BRAIN BRAIN LATERALIZATIONLATERALIZATIONLANGUAGE AND LANGUAGE AND

COGNITIONCOGNITION

CEREBRAL LATERALIZATIONCEREBRAL LATERALIZATION Significant Events in HistorySignificant Events in History

• Marc Dax (1836)Marc Dax (1836) Dax was the first to report left hemisphere Dax was the first to report left hemisphere

involvement in speech disorders caused by involvement in speech disorders caused by brain damage.brain damage.

• Paul Broca (1860’s)Paul Broca (1860’s) Unaware of Dax’s work, Broca made key Unaware of Dax’s work, Broca made key

discoveries regarding left hemisphere discoveries regarding left hemisphere involvement in aphasia.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 Apraxia is almost always caused by left

hemisphere damage.hemisphere damage.

CEREBRAL LATERALIZATIONCEREBRAL LATERALIZATION Assessments of Lateralization Assessments of Lateralization

• Sodium Amytal TestSodium Amytal Test• Dichotic Listening Test Dichotic Listening Test • Functional Brain ImagingFunctional Brain Imaging

CEREBRAL LATERALIZATIONCEREBRAL LATERALIZATION Speech lateralization and handednessSpeech lateralization and handedness

• The left hemisphere is dominant for speech in The left hemisphere is dominant for speech in majority, both right- and left-handed, although majority, both right- and left-handed, although greater variability among left-handed individuals.greater variability among left-handed individuals.

Neurological studies of aphasics (Russell & Esper, Neurological studies of aphasics (Russell & Esper, 1961).1961).

• Right handed aphasics: 60% left, 2% right hemisphere Right handed aphasics: 60% left, 2% right hemisphere damagedamage

• Left handed aphasics: 30% left, 24% right hemisphere Left handed aphasics: 30% left, 24% right hemisphere damagedamage

Results of Sodium amytal tests (Milner, 1974).Results of Sodium amytal tests (Milner, 1974).Left-hemisphere dominance for speech in: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 30% of left-handed or ambidextrous individuals with early

left hemisphere damageleft hemisphere damage

CEREBRAL LATERALIZATIONCEREBRAL LATERALIZATION

Sex Differences and LateralizationSex Differences and Lateralization• Some evidence suggests that the male Some evidence suggests that the male

brain is more lateralized than female brain.brain is more lateralized than female brain.• e.g., McGlone’s (1977, 1980) studies of e.g., McGlone’s (1977, 1980) studies of

unilateral stroke victims and WAIS unilateral stroke victims and WAIS subscore testssubscore tests

• Some fMRI studies show that females tend Some fMRI studies show that females tend to use both hemispheres in language-to use both hemispheres in language-related tasks more so than males.related tasks more so than males.

SPLIT-BRAIN STUDIESSPLIT-BRAIN STUDIES Meyers’ and Sperry’s work in catsMeyers’ and Sperry’s work in cats Split-Brain PatientsSplit-Brain Patients

• Commisurotomy to reduce seizure Commisurotomy to reduce seizure spreading.spreading.

Tests involving verbal identification of Tests involving verbal identification of stimuli presented to the left or right stimuli presented to the left or right hemisphere.hemisphere.

Tests involving spatial stimuli presented to L Tests involving spatial stimuli presented to L or R hemisphere.or R hemisphere.

Myers and Sperry (1953)Myers and Sperry (1953)

Testing Split-Brain PatientsTesting Split-Brain Patients

HEMISPHERIC SPECIALIZATIONSHEMISPHERIC SPECIALIZATIONS

Examples of LateralizationExamples of Lateralization• Left Hemisphere SpecializationsLeft Hemisphere Specializations

LanguageLanguage Controlling ipsilateral movementControlling ipsilateral movement

• Right Hemisphere SpecializationsRight Hemisphere Specializations Spatial abilitySpatial ability EmotionEmotion Musical abilityMusical ability

• See table 16.1 in Pinel for more examplesSee table 16.1 in Pinel for more examples

NEUROANATOMICAL ASSYMETRYNEUROANATOMICAL ASSYMETRY Planum TemporalePlanum Temporale

• Larger in left hemisphere in most individualsLarger in left hemisphere in most individuals Geschwind and Levitsky (1968) studyGeschwind and Levitsky (1968) study Witelson (1983) studyWitelson (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 pitchLeft planum temporale and perfect pitch

