Speech and language development following ... - ResearchGate

C. Ouellet, H. Cohen / Journal of Neurolinguistics 12 (1999) 271±288 273Language development appears to be based on relatively plastic neural systemsthat are also used for other cognitive and perceptual functions [4]. But childrenand adults do not necessarily use the same neural resources for languageperception and production and some parts of the brain may be more active incertain kinds of linguistic activities over time. Locke [37] assigns early vocallearning and utterance acquisition to the right hemisphere whereas, in oldersubjects, the left hemisphere is dominant for everything related to lexicalcomprehension, expression, syntax and grammar tasks. One follow-up study hasshown that the linguistic abilities of a left-hemispherectomized child were similarto those of language-impaired children whereas the linguistic competencies of aright-hemispherectomized child resembled those of language-normal children [75].In the same way, school-age children with left hemisphere lesions show morediculties with language than those with right hemisphere lesions, althoughproblems in language development may occur in both groups. These resultsprovide indirect support for innate specialization and plasticity as well as for theinvolvement of the right hemisphere in language acquisition and verbal cognition[49].Experience may also in¯uence cerebral organization and activity. Dehaene et al.[17] found some anatomical variability in the cortical representation of ®rst andsecond languages. Subjects who listened to stories in their ®rst language showedactivation of the left temporal lobe, especially in the areas along the left superiortemporal sulcus, whereas those who listened to stories in their second languageshowed activity in varying left and right temporal and frontal areas, sometimesrestricted to right hemisphere regions.The central auditory system may also experience a functional reorganizationfollowing changes in auditory stimuli, leading to linguistic improvement [70].Volumetric measurements of the planum temporale, contained in the perisylvianarea, which has been implicated in language development, have revealed that thisarea is already larger on the left than on the right side in the fetal brain.Following auditory deprivation, which results in inactivation of the neurolinguisticmechanisms, a compensatory hypertrophy of the homologous right hemispherestructures may develop as a result of a general neuromaturational delay. The righthemisphere would then control linguistic parameters that were previously underthe left hemisphere's domination. There is a functional shift to intact brainstructures at that time. According to Locke [37], this adaptive but unusual brainorganization produces a functional but imperfect command of language. Pontonet al. [61] suggest instead that the auditory system does not mature withoutstimulation. They showed that the maturational processes of the cortical auditorysystem, which do not progress during a period of deafness, resume after acousticstimulation is reintroduced. However, Truy et al. [80] found that the ascendingauditory pathways remain operational long after prelingual deafness and that theauditory cortex can be activated by electrical stimulations of the cochlea evenwithout perception of environmental sounds. In their study, subjects showedincreased auditory cortex activity during electrical cochlear stimulation.