Chapter 14: Cognitive Functions

1. Chapter 14:Cognitive Functions

3. Lateralization of Function The left and right hemisphere exchange information primarily through a set of axons called the corpus callosum. Other areas that exchange information include: The anterior commissure. The hippocampal commissure. A few other small commissures. Information crosses to the other hemisphere with only a brief delay.

4. Figure 14.2: Two views of the corpus callosum. The corpus callosum is a large set of axons conveying information between the two hemispheres. (a) A sagittal section through the human brain. (b) A dissection (viewed from above) in which gray matter has been removed to expose the corpus callosum.Figure 14.2: Two views of the corpus callosum. The corpus callosum is a large set of axons conveying information between the two hemispheres. (a) A sagittal section through the human brain. (b) A dissection (viewed from above) in which gray matter has been removed to expose the corpus callosum.

5. Lateralization of Function The two hemispheres are not mirror images of each other. Division of labor between the two hemispheres is known as lateralization. In most humans the left side is specialized for language. The corpus callosum allows each hemisphere of the brain access to information from both sides.

6. Lateralization of Function Each hemisphere of the brain gets input from the opposite half of the visual world. The visual field is what is visible at any moment. Light from the right half of the visual field shines into the left half of both retinas. Light from the left visual field shines onto the right half of both retinas.

7. Lateralization of Function The left half of each retina connects to the left hemisphere. The right half of each retina connects to the right hemisphere. Half of the axons from each eye cross to the opposite side of the brain at the optic chiasm. The auditory system is arranged differently in that each ear sends the information to both sides of the brain.

8. Figure 14.3: Connections from the eyes to the human brain. (a) Route of visual input to the two hemispheres of the brain. Note that the left hemisphere is connected to the left half of each retina and thus gets visual input from the right half of the world; the opposite is true of the right hemisphere. (b) Closeup of olfactory bulbs and the optic chiasm. At the optic chiasm, axons from the right half of the left retina cross to the right hemisphere, and axons from the left half of the right retina cross to the left hemisphere.Figure 14.3: Connections from the eyes to the human brain. (a) Route of visual input to the two hemispheres of the brain. Note that the left hemisphere is connected to the left half of each retina and thus gets visual input from the right half of the world; the opposite is true of the right hemisphere. (b) Closeup of olfactory bulbs and the optic chiasm. At the optic chiasm, axons from the right half of the left retina cross to the right hemisphere, and axons from the left half of the right retina cross to the left hemisphere.

9. Lateralization of Function Damage to the corpus callosum interferes with the exchange of information between hemispheres. Epilepsy is a condition characterized by repeated episodes of excessive synchronized neural activity. Mainly due to decreased release of the inhibitory neurotransmitter GABA. Physicians once cut the corpus callosum to prevent the seizure from spreading to the opposite side of the body.

10. Lateralization of Function People who have undergone surgery to the corpus callosum are referred to as split-brain people. Spit brain people maintain normal intellect and motivation but they tend to: Use hands independently in a way others cannot. Respond differently to stimuli presented to only one side of the body.

11. Figure 14.4: Effects of damage to the corpus callosum. (a) When the word hatband is flashed on a screen, (b) a woman with a split brain can report only what her left hemisphere saw, “band.” (c) However, with her left hand, she can point to a hat, which is what the right hemisphere saw.Figure 14.4: Effects of damage to the corpus callosum. (a) When the word hatband is flashed on a screen, (b) a