APHASIAAPHASIA

Definition: Acquired disorders of Definition: Acquired disorders of language secondary to brain damagelanguage secondary to brain damage

Common SubtypesCommon Subtypes• Broca’s aphasiaBroca’s aphasia• Wernicke’s aphasiaWernicke’s aphasia• Global AphasiaGlobal Aphasia• Conduction AphasiaConduction Aphasia

LANGUAGE AREASLANGUAGE AREAS

BROCA’S APHASIABROCA’S APHASIA

Characteristic symptomsCharacteristic 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 damageRegion of brain damage• left inferior frontal cortex, 3rd frontal gyrus, left inferior frontal cortex, 3rd frontal gyrus,

anterior to face region of motor cortex anterior to face region of motor cortex (Broca’s area)(Broca’s area)

WERNICKE’S APHASIAWERNICKE’S APHASIA Characteristic symptomsCharacteristic symptoms

• poor comprehension of spoken and written poor comprehension of spoken and written languagelanguage

• fluent and spontaneous speech, but fluent and spontaneous speech, but incoherentincoherent

• paraphasia (sound and word substitutions)paraphasia (sound and word substitutions)• alexia (reading impairment)alexia (reading impairment)

Region of brain damageRegion of brain damage• left superior temporal gyrus (Wernicke’s left superior temporal gyrus (Wernicke’s

area)area)

GLOBAL APHASIAGLOBAL APHASIA CharacteristicsCharacteristics

• Total loss of comprehension and Total loss of comprehension and expressive abilities, involving both expressive abilities, involving both spoken and written language.spoken and written language.

• Some automatic speech, such as Some automatic speech, such as emotional exclamations retainedemotional exclamations retained

Damage is extensiveDamage is extensive• involves both B. and W. areas, large involves both B. and W. areas, large

portions of frontal, temporal and portions of frontal, temporal and parietal cortex.parietal cortex.

CONDUCTION APHASIACONDUCTION APHASIA CharacteristicsCharacteristics

• fluent speech, comprehension only slightly fluent speech, comprehension only slightly impairedimpaired

• repetition primarily impaired (esp. novel or repetition primarily impaired (esp. novel or nonwords, or sentences)nonwords, or sentences)

Brain regions damagedBrain regions damaged• arcuate fasciculus arcuate fasciculus (connection between B and W (connection between B and W

area)area)

• or primary auditory cortex or primary auditory cortex

APHASIAS: SUMMARYAPHASIAS: SUMMARY

APHASIAS: SUMMARYAPHASIAS: SUMMARY

WERNICKE-GESCHWIND MODELWERNICKE-GESCHWIND MODEL

Connectionist Model Connectionist Model for the anatomical for the anatomical analysis of aphasiasanalysis of aphasias

DYSLEXIADYSLEXIA

Developmental DyslexiasDevelopmental Dyslexias• Some controversy in categorizing this Some controversy in categorizing this

disorderdisorder• Sensory-processing problem? Sensory-processing problem? • Memory disorder?Memory disorder?

Acquired DyslexiasAcquired Dyslexias• surface dyslexia (whole word reading surface dyslexia (whole word reading

impaired)impaired)• deep dyslexia (phonological dyslexia)deep dyslexia (phonological dyslexia)

NEURAL ABNORMALITIES IN DYSLEXIANEURAL ABNORMALITIES IN DYSLEXIA

Anomalies in cortical cell arrangementAnomalies in cortical cell arrangement• Ectopias: unusual groupings of cells in Ectopias: unusual groupings of cells in

outer layersouter layers• Micropolygyria: excessive cortical foldingMicropolygyria: excessive cortical folding• Disoriented cellsDisoriented cells

These abnormalities probably occur These abnormalities probably occur during neural migration during fetal during neural migration during fetal developmentdevelopment

BRAIN IMAGING DYSLEXIABRAIN IMAGING DYSLEXIA fMRI studies show different patterns fMRI studies show different patterns

of brain activation in dyslexics and of brain activation in dyslexics and nondyslexics.nondyslexics.

Dyslexic subjects:Dyslexic subjects:• showed less activation in posterior showed less activation in posterior

regions (e.g. Wernicke’s area) and regions (e.g. Wernicke’s area) and overactivity in anterior regions overactivity in anterior regions compared to nondyslexics.compared to nondyslexics.

• showed less activation of visual cortex showed less activation of visual cortex in response to written words.in response to written words.