Pinel basics ch14

Chapter 14 Lateralization, Language, and the Split Brain The Left Brain and the Right Brain of Language 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.

Lateralization of Function Major differences between the function of the left and right cerebral hemispheres Cerebral commissures connect the 2 halves of the brain Split-brain patients – what happens when the connections are severed?

Cerebral Lateralization of Function 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 so out of context – also a consequence of damage on the left

Cerebral Lateralization of Function Aphasia and apraxia – associated with damage to left hemisphere Language and voluntary movement seem to be controlled by one half of the brain – usually the left Suggests that one hemisphere is dominant, controlling these functions

Tests of Cerebral Lateralization Determining which hemisphere is dominant Sodium amytal test Anesthetize one and check for language function Dichotic listening Report more digits heard by the dominant half Functional brain imaging f MRI or PET used to see which half is active when doing a language test

Speech Laterality, Handedness, and Sex Dextrals: right-handers Sinestrals: left-handers Left-hemisphere dominant in almost all dextrals and most sinestrals Females may use both hemispheres more often for language tasks than men do – less lateralized

The Split Brain Corpus callosum – largest cerebral commissure Transfers learned information from one hemisphere to the other When cut, each hemisphere functions independently Studying split-brain cats – transect corpus callosum and optic chiasm so that visual information can’t cross

Split-Brain Cats 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 Intact cats or those with an intact corpus callosum or optic chiasm – learning transfers between hemispheres Similar findings with split-brain monkeys

Commissurotomy in Human Epileptics Commissurotomy limits convulsive activity many never have another major convulsion Sperry & Gazzaniga developed procedures to test split-brain patients Differ from split-brain animals in that the 2 hemispheres have very different abilities – most left hemispheres are capable of speech, while the right aren’t

Hemispheres of Split-Brain Patients Function Independently Left hemisphere can tell what it has seen, right hemisphere can show it. Studies of split-brain patients: Present a picture to the right visual field (left brain) Left hemisphere can tell you what it was Right hand can show you, left hand can’t Present a picture to the left visual field (right brain) Subject will report that they do not know what it was Left hand can show you what it was, right can’t

Cross-Cuing Allows the two hemispheres of a split-brain subject to communicate with each other indirectly . Gazzaniga’s color test showed that neurological patients make use of various strategies, including interpreting their own physical cues, to correct their answers.

Learning 2 Things at Once Each hemisphere of a split-brain can learn independently and simultaneously Presented with 2 different visual stimuli Helping-hand phenomenon – the hand that “knows” may correct the other Chimeric figures task

Dual Mental Functioning and Conflict in Split-Brain Patients In most split-brain patients, the left hemisphere seems to control most activities. In a few patients, the right hemisphere takes a more active role in controlling behavior, which can create conflicts between the left and right hemispheres. Peter, the Split-Brain Patient

Differences Between the Hemispheres For many functions the hemispheres do not differ and where there are differences, these tend to be minimal Lateralization of function is statistical, not absolute Right hemisphere has some language abilities

Examples of Lateralization of Function Right hemisphere superiority Spatial ability Emotion Musical ability Some memory tasks Left hemisphere – superior in controlling ipsilateral movement

Right hemisphere superiority Spatial ability Better at matching 3-D image with 2-D Emotion Better at perceiving facial expressions and mood Musical ability Better at perception of melodies Some memory tasks Nonverbal material Learning tasks where context doesn’t matter

What is Lateralized – Broad Clusters of Abilities or Individual Cognitive Processes? Broad categories are not lateralized – individual tasks may be Better to consider lateralization of constituent cognitive processes – individual cognitive elements Example – left is better at judging above or below, right at how close 2 things are

Anatomical Brain Asymmetries Planum temporale (Wernicke’s Area) Temporal lobe, posterior lateral fissure Language comprehension Heschl’s gyrus - primary auditory cortex Frontal operculum (Broca’s Area) Near face area of primary motor cortex Language production

Anatomical Brain Asymmetries Although asymmetries are seen in language related areas, these regions are not all larger in the left Left planum temporal – larger in 65% Heschl’s gyri – larger on the right 2 in the right, only 1 in left Frontal operculum – visible surface suggests right is larger, but there is greater volume on left

Theories of Cerebral Aysmmetry All propose that it’s better to have brain areas that do similar things be in the same hemisphere Analytic-synthetic theory 2 modes of thinking, analytic (left) and synthetic (right) Vague and essentially untestable “ the darling of pop psychology”

Theories of Cerebral Aysmmetry Motor theory Left controls fine movements – speech is just a category of movement Left damage may produce speech and motor deficits Linguistic theory Primary role of left is language

Evolution of Lateralization of Function Nonhuman primates tend to use their right hand for certain tasks Hand preference is under genetic influence in chimps Indicates tool use was not the major factor in the evolution of lateralization Lateralization of aspects of communcation and emotion also seen in other species

Antecedents of the Wernicke-Geschwind Model Language localization – intrahemispheric organization of language circuitry Broca’s area – production Damage > expressive aphasia Normal comprehension, speech is meaningful – but awkward Wernicke’s area – comprehension Damage > receptive aphasia Poor comprehension, speech sounds normal – but has no meaning – ‘word salad’

Antecedents of the Wernicke-Geschwind Model Arcuate fasciculus – connects Broca’s and Wernicke’s Damage > conduction aphasia Comprehension and speech normal Unable to repeat Left angular gyrus – posterior to Wernicke’s area Damage > alexia (inability to read) and agraphia (inability to write)

Evaluation of the Wernicke-Geschwind Model Can it predict the deficits produced by damage to various parts of the cortex? Surgery that destroys only Broca’s area has no lasting effects on speech Removal of much of Wernicke’s area does not have any lasting effects on speech Some argue that failure to support the model is due to pathology-related reorganization

Effects of Damage to Areas of Cortex on Language Abilities

Current Status of the Wernicke-Geschwind Model Empirical evidence supports 2 elements: Important roles played Broca’s and Wernicke’s – many aphasics have damage in these areas Anterior damage associated with expressive deficits and posterior with receptive No support for more specific predictions Damage limited to identified areas has little lasting effect on language Brain damage in other areas can produce aphasia Pure aphasias (expressive OR receptive) rare

Cognitive Neuroscience Approach to Language Language-related behaviors are mediated by activity in brain areas involved in the specific cognitive processes required for the behaviors. Brain areas involved in language have other functions. Brain areas involved in language are likely to be small, widely distributed, and specialized.

Functional Brain Imaging and Language f MRI and reading – Bavelier determines the extent of cortical involvement in reading Use a sensitive f MRI machine to record activity during reading of sentences Areas of activity were tiny and spread out. Active areas varied between subjects and trials. Activity was widespread.

Functional Brain Imaging and Language

f MRI and Reading More activity in the left hemisphere than in the right Activity extended well beyond what Wernicke-Geschwind predicted

Functional Brain Imaging and Language PET and naming Images of famous faces, animals, and tools Activity while judging image orientation subtracted from activity while naming – Left temporal lobe areas activated by naming varied with category Activity seen well beyond Wernicke’s Area

Cognitive Neuroscience Approach and Dyslexia Dyslexia – reading difficulties not due to some other deficit Developmental dyslexia – apparent when learning to read Acquired dyslexia – due to brain damage

Developmental Dyslexia Brain differences identified, but none seems to play a role in the disorder Multiple types of developmental dyslexia – possibly multiple causes Differences could be due to reading problems, not the cause of difficulties

Developmental Dyslexia Various subtle visual, auditory, and motor deficits are commonly seen Are these deficits the primary problem – do they cause the dyslexia? Genetic component – yet the disorder is also influenced by culture More English speakers are dyslexic than Italian – due to English being more complex

Acquired Dyslexia - Deep and Surface 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

Acquired Dyslexia - Deep and Surface Where’s the damage? 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

Pinel basics ch14

Pinel basics ch14

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Pinel basics ch14