Prepared by Jeffrey W. Grimm Western Washington University PowerPoint Presentation for Biopsychology, 9th Edition by John P.J. Pinel Prepared by Jeffrey W. Grimm Western Washington University This multimedia product and its contents are protected under copyright law. The following are prohibited by law: any public performance or display, including transmission of any image over a network; preparation of any derivative work, including the extraction, in whole or in part, of any images; any rental, lease, or lending of the program. COPYRIGHT © 2014 PEARSON EDUCATION, INC. ALL RIGHTS RESERVED.

The Left Brain and the Right Brain Chapter 16 Lateralization, Language, and the Split Brain The Left Brain and the Right Brain Copyright © 2014 Pearson Education, Inc. All rights reserved.

Cerebral Lateralization of Function There are major differences between the functions of the left and right cerebral hemispheres. Cerebral commissures connect the two halves of the brain. Studies of split-brain patients have been instrumental in developing our understanding of what happens when these connections are severed. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Copyright © 2014 Pearson Education, Inc. Discovery of the Specific Contributions of Left-Hemisphere Damage to Aphasia and Apraxia Aphasia: deficit in language comprehension or production due to brain damage, usually on the left Broca’s area: left inferior prefrontal cortex; damage leads to expressive aphasia Apraxia: difficulty performing movements when asked to do so out of context; also a consequence of damage on the left Copyright © 2014 Pearson Education, Inc. All rights reserved.

Cerebral Lateralization of Function (Con’t) Aphasia and apraxia are associated with damage to left hemisphere. Language and voluntary movement seem to be controlled by one half of the brain, usually the left. This suggests that one hemisphere is dominant, controlling these functions. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Tests of Cerebral Lateralization Determining Which Hemisphere Is Dominant Sodium amytal test Anesthetize one hemisphere and check for language function Functional brain imaging fMRI or PET used to see which half is active when performing a language test Copyright © 2014 Pearson Education, Inc. All rights reserved.

Sex Differences in Brain Lateralization Women may use both hemispheres more often for language tasks than men do; women may be less lateralized. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Copyright © 2014 Pearson Education, Inc. The Split Brain Corpus callosum: largest cerebral commissure Transfers learned information from one hemisphere to the other When cut, each hemisphere functions independently Copyright © 2014 Pearson Education, Inc. All rights reserved.

Groundbreaking Experiment of Myers and Sperry Studied Split-Brain Cats Transected the corpus callosum and optic chiasm so that visual information could not cross to the contralateral hemisphere Copyright © 2014 Pearson Education, Inc. All rights reserved.

Split-Brain Cats (Con’t) Each hemisphere can learn independently. Split-brain cats with one eye patched: Learn task as well as controls No memory or savings demonstrated when the patch was transferred to other eye In intact cats, or those with an intact corpus callosum or optic chiasm, learning transfers between hemispheres. There have been similar findings with split-brain monkeys. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Commissurotomy in Human Epileptics Commissurotomy limits convulsive activity. Many of those who undergo the procedure never have another major convulsion. Sperry and Gazzaniga Developed procedures to test split-brain patients Split-brain humans differ from split-brain animals in that the two hemispheres of the human brain have very different abilities—most left hemispheres are capable of speech, while the right hemispheres are not. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Copyright © 2014 Pearson Education, Inc. Evidence that the Hemispheres of Split-Brain Patients Can Function Independently The left hemisphere can tell what it has seen; the right hemisphere can only show it. Present a picture to the right visual field (left brain). The left hemisphere can tell you what it was. The right hand can show you; the left hand can’t. Present a picture to the left visual field (right brain). Subjects will report that they do not know what it was. The left hand can show you what it was; the right can’t. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Dual Mental Functioning and Conflict in Split-Brain Patients In split-brain patients, the left hemisphere is usually dominant in most everyday activities. For some, the right is dominant, and this can create conflict between hemispheres. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Differences between the Left and Right Hemispheres For many functions there are no substantial differences, between hemispheres. Key point: Lateralization of function is statistical rather than absolute. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Examples of Cerebral Lateralization of Function Left hemisphere: an “interpreter” Right hemisphere superiority: Spatial ability Emotion Musical ability Some memory tasks Copyright © 2014 Pearson Education, Inc. All rights reserved.

Copyright © 2014 Pearson Education, Inc. Table 16.1 Abilities that Display Cerebral Lateralization of Function Copyright © 2014 Pearson Education, Inc. All rights reserved.

