural signature of recognition when newborns listened to a test word that had the same vowel of a previously heard word. In contrast, a characteristic novelty response was found when a test word had different vowels than the familiar word, despite having the same consonants. These results indicate that the information carried by vowels is better recognized by newborns than the information carried by consonants. Moreover, these data suggest that right frontal areas may support the recognition of speech sequences from the very first stages of language acquisition.

Fig. 1.

Details of the procedure used in the study. (A) Location of channels (gray squares) and regions of interest (white ellipses) on a schematic neonate brain. (B) The experimental design. Each rectangle represents a block consisting in a series of six words separated by short pauses of 0.5 or 1.5 s.

Fig. 2.

Time course of the relative hemodynamic changes in the right frontal area averaged across subjects per group. (A) Mean concentration changes across the experiment. The x axis shows number of blocks. (B) Hemodynamic curve in the last block of the familiarization phase and (C) first block of the test phase. The x axis displays time in seconds. The rectangle along the x axis indicates the time of stimulation. In all of the graphs, the y axis shows the changes in concentration of oxyhemoglobin in mmol⋅mm. Error bars indicate SEM (permutation test, **P < 0.001).

Fig. 3.

Oxyhemoglobin concentration changes from the last block of familiarization to the first block of the test phase. Channels located in the right frontal, left temporal, and right parietal areas showed a decrement in oxyhemoglobin when participants heard a test word that shared the same vocalic-tier of the familiarization word but had different consonantal-tier (white bar). In contrast, there was an increment in the concentration of oxyhemoglobin from the familiarization to the test when neonates heard a word containing the same consonantal content of the familiarization word but novel vowels (black bar). Colored ellipses on the schematic neonate brain indicate the localization of the channels included in the ROI. Error bars indicate SEM (t test, ***P < 0.0001; *P < 0.05).