Mismatch negativity indicates vowel discrimination in newborns

431

327

The ability to learn language is a human trait. In adults and children, brain imaging studies have shown that auditory language activates a bilateral frontotemporal network with a left hemispheric dominance. It is an open question whether these activations represent the complete neural basis for language present at birth. Here we demonstrate that in 2-d-old infants, the language-related neural substrate is fully active in both hemispheres with a preponderance in the right auditory cortex. Functional and structural connectivities within this neural network, however, are immature, with strong connectivities only between the two hemispheres, contrasting with the adult pattern of prevalent intrahemispheric connectivities. Thus, although the brain responds to spoken language already at birth, thereby providing a strong biological basis to acquire language, progressive maturation of intrahemispheric functional connectivity is yet to be established with language exposure as the brain develops

mentioning

confidence: 99%

Neural language networks at birth

Perani

Saccuman

Scifo

et al. 2011

431

327

“…In contrast, both groups should show similar MMRs for a vowel identity change, previously observed in newborns (30,31), because both groups had heard vowels in utero, being surrounded by the Finnish language environment, which is rich in vowels (32).…”

mentioning

confidence: 75%

Learning-induced neural plasticity of speech processing before birth

Partanen

Kujala

Näätänen

et al. 2013

197

146

Learning, the foundation of adaptive and intelligent behavior, is based on plastic changes in neural assemblies, reflected by the modulation of electric brain responses. In infancy, auditory learning implicates the formation and strengthening of neural long-term memory traces, improving discrimination skills, in particular those forming the prerequisites for speech perception and understanding. Although previous behavioral observations show that newborns react differentially to unfamiliar sounds vs. familiar sound material that they were exposed to as fetuses, the neural basis of fetal learning has not thus far been investigated. Here we demonstrate direct neural correlates of human fetal learning of speech-like auditory stimuli. We presented variants of words to fetuses; unlike infants with no exposure to these stimuli, the exposed fetuses showed enhanced brain activity (mismatch responses) in response to pitch changes for the trained variants after birth. Furthermore, a significant correlation existed between the amount of prenatal exposure and brain activity, with greater activity being associated with a higher amount of prenatal speech exposure. Moreover, the learning effect was generalized to other types of similar speech sounds not included in the training material. Consequently, our results indicate neural commitment specifically tuned to the speech features heard before birth and their memory representations. mismatch negativity | event-related potentials D uring the fetal period the brain undergoes extensive developmental changes as new synapses are formed (1) and axonal connections between neurons are myelinated (2), facilitating efficient recognition and analysis of complex information. In audition, the functional maturation of the developing nervous system is driven by external input, which is evidenced by, for instance, the rapid reorganization of the auditory cortex by external stimuli soon after the onset of hearing in rats (3). This was suggested to occur in humans usually by the gestational age of 27 wk (4). Such plastic changes in neural assemblies during early development indicate that humans have some learning capability even before birth (5, 6). However, this learning capability may be based predominantly on the discrimination of low-pitched sounds that can penetrate the intrauterine walls (7-9). This lowpitch information may play an important role in early speech discrimination of newborns (10) by facilitating learning to segment incoming speech into meaningful units.Consistent with this, previous behavioral studies have shown that fetuses become attuned to a variety of features of the surrounding auditory environment. For example, fetuses habituate to the native language of the environment or of the mother (11, 12), familiar melodies (13) or fragments of stories heard during pregnancy (14), and even the mother's voice (15). In addition to learning-based habituation involving the laterobasal amygdala only (16), fetuses, for example, react differently to native and nonnative vowels (17) or f...

“…In fact, newborns appear to discriminate all phonetic contrasts of the languages of the world, including those that their parents can no longer distinguish. Newborns distinguish consonants differing in one feature-for example, place of articulation, voicing, manner of articulation (9)(10)(11), duration (12)-as well as vowel quality contrasts (13,14). Do the representations newborns hold in memory contain the full range of segmental details suggested by these discrimination capacities?…”

mentioning

confidence: 99%

Newborn’s brain activity signals the origin of word memories

Benavides-Varela

Hochmann

Montorsi

et al. 2012

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 materialshowed 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.neonate's memory | right frontal lobe | sound encoding | speech perception | oxyhemoglobin P revious studies have shown that newborns and human fetuses are able to remember word sounds (1-3) as well as to extract prosodic properties of speech (4) or identity relations between syllables (5, 6). However, neither the specific elements newborns encode from speech, nor the brain structures that mediate speech recognition at birth have been precisely characterized. Building on a functional near-infrared spectroscopy (fNIRS) paradigm used to test memory in newborns (7), the present study asks whether the newborn can remember all of the sounds [consonants (C) and vowels (V)] that form a bisyllabic CVCV word, or whether some of these segments are better encoded than others.Judging by the number of studies reporting early abilities to discriminate fine phonetic contrasts (8), one might be inclined to ascribe to newborns a very detailed representation of the sound of words. In fact, newborns appear to discriminate all phonetic contrasts of the languages of the world, including those that their parents can no longer distinguish. Newborns distinguish consonants differing in one feature-for example, place of articulation, voicing, manner of articulation (9-11), duration (12)-as well as vowel quality contrasts (13,14). Do the representations newborns hold in memory contain the full range of segmental details suggested by these discrimination capacities?Different studies suggest that in adults (15-18), and in infants older than 12 mo (19-23), consonantal sequences are encoded more robustly than vocalic sequences for the representation of words. It is possible that a similar bias (namely, preference for consonantal information when encodi...