Neural specialization of phonological and semantic processing in young children

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Abstract

<p id="d3108060e195">This study aimed to examine early specialization of brain regions for phonological and semantic processing of spoken language in young children. Thirty‐five typically developing children aged from 5 to 6 years performed auditory phonological (same sound judgment) and semantic (related meaning judgment) word‐level tasks. Using functional magnetic resonance imaging, we examined specialization within the language network, by conducting three levels of analysis. First, we directly compared activation between tasks and found a greater sound judgment as compared to meaning judgment activation in left superior temporal gyrus (STG) and supramarginal gyrus. In contrast, greater meaning judgment as compared to sound judgment task activation was found in left middle temporal gyrus (MTG). Second, we examined the brain‐behavior correlations and found that phonological skill was correlated with the task difference in activation in left superior temporal sulcus, whereas semantic skill was correlated with the task difference in activation in left MTG. Third, we compared between two experimental conditions within each task and found a parametric effect in left STG for the sound judgment task, and a parametric effect in left MTG for the meaning judgment task. The results of this study indicate that, by the age of 5–6 years, typically developing children already show some specialization of temporo‐parietal brain regions for phonological and semantic processes. However, there were no task differences in the left inferior frontal gyrus suggesting that the frontal cortex may not yet be specialized in this age range, which is consistent with the delayed maturation of the frontal cortex. </p>

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Meta-analyzing left hemisphere language areas: phonology, semantics, and sentence processing.

M Vigneau, V Beaucousin, P Hervé … (2006)

The advent of functional neuroimaging has allowed tremendous advances in our understanding of brain-language relationships, in addition to generating substantial empirical data on this subject in the form of thousands of activation peak coordinates reported in a decade of language studies. We performed a large-scale meta-analysis of this literature, aimed at defining the composition of the phonological, semantic, and sentence processing networks in the frontal, temporal, and inferior parietal regions of the left cerebral hemisphere. For each of these language components, activation peaks issued from relevant component-specific contrasts were submitted to a spatial clustering algorithm, which gathered activation peaks on the basis of their relative distance in the MNI space. From a sample of 730 activation peaks extracted from 129 scientific reports selected among 260, we isolated 30 activation clusters, defining the functional fields constituting three distributed networks of frontal and temporal areas and revealing the functional organization of the left hemisphere for language. The functional role of each activation cluster is discussed based on the nature of the tasks in which it was involved. This meta-analysis sheds light on several contemporary issues, notably on the fine-scale functional architecture of the inferior frontal gyrus for phonological and semantic processing, the evidence for an elementary audio-motor loop involved in both comprehension and production of syllables including the primary auditory areas and the motor mouth area, evidence of areas of overlap between phonological and semantic processing, in particular at the location of the selective human voice area that was the seat of partial overlap of the three language components, the evidence of a cortical area in the pars opercularis of the inferior frontal gyrus dedicated to syntactic processing and in the posterior part of the superior temporal gyrus a region selectively activated by sentence and text processing, and the hypothesis that different working memory perception-actions loops are identifiable for the different language components. These results argue for large-scale architecture networks rather than modular organization of language in the left hemisphere.

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At 6-9 months, human infants know the meanings of many common nouns.

E. Bergelson, D. Swingley (2012)

It is widely accepted that infants begin learning their native language not by learning words, but by discovering features of the speech signal: consonants, vowels, and combinations of these sounds. Learning to understand words, as opposed to just perceiving their sounds, is said to come later, between 9 and 15 mo of age, when infants develop a capacity for interpreting others' goals and intentions. Here, we demonstrate that this consensus about the developmental sequence of human language learning is flawed: in fact, infants already know the meanings of several common words from the age of 6 mo onward. We presented 6- to 9-mo-old infants with sets of pictures to view while their parent named a picture in each set. Over this entire age range, infants directed their gaze to the named pictures, indicating their understanding of spoken words. Because the words were not trained in the laboratory, the results show that even young infants learn ordinary words through daily experience with language. This surprising accomplishment indicates that, contrary to prevailing beliefs, either infants can already grasp the referential intentions of adults at 6 mo or infants can learn words before this ability emerges. The precocious discovery of word meanings suggests a perspective in which learning vocabulary and learning the sound structure of spoken language go hand in hand as language acquisition begins.

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Dyslexia (specific reading disability).

B Shaywitz, S Shaywitz (2005)

Converging evidence from a number of lines of investigation indicates that dyslexia represents a disorder within the language system and more specifically within a particular subcomponent of that system, phonological processing. Recent advances in imaging technology, particularly the development of functional magnetic resonance imaging, provide evidence of a neurobiological signature for dyslexia, specifically a disruption of two left hemisphere posterior brain systems, one parieto-temporal, the other occipito-temporal, with compensatory engagement of anterior systems around the inferior frontal gyrus and a posterior (right occipito-temporal) system. Furthermore, good evidence indicates a computational role for the left occipito-temporal system: the development of fluent (automatic) reading. The brain systems for reading are malleable and their disruption in dyslexic children may be remediated by provision of an evidence-based, effective reading intervention. In addition, functional magnetic resonance imaging studies of young adults with reading difficulties followed prospectively and longitudinally from age 5 through their mid twenties suggests that there may be two types of reading difficulties, one primarily on a genetic basis, the other, and far more common, reflecting environmental influences. These studies offer the promise for more precise identification and effective management of dyslexia in children, adolescents and adults.