BRAIN LATERALIZATION LANGUAGE AND COGNITION

CEREBRAL LATERALIZATION  Significant Events in History Marc Dax (1836)Marc Dax (1836)  Dax was the first to report left hemisphere involvement in speech disorders caused by brain damage. Paul Broca (1860’s)Paul Broca (1860’s)  Unaware of Dax’s work, Broca made key discoveries regarding left hemisphere involvement in aphasia. Broca’s area, Broca’s aphasiaBroca’s area, Broca’s aphasia Hugo-Karl Liepmann (1900’s)Hugo-Karl Liepmann (1900’s)  Apraxia is almost always caused by left hemisphere damage.

CEREBRAL LATERALIZATION  Assessments of Lateralization Sodium Amytal TestSodium Amytal Test Dichotic Listening Test Dichotic Listening Test  Functional Brain ImagingFunctional Brain Imaging

CEREBRAL LATERALIZATION  Speech lateralization and handedness The left hemisphere is dominant for speech in majority, both right- and left-handed, although greater variability among left-handed individuals.The left hemisphere is dominant for speech in majority, both right- and left-handed, although greater variability among left-handed individuals.  Neurological studies of aphasics (Russell & Esper, 1961). Right handed aphasics: 60% left, 2% right hemisphere damageRight handed aphasics: 60% left, 2% right hemisphere damage Left handed aphasics: 30% left, 24% right hemisphere damageLeft handed aphasics: 30% left, 24% right hemisphere damage  Results of Sodium amytal tests (Milner, 1974). Left-hemisphere dominance for speech in: 92% of right-handed individuals92% of right-handed individuals 69% of left-handed or ambidextrous individuals69% of left-handed or ambidextrous individuals 30% of left-handed or ambidextrous individuals with early left hemisphere damage30% of left-handed or ambidextrous individuals with early left hemisphere damage

CEREBRAL LATERALIZATION  Sex Differences and Lateralization Some evidence suggests that the male brain is more lateralized than female brain.Some evidence suggests that the male brain is more lateralized than female brain. e.g., McGlone’s (1977, 1980) studies of unilateral stroke victims and WAIS subscore testse.g., McGlone’s (1977, 1980) studies of unilateral stroke victims and WAIS subscore tests Some fMRI studies show that females tend to use both hemispheres in language- related tasks more so than males.Some fMRI studies show that females tend to use both hemispheres in language- related tasks more so than males.

SPLIT-BRAIN STUDIES  Meyers’ and Sperry’s work in cats  Split-Brain Patients Commisurotomy to reduce seizure spreading.Commisurotomy to reduce seizure spreading.  Tests involving verbal identification of stimuli presented to the left or right hemisphere.  Tests involving spatial stimuli presented to L or R hemisphere.

Myers and Sperry (1953)

Testing Split-Brain Patients

HEMISPHERIC SPECIALIZATIONS  Examples of Lateralization Left Hemisphere SpecializationsLeft Hemisphere Specializations  Language  Controlling ipsilateral movement Right Hemisphere SpecializationsRight Hemisphere Specializations  Spatial ability  Emotion  Musical ability See table 16.1 in Pinel for more examplesSee table 16.1 in Pinel for more examples

NEUROANATOMICAL ASSYMETRY  Planum Temporale Larger in left hemisphere in most individualsLarger in left hemisphere in most individuals  Geschwind and Levitsky (1968) study  Witelson (1983) study Asymmetry is present at infancyAsymmetry is present at infancy Asymmetry of planum temporale in chimps and other apesAsymmetry of planum temporale in chimps and other apes  Left planum temporale and perfect pitch

APHASIA  Definition: Acquired disorders of language secondary to brain damage  Common Subtypes Broca’s aphasiaBroca’s aphasia Wernicke’s aphasiaWernicke’s aphasia Global AphasiaGlobal Aphasia Conduction AphasiaConduction Aphasia

LANGUAGE AREAS

BROCA’S APHASIA  Characteristic symptoms labored and poorly articulated speechlabored and poorly articulated speech agrammatism (telegraphic speech)agrammatism (telegraphic speech) anomiaanomia agraphia (writing impairment)agraphia (writing impairment)  Region of brain damage left inferior frontal cortex, 3rd frontal gyrus, anterior to face region of motor cortex (Broca’s area)left inferior frontal cortex, 3rd frontal gyrus, anterior to face region of motor cortex (Broca’s area)

WERNICKE’S APHASIA  Characteristic symptoms poor comprehension of spoken and written languagepoor comprehension of spoken and written language fluent and spontaneous speech, but incoherentfluent and spontaneous speech, but incoherent paraphasia (sound and word substitutions)paraphasia (sound and word substitutions) alexia (reading impairment)alexia (reading impairment)  Region of brain damage left superior temporal gyrus (Wernicke’s area)left superior temporal gyrus (Wernicke’s area)

GLOBAL APHASIA  Characteristics Total loss of comprehension and expressive abilities, involving both spoken and written language.Total loss of comprehension and expressive abilities, involving both spoken and written language. Some automatic speech, such as emotional exclamations retainedSome automatic speech, such as emotional exclamations retained  Damage is extensive involves both B. and W. areas, large portions of frontal, temporal and parietal cortex.involves both B. and W. areas, large portions of frontal, temporal and parietal cortex.

CONDUCTION APHASIA  Characteristics fluent speech, comprehension only slightly impairedfluent speech, comprehension only slightly impaired repetition primarily impaired (esp. novel or nonwords, or sentences)repetition primarily impaired (esp. novel or nonwords, or sentences)  Brain regions damaged arcuate fasciculus (connection between B and W area)arcuate fasciculus (connection between B and W area) or primary auditory cortexor primary auditory cortex

APHASIAS: SUMMARY

WERNICKE-GESCHWIND MODEL Connectionist Model for the anatomical analysis of aphasias

DYSLEXIA  Developmental Dyslexias Some controversy in categorizing this disorderSome controversy in categorizing this disorder Sensory-processing problem?Sensory-processing problem? Memory disorder?Memory disorder?  Acquired Dyslexias surface dyslexia (whole word reading impaired)surface dyslexia (whole word reading impaired) deep dyslexia (phonological dyslexia)deep dyslexia (phonological dyslexia)

NEURAL ABNORMALITIES IN DYSLEXIA  Anomalies in cortical cell arrangement Ectopias: unusual groupings of cells in outer layersEctopias: unusual groupings of cells in outer layers Micropolygyria: excessive cortical foldingMicropolygyria: excessive cortical folding Disoriented cellsDisoriented cells  These abnormalities probably occur during neural migration during fetal development

BRAIN IMAGING DYSLEXIA  fMRI studies show different patterns of brain activation in dyslexics and nondyslexics.  Dyslexic subjects: showed less activation in posterior regions (e.g. Wernicke’s area) and overactivity in anterior regions compared to nondyslexics.showed less activation in posterior regions (e.g. Wernicke’s area) and overactivity in anterior regions compared to nondyslexics. showed less activation of visual cortex in response to written words.showed less activation of visual cortex in response to written words.