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Language Has Both Learned and Innate Components Humans have highly specialized language in which arbitrary symbols or behaviors are assembled and reassembled in almost infinite. All languages have similar basic elements: • Phonemes—basic speech sounds • Morphemes—simple units of meaning • Semantics—meanings of words or sentences • Syntax—grammatical rules for constructing phrases and sentences From birth, babies can distinguish phonemes from any language. Language development depends on experience during a sensitive period, a time when an organism can be permanently altered by a particular experience or treatment. Effects of Isolation on Birdsong Development Song Control Nuclei of the Songbird Brain Elicitation of Vocalizations by Electrical Stimulation of the Monkey Brain Language Has Both Learned and Innate Components Chimpanzees and gorillas can learn other systems of communication: • American Sign Language (ASL) • Use arbitrary colored tokens or computerized symbols in ways that seem to reflect an acquired ability to form short “sentences”—novel, meaningful chains made up of basic units of meaning. • Kanzi (a bonobo) learned to use symbols in novel ways through observational learning rather than through intense training. Chimpanzee Using Symbols American Sign Language A Heritable Language Disorder Language Disorders Result from Region-Specific Brain Disorders M. Leborgne could only utter the syllable “tan” after a brain injury. Study of this brain and similar cases led Paul Broca to identify a region in the anterior left hemisphere that is specialized for speech. Broca’s area—region of the inferior frontal lobe that is involved in speech production Aphasia—an impairment in language ability caused by brain injury, usually to the left hemisphere The Wada test determines involvement of hemispheres in language by anesthetizing each hemisphere separately using sodium amytal. The Brain of “Tan” The Wada Test Language Disorders Result from Region-Specific Brain Disorders Prominent signs of aphasia: Paraphasia—substitution for a word by a sound, incorrect word, or unintended word Neologism—an entirely novel nonsense word Nonfluent speech—talking with considerable effort, in short sentences, and without the usual melodic character of conversational speech Many patients with aphasia may also show other impairments: • Agraphia—inability to write • Alexia—inability to read • Apraxia—a motor impairment in the ability to begin and execute skilled voluntary movements, even though there is no muscle paralysis. Brain Lesions That Produce Aphasia Language Symptomatology in Aphasia Cortical Speech and Language Areas in Humans PET Scans of Brain Activation in Progressively More-Complex Language Tasks Functional Neuroimaging Tracks Activity in the Brain’s Language Zones Word processing has different levels: 1. Passive exposure to seen words (posterior area of left hemisphere) 2. Passive exposure to spoken words (temporal lobes) 3. Oral repetition (motor cortex of both sides, the supplementary motor cortex, and a portion of the cerebellum and insular cortex) 4. Generation of a semantic association to a word (language-related regions in the left hemisphere, including Broca’s area) Electrical Stimulation of Some Brain Sites Can Interfere with Language Mapping Language Areas “invasive pre-surgery mapping techniques, such as electrocortical stimulation (bottom), which requires a patient to be awake and conversant while surgeons probe exposed brain areas in an effort to locate and map language-related functions.” Better brain imaging helps surgeons avoid damage to language functions November 4, 2003 By Gerry Everding http://news.wustl.edu/news/Pages/494.aspx The Traditional Connectionist Model of Aphasia Towards a New Neurobiology of Language • Neurobiological measures to study language • deficit-lesion correlations in stroke patients • electrophysiological data from electroencephalographic • intracranial recordings associated with surgical interventions • Wada test for language lateralization • The “classical model” of language • Based on Broca, Wernicke and Lichtheim • Contemporary model from Geschwind • New Neurobiology • Much better brain scan resolution • Integrated with cognitive psychology and linguistics Reading Skills Are Difficult to Acquire and Frequently Impaired Dyslexia—a reading disorder attributed to brain impairment Acquired dyslexia (alexia) can occur in adults after injury to the left hemisphere. Deep dyslexia is an acquired dylexia where patients read a word as another with a related meaning. In surface dyslexia, another acquired dylexia, the patient is restricted to the details and sounds of letters. Surface dyslexics find it difficult to recognize words in which the letter-to-sound rules are irregular. Surface dyslexia doesn’t occur in native speakers of languages that are perfectly phonetic (such as Italian). Types of Dyslexia • Developmental – Primary if from genetic abnormalities • Some genes related to brain development – Secondary if from abnormal prenatal through childhood development, including neglect. • Acquired (alexia) if caused by brain trauma – Deep problems with whole word recognition related in meaning, cow for horse – Surface difficulty with words that have irregular letter-to-sound rules Developmental Dyslexia • Not from low intelligence • Not a visual problem such as letter reversal • “an unexpected difficulty learning to read despite intelligence, motivation and education.” – Dyslexic children takes longer to learn how to talk. – While the language area of the brain is slower to develop, motor control skills come easier. – Dyslexics tend to learn how to walk earlier than other children. – Dyslexics have the higher rate of depression and suicide – Are less likely to finish high school or college. Developmental Dyslexia • Disorganized circuits – Mostly in the temporal lobes – Some amount in frontal cortex • Genetic predisposition related to neuronal migration early in development which produces – micropolygyria – ectopias – dysplasias • Processing deficits appear as early as 6 months • Difficulties processing consonant duration • Disorganized cortical connections – Disrupts flow of information to the inferior temporal region Reading Skills Are Difficult to Acquire and Frequently Impaired Developmental dyslexia occurs in 5% of children who have trouble learning to read. Brains of dyslexics show unusual arrangements of cortical cells. Micropolygyria—small regions of excessive number of gyri or cortical foldings Ectopias—clusters of extra cells Neural Disorganization in Dyslexia Developmental Dyslexia Treatment • Treated through education, and the sooner intervention begins, the better. – Learn to recognize the smallest sounds that make up words (phonemes) – Understand that letters and strings of letters represent these sounds • An increase in left-temporo-parietal and left inferior frontal activity after training • Also increased activity in right side frontal, temporal and anterior cingulate gyrus • Magnitude of increased activation in left temporo-parietal cortex correlated to improvement in oral language and improved reading