Copyright © 2014 Pearson Education, Inc. What is Lateralized: Broad Clusters of Abilities or Individual Cognitive Processes? Broad categories are not lateralized; individual tasks may be. It is more useful to consider lateralization of constituent cognitive processes: individual cognitive elements. E.g., two spatial tasks: the left hemisphere is better at judging above or below; the right is better at determining how close two things are to each other. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Anatomical Brain Asymmetries Frontal Operculum (Broca’s Area) Near face area of primary motor cortex Language production Planum Temporale (Wernicke’s Area) Temporal lobe, posterior lateral fissure Language comprehension Primary Auditory Cortex (Heschl’s Gyrus) Copyright © 2014 Pearson Education, Inc. All rights reserved.

Theories of the Evolution of Cerebral Asymmetry All theories propose that it’s better to have brain areas that have similar functions in the same hemisphere: analytic-synthetic theory. Two modes of thinking, analytic (left) and synthetic (right) Vague and essentially untestable “The darling of pop psychology” Copyright © 2014 Pearson Education, Inc. All rights reserved.

Theories of the Evolution of Cerebral Asymmetry (Con’t) Motor Theory Left controls fine movements; speech is just a category of fine movement. Left damage may produce speech and motor deficits. Linguistic Theory The primary role of the left hemisphere is language. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Historical Antecedents of the Wernicke-Geschwind Model Broca’s area: speech production Damage leads to expressive aphasia. Normal comprehension; speech is meaningful, but awkward. Wernicke’s area: speech comprehension Damage causes receptive aphasia. Poor comprehension; speech sounds normal, but has no meaning (“word salad”). Copyright © 2014 Pearson Education, Inc. All rights reserved.

Historical Antecedents of the Wernicke-Geschwind Model (Con’t) The arcuate fasciculus connects Broca’s and Wernicke’s areas. Damage to the arcuate fasciculus causes conduction aphasia (inability to repeat words just heard). Comprehension and speech are normal. Left angular gyrus: posterior to Wernicke’s area Damage causes alexia (inability to read) and agraphia (inability to write). Copyright © 2014 Pearson Education, Inc. All rights reserved.

Copyright © 2014 Pearson Education, Inc. FIGURE 16.10 The seven components of the Wernicke-Geschwind model. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Effects of Cortical Damage on Language Abilities No aphasic patients have damage restricted to Broca’s or Wernicke’s areas. Aphasics almost always have damage to subcortical white matter. Large anterior lesions are most likely to produce expressive symptoms. Large posterior lesions are most likely to produce receptive symptoms. Global aphasia is usually related to massive lesions of several regions. Aphasics sometimes have damage that does not encroach on Wernicke-Geschwind areas. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Functional Brain Imaging and Localization of Language Bevalier’s fMRI study of reading sought to establish cortical involvement in reading. Reading Sentences versus Control Periods (Strings of Consonants) Areas of activity were tiny and spread out. Active areas varied between subjects and trials. Activity was widespread. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Cognitive Neuroscience of Dyslexia Dyslexia: reading difficulties not due to some other deficit (e.g., vision, intelligence) Developmental dyslexia becomes apparent when the affected person is learning to read. Heritability estimate = 50 percent More common in boys than in girls Acquired Dyslexia Due to brain damage Relatively rare Copyright © 2014 Pearson Education, Inc. All rights reserved.

Developmental Dyslexia: Causes and Neural Mechanisms Brain differences have been identified, but none seem to play a role in the disorder. There are multiple types of developmental dyslexia—perhaps there are multiple causes. Perhaps dyslexia is a deficit of phonological processing rather than of sensorimotor processing. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Developmental Dyslexia (Con’t) Various subtle visual, auditory, and motor deficits are commonly seen. There is a genetic component—yet the disorder is also influenced by culture. More English speakers have reading deficits than do Italian speakers, perhaps because sound-symbol correspondence in English is more complex than it is in Italian. Copyright © 2014 Pearson Education, Inc. All rights reserved.

Cognitive Neuroscience of Deep and Surface Dyslexia Two Procedures for Reading Aloud Lexical: using stored information about words Phonetic: sounding out Surface dyslexia: lexical procedure lost; can’t recognize words Deep dyslexia: phonetic procedure lost; can’t sound out unfamiliar words Copyright © 2014 Pearson Education, Inc. All rights reserved.

Cognitive Neuroscience of Deep and Surface Dyslexia (Con’t) Surface dyslexia: loss of visual recognition of words (cannot “look and say”) Deep (or phonological) dyslexia: loss of ability to “sound out” unfamiliar words or nonwords Different error patterns are seen from those with surface versus deep dyslexia. Surface: “quail” for “quill” Deep: “hen” for “chicken” Copyright © 2014 Pearson Education, Inc. All rights reserved.

Cognitive Neuroscience of Deep and Surface Dyslexia (Con’t) Deep dyslexia: extensive damage to left-hemisphere language areas How is it that lexical abilities are spared? Lexical abilities may be housed in left language areas that are spared. Lexical abilities may be mediated by the right hemisphere. Evidence for both exists. Copyright © 2014 Pearson Education, Inc. All rights reserved.