& Language and arithmetic are both lateralized to the left hemisphere in the majority of right-handed adults. Yet, does this similar lateralization reflect a single overall constraint of brain organization, such an overall ‘‘dominance’ ’ of the left hemisphere for all linguistic and symbolic operations? Is it related to the lateralization of specific cerebral subregions? Or is it merely coincidental? To shed light on this issue, we performed a ‘‘colateralization analysis’ ’ over 209 healthy subjects: We investigated whether normal variations in the degree of left hemispheric asymmetry in areas involved in sentence listening and reading are mirrored in the asymmetry of areas involved in mental arithmetic. Within the language network, a region-of-interest analysis disclosed partially dissociated patterns of lateralization, inconsistent with an overall ‘‘dominance’’ model. Only two of these areas presented a lateralization during sentence listening and reading which correlated strongly with the lateralization of two regions active during calculation. Specifically, the profile of asymmetry in the posterior superior temporal sulcus during sentence processing covaried with the asymmetry of calculation-induced activation in the intraparietal sulcus, and a similar colateralization linked the middle frontal gyrus with the superior posterior parietal lobule. Given recent neuroimaging results suggesting a late emergence of hemispheric asymmetries for symbolic arithmetic during childhood, we speculate that these colateralizations might constitute developmental traces of how the acquisition of linguistic symbols affects the cerebral organization of the arithmetic network. &

We present the first direct comparison of language production in brain-injured children and adults, using agecorrected z scores for multiple lexical and grammatical measures. Spontaneous speech samples were elicited in a structured biographical interview from 38 children (5-8 years of age), 24 with congenital left-hemisphere damage (LHD) and 14 with congenital right-hemisphere damage (RHD), compared with 38 age- and gender-matched controls, 21 adults with unilateral injuries (14 LHD, 7 RHD), and 12 adult controls. Adults with LHD showed severe and contrasting profiles of impairment across all measures (including classic differences between fluent and nonfluent aphasia). Adults with RHD (and three nonaphasic adults with LHD) showed fluent but disinhibited and sometimes empty speech. None of these qualitative or quantitative deviations were observed in children with unilateral brain injury, who were in the normal range for their age on all measures. There were no significant differences between children with LHD and RHD on any measure. When LHD children were compared directly with LHD adults using age-corrected z scores, the children scored far better than their adult counterparts on structural measures. These results provide the first systematic confirmation of differential free-speech outcomes in children and adults, and offer strong evidence for neural and behavioral plasticity following early brain damage. For more than 3000 years, we have known that

Abstract: Developmental psychology is ready to blossom into a modern science that focuses on causal mechanistic explanations of development rather than just describing and classifying the skills that children show at different ages. Computational models of cognitive development are formal systems that track the changes in information processing taking place as a behavior is acquired. Models are generally implemented as psychologically constrained computer simulations that learn tasks such as reasoning, categorization, and language. Their principal use is as tools for exploring mechanisms of transition (development) from one level of competence to the next during the course of cognitive development. They have been used to probe questions such as the extent of ‘pre-programmed ’ or innate knowledge that exists in the infant mind, and how the sophistication of reasoning can increase with age and experience. I. Understanding the

In this paper we present DevLex-II, a self-organizing neural network model of early word production. It consists of three self-organizing feature maps (a semantic layer, a phonological layer and a phonemic layer) that are connected via associative links trained by Hebbian learning. We use this model to simulate the early stages of lexical acquisition in children. The simulating results indicate a number of important effects in determining the timing and function of children’s word production, such as word frequency and word length effects. In addition, results from lesioned models indicate developmental plasticity in the network’s recovery from damage. Plasticity occurs at early stages, and changes with time in a non-monotonic and nonlinear fashion. These simulated patterns are due to the nonlinear dynamic properties of the network and match up with data from empirical studies of children.

We report the case of a neonate tested three weeks after a neonatal left sylvian infarct. We studied her perception of speech and non-speech stimuli with high-density event-related potentials. The results show that she was able to discriminate not only a change of timbre in tones but also a vowel change, and even a place of articulation contrast in stop consonants. Moreover, a discrimination response to stop consonants was observed even when syllables were produced by di#erent speakers. Her intact right hemisphere was thus able to extract relevant phonetic information in spite of irrelevant acoustic variation. These results suggest that both hemispheres contribute to phoneme perception during the first months of life and confirm our previous findings concerning bilateral responses in normal infants.

sensitivity in children with early focal brain injury and children with specific language impairment

Speech processing in adults relies on precise and specialized networks, located primarily in the left hemisphere. Behavioural studies in infants indicate that a considerable amount of language learning already takes place in the first year of life in the domains of phonology, prosody, and word segmentation. Thanks to the progress of neuro-imaging, we can move beyond behavioural methods and examine how the infant’s brain processes verbal stimuli before learning. These studies reveal a structural and functional organization close to what is described in adults and suggest a strong bias for speech processing in these regions that might guide infants in the discovery of the properties of their native language, although no evidence can be provided as yet for speech specificity of such networks.

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A neuroconstructivist approach