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Language Lateralization Brain
- 1. 11: Language and Lateralization Cognitive Neuroscience David Eagleman Jonathan Downar
- 2. Chapter Outline Speech, Language, and Communcation Aphasia: The Loss of Language A Language Network Lateralization: The Two Hemispheres Are Not Identical Development and Language 2
- 3. Speech, Language, and Communication Speech is the sound output meant to convey meaning. Language is the ability to translate our ideas into signals for another person. Communication is the ability to convey meaning to another person, regardless of the media. 3
- 5. Aphasia: The Loss of Language Broca’s Aphasia Wernicke’s Aphasia 5
- 6. Broca’s Aphasia Dysphonia and dysarthria are injuries to the vocal muscles. Aphasias result from damage to particular areas of the brain. There are more than 10 different named aphasias. 6
- 7. Broca’s Aphasia This is caused by lesions to the left lateral frontal lobe. This is known as an expressive aphasia, because patients have difficulty expressing language. Writing is equally impaired. 7
- 9. Wernicke’s Aphasia This involves damage to the left superior temporal gyrus. This is known as a receptive aphasia, because patients have difficulty comprehending language. The speech sounds fluent, but is nonsensical and contains many filler words. 9
- 11. A Language Network The Larger Picture of Language-Specific Regions Dyslexia Stuttering 11
- 12. The Larger Picture of Language- Specific Regions The Wernicke-Geschwind model describes the language network Major components include Broca’s area, Wernicke’s area, and the arcuate fasciculus, which connects them. This model is an over-simplification of the language network. 12
- 13. The Larger Picture of Language- Specific Regions 13
- 14. The Larger Picture of Language- Specific Regions There is an elaborate and extensive network of language areas outside the Wernicke-Geschwind model. Nouns and verbs are located in different parts of the brain. Areas in the left frontal lobe and the left temporal-parietal area are activated only during language tasks. 14
- 15. The Larger Picture of Language- Specific Regions 15
- 16. The Larger Picture of Language- Specific Regions 16
- 17. The Larger Picture of Language- Specific Regions 17
- 18. Dyslexia Dyslexia is a developmental disorder in which subjects have difficulty reading. Dyslexia is not due to a sensory problem or intellectual impairment. In surface dyslexia, individuals have difficulty with the appearance of language. In deep dyslexia, individuals have difficulty with the sound structure of language. 18
- 19. Dyslexia Individuals with dyslexia have problems with the left hemisphere language areas. There is less activity in the Wernicke’s area, compared with fluent readers. There is compensatory activity in the left anterior language areas and the right hemisphere. 19
- 20. Dyslexia 20
- 21. Stuttering Individuals who stutter have increased activity in Broca’s area, the supplementary motor area, the insula and the cerebellum. They show decreased activity in the auditory regions of the temporal lobe. 21
- 22. Lateralization: The Two Hemispheres Are Not Identical Tests for Dominance Apraxia Hemispheric Differences Two Brains in One? The Case of the Split- Brain Patients Thinking about Cerebral Asymmetry 22
- 23. Tests for Dominance The Wada test is used to establish hemispheric dominance for language before surgery. A barbiturate is injected into one hemisphere to interrupt speech. fMRI-based tests are more precise and less invasive. 23
- 25. Apraxia The left hemisphere is dominant for language in 92% of right handed individuals and 69% of left handed individuals. The left hemisphere is also dominant for fine motor control. Apraxia is difficulty performing fine movements out of context. 25
- 26. Apraxia 26
- 27. Hemispheric Differences The right hemisphere has greater spatial abilities than the left hemisphere. It is also better at perceiving and understanding emotion. Language is already lateralized for babies at two months of age. The planum temporale is larger in the left hemisphere and may be associated with language fluency. 27
- 29. Two Brains in One? The Case of the Split-Brain Patients The two hemispheres are separate but interconnected. The corpus callosum is the major connection between the hemispheres. Sometimes, this connection is cut to prevent the spread of seizures. Split-brain patients essentially have two independent hemispheres. 29
- 30. Two Brains in One? The Case of the Split-Brain Patients 30
- 31. Two Brains in One? The Case of the Split-Brain Patients Split-brain patients can perform two different tasks simultaneously. They can verbally describe a stimulus presented to the right visual field (which projects to the left hemisphere). They cannot describe a stimulus presented to the left visual field. 31
- 32. Two Brains in One? The Case of the Split-Brain Patients 32
- 33. Thinking about Cerebral Asymmetry It may be more efficient to localize linguistic functions in one hemisphere. According to the analytic-synthetic theory, the left hemisphere is better at analysis and the right is better at synthesis. According to the motor theory, the left hemisphere is better at fine motor control, of which speech is one example. 33
- 34. Development of Language Learning Language from Experience Innate Language Tendencies Socially and Emotionally Directed Learning 34
- 35. Learning Language from Experience Language is instinctively learned by babies. Children learn language by statistical learning, or observing the patterns in what they hear. The slower articulation of parentese makes it easier for a baby to analyze language. 35
- 38. Learning Language from Experience By nine months of age, babies prefer the sounds of their own language. Babies lose the ability to hear sounds that are not part of their native language by about one year. 38
- 40. Innate Language Tendencies One theory, universal grammar, is that we are born with the predisposition to learn the grammar of a language. Patterns of language development are similar across all languages. Children do not hear enough examples of language to explain this innate learning, supporting a universal grammar. 40
- 41. Socially and Emotionally Directed Learning Social interaction is important for learning language. In a study of Mandarin language learners, infants who interacted with the teacher learned more than infants that listened to recordings of the lessons. There may be some language abilities in other species, but that is not agreed upon. 41
- 42. Socially and Emotionally Directed Learning 42
Editor's Notes
- FIGURE 11.2 Speech involves the production and transmission of sound waves.
