Neural systems mediating American sign language: effects of sensory experience and age of acquisition.

ERPs were recorded from deaf and hearing native signers and from hearing subjects who acquired ASL late or not at all as they viewed ASL signs that formed sentences. The results were compared across these groups and with those from hearing subjects reading English sentences. The results suggest that there are constraints on the organization of the neural systems that mediate formal languages and that these are independent of the modality through which language is acquired. These include different specializations of anterior and posterior cortical regions in aspects of grammatical and semantic processing and a bias for the left hemisphere to mediate aspects of mnemonic functions in language. Additionally, the results suggest that the nature and timing of sensory and language experience significantly impact the development of the language systems of the brain. Effects of the early acquisition of ASL include an increased role for the right hemisphere and for parietal cortex and this occurs in both hearing and deaf native signers. An increased role of posterior temporal and occipital areas occurs in deaf native signers only and thus may be attributable to auditory deprivation.

The neurobiology of sensory and language processing in language-impaired children.

Abstract Clinical, behavioral, and neurophysiological studies of developmental language impairment (LI), including reading disability (RD), have variously emphasized different factors that may contribute to this disorder. These include abnormal sensory processing within both the auditory and visual modalities and deficits in linguistic skills and in general cognitive abilities. In this study we employed the event-related brain potential (ERP) technique in a series of studies to probe and compare Merent aspects of functioning within the same sample of LI/RD children. Within the group multiple aspects of processing were affected, but heterogeneously across the sample. ERP components linked to processing within the superior temporal gyrus were abnormal in a subset of children that displayed abnormal performance on an auditory temporal discrimination task. An early component of the visual ERP was reduced in amplitude in the group as a whole. The relevance of this effect to current conceptions of substreams within the visual system is discussed. During a sentence processing task abnormal hemispheric specialization was observed in a subset of children who scored poorly on tests of grammar. By contrast the group as a whole displayed abnormally large responses to words requiring contextual integration. The results imply that multiple factors can contribute to the profile of language impairment and that different and specific deficits occur heterogeneously across populations of LI/RD children.

Comparison of long bones and vertebrae in growing male rats: rate of growth, mineralization, and uptake of 3H-tetracycline at the organ level.

Two vertebral and two long bones of the growing male rat were separated as an intact anatomical unit (at the organ level) and analyzed for mass of dry weight, calcium, and collagen. The rate of growth (mass) and mineralization (uptake of 3H-tetracycline) was determined in rats from 3 to 36 weeks of age. Groups of rats age 3, 6, 8, 10, 14, 20, and 36 weeks were given a single dose of 3H-tetracycline 4 days before sacrifice. Whole bones were assayed for calcium, collagen, and 3H-tetracycline radioactivity. Growth of vertebrae and long bones is similar from 3 to 6 weeks of age. From age 6 to 20 weeks vertebrae grow at a faster rate than long bones. While long bones reach a peak dry mass at 20 weeks of age, the dry mass of vertebrae continues to increase. At ages 3 and 4 weeks, mineralization is significantly higher in vertebrae than in long bones. Peak calcification occurs at 8 weeks for long bones and at 10 weeks for vertebrae. These differences appear to be associated with the difference in age at which closing of growth plates occur as well as differences in formation rates between vertebrae and long bones.