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Language and brain development

The brain is divided into two hemispheres - the left and right - which specialize in different functions. The hemispheres communicate via the corpus callosum. Tests have shown increased neural activity in parts of the left hemisphere during language use, and temporarily disrupting the left hemisphere's blood flow also disrupts language skills. From a very early age in the womb, the brain shows lateralization of language functions to the left hemisphere.

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THE BRAIN
The brain is divided into two celebral hemispheres: *Left hemisphere *Right hemisphere Each hemisphere appears to be specialized for some behaviors. The hemispheres communicate with each other through a thick band of 200-250 million nerve fibers called the corpus callosum.
front Corpus Callosum Left Hemi- sphere Right Hemis phere Cortex White Matter
How do we know that the left hemisphere controls language in most adults? A. Tests have demonstrated increased neural activity in parts of the left hemisphere when subjects are using language. (PET scans--Positron Emission Tomography, where patient injects mildly radioactive substance, which is absorbed more quickly by the more active areas of the brain). B. In 1949 it was discovered that if sodium amytal is injected into the left carotid artery, which services blood to the left hemisphere, language skills are temporarily disrupted. If the entire left hemisphere is put to sleep, a person can think but cannot talk.
LANGUAGE AND BRAIN DEVELOPMENT Numerous neurolinguistic studies have found that the way the brain is organized for language and grammar in the adult is already reflected in the brains of newborns and young infants—even before they have entered the period during which language actively develops. Lateralization of language to the left hemisphere is a process that begins very early in life. For example, Wernicke’s area is visibly distinctive in the left hemisphere of the fetus by the twenty-sixth gestational week. Moreover, infants show evidence of many of the neural correlates of linguistic categories that we observe in adults.
BRAIN PLASTICITY While the left hemisphere is innately predisposed to specialize for language, there is also evidence of considerable plasticity (i.e., flexibility) in the system during the early stages of language development. This means that under certain circumstances, the right hemisphere can take over many of the language functions that would normally reside in the left hemisphere. Hemispherectomy, in which one hemisphere of the brain is surgically removed. This procedure is used to treat otherwise intractable cases of epilepsy.
CRITICAL PERIOD Children do not require explicit language instruction, but they do need exposure to language to develop normally. The critical-age hypothesis asserts that language is biologically based and that the ability to learn a native language develops within a fixed period, from birth to middle childhood. During this critical period, language acquisition proceeds easily, swiftly, and without external intervention. After this period, the acquisition of grammar is difficult and, for most individuals, never fully achieved. Children deprived of language during this critical period show atypical patterns of brain lateralization.