Chapter 13 Lateralization Language Outline Lateralization of Function Language Communication Disorders Lateralization of Function Localization of function in one or the other hemisphere Hemispherectomy Rasmussen s Syndrome produces seizure in only one hemisphere Motor control modestly impaired Language development mostly unaffected 10 point increase in IQ Recovery of function correlates with age of surgery The Split Brain Pathways connecting two hemispheres severed in order to control seizures Temporal Lobes The Split Brain Pathways connecting two hemispheres severed in order to control seizures No change in personality intelligence or speech Two separate minds Alien hand syndrome The Split Brain Language capacities between two hemispheres The Split Brain Language capacities between two hemispheres The Split Brain The Interpreter one hemisphere usually left tries to make sense of actions Right hemisphere may point to object but left hemisphere does not know why Interpreter attempts to generate a reasonable explanation The Split Brain Two hemispheres process different types of information Left hemisphere logical sequential verbal Right hemisphere emotional intuitive spatial relations Patients brains may not be representative Development of Lateralization Lateralization not unique to humans May allow organisms to simultaneously attend to different aspects of environment Development of Lateralization Lateralization Role of prenatal androgens Males higher proportion of left handers Congenital adrenal hyperplasia CAH fetus adrenal glands release elevated levels of androgens Females exposed to twice normal level no difference in handedness or language laterality Males exposed to slightly elevated levels higher proportion left handed but no difference in language Development of Lateralization Lateralization Other factors Genes responsible for connectivity between two hemispheres activated at 3 5 months Differential gene expression might result in different wiring patterns leading to structural and functional differences later in life Hemispheric Asymmetry Handedness Language 10 left handed 70 localize language to left hemisphere 15 localize to right hemisphere 15 localize to both hemispheres 90 right handed 95 localize language to left hemisphere 4 localize to right hemisphere 1 localize to both hemispheres Hemispheric Asymmetry Handedness Language Dioula tribe 3 4 left handed Yanomamo tribe 22 6 left handed Hemispheric Asymmetry Dichotic Listening different sounds presented simultaneously to both ears Right handers typically show right ear left hemisphere advantage Hemispheric Asymmetry Prosody use of intonation and stress in language to convey emotional tone and meaning Left ear right hemisphere advantage in responding to emotional words Orbitofrontal cortices in both hemispheres respond to conscious evaluation of emotional tone Hemispheric Asymmetry Musical ability Imaging results suggest overlap between language and music rTMS suggests right hemispheric activity only Hemispheric Asymmetry Musical ability Perfect pitch Planum temporale brain region near auditory cortex Larger in left hemisphere Twice as large in musicians with perfect pitch Hemispheric Asymmetry Gender differences 3 7 times many boys than girls diagnosed with language disorder Girls begin speaking at younger age have larger vocabulary and better reading skills Large meta analysis found gender difference in lateralization of handedness but not language
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