- FIGURE 11.3 Broca’s area. (a) Damage to this region leads to a diminished ability to express language. Such damage usually results from blockage or hemorrhage of the middle cerebral artery, tumors, or traumatic brain injury. Note the proximity of Broca’s area to the premotor cortex. The preserved brains of Broca’s patients, (b) Leborgne (upper) and Lelong (lower).
- FIGURE 11.4 Wernicke’s area. Damage to this region leads to receptive aphasias. Wernicke’s aphasias result most commonly from damage to the posterior branches of the middle cerebral artery, whether by blockage of the artery or by hemorrhage, and sometimes from tumors or from traumatic brain injury to the region.
- FIGURE 11.6 Wernicke–Geschwind model. This circuit diagrams the path of language in the brain. (A) Auditory inputs (spoken words) move from the auditory cortex to Wernicke’s area. (B) Visual inputs (written words) move from the occipital cortex through the angular gyrus to Wernicke’s area. (C) After an analysis of the input, language information moves to Broca’s area via the arcuate fasciculus. (D) Broca’s area is necessary to create the production of a response to the input. Finally, Broca’s area outputs the articulation of a response through the motor cortex, which then passes the signal to the muscles needed to produce the response (e.g., speech sounds, writing, or sign language).
- FIGURE 11.8 Different brain areas are activated when producing nouns (red areas) than when producing verbs (green areas).
- FIGURE 11.9 Areas of the brain that are specifically involved in language functions. (a) The language-related activity in six regions of the brain. (b) Activity in these same areas during nonlinguistic tasks. (c) The difference between these two conditions (activity during linguistic tasks minus activity during nonlinguistic tasks), highlighting areas important for linguistic tasks.
- FIGURE 11.10 Linguistic processing is mapped out onto different brain areas. (a) The parts of the brain specialized for grammar processing. (b) The areas involved in sentence comprehension (green) and areas involved in syntactic processing (purple). Adapted from Sakai et al. (2005).
- FIGURE 11.11 Activity in the language-related areas in dyslexia. During language tasks, individuals with dyslexia have less activity in the more posterior language-related areas and greater activity in the anterior areas.
- FIGURE 11.12 The Wada test. In the Wada test, sodium amobarbital is injected into the carotid artery to anesthetize half of the brain. This helps clinicians find out whether language functions are on the right half or the left half of a person’s brain.
- FIGURE 11.13 A physical exam for apraxia. A person with apraxia is unable to mime requested actions involving fine motor control out of context, such as blowing out a match, hammering a nail, or threading a needle.
- FIGURE 11.14 Hemispheric asymmetry in the planum temporale. (a) The planum temporale is located on the temporal lobe. (b) It is generally larger in the left hemisphere than in the right in fluent readers. (c) This asymmetry is absent or reversed in individuals with dyslexia.
- FIGURE 11.15 The corpus callosum.
- FIGURE 11.16 Behavioral studies of split-brain patients. (a) A compound word is presented briefly, so that what is presented on the left side of the screen only goes to the right side of the brain and what is presented on the right side of the screen only goes to the left side of the brain. The patient can say what was on the right side of the screen, but can identify the word on the left side of the screen only by touch with the left hand. (b) Because the two hemispheres of the brain have been disconnected from each other, split-brain patients can easily perform two separate actions with their left and right hands.
- FIGURE 11.17 A spectrogram of spoken English. (a) A recording of the spoken phrase “We owe you.” (b) The same phrase spoken with clear pauses between the words: “We,” “owe,” “you.” Note in (a) that there are no pauses in the recording, although we hear them between the words.
- FIGURE 11.18 Building boundaries in phoneme space. Through exposure to spoken language, infant brains divide the space of possible phonemes into categories. This example shows the differences in vowel planes for (a) American and (b) Australian accents of English. The F1 frequency measurement (vertical axis) relates to how open the mouth is, and the F2 frequency measurement (horizontal axis) relates to whether the tongue is constricted toward the front or the back of the mouth.
- FIGURE 11.19 Developmental milestones for language. (a) The ages at which children typically are able to make sounds or speak. (b) A similar timeline for when children typically comprehend language.
- FIGURE 11.21 Effects of live interaction in language learning. American infants were tested on Mandarin Chinese speech discrimination. When exposed to live interaction with actual speakers of Chinese, there was significantly more learning than from exposure to American English. In the absence of a live person (audiovisual or audio only), there was no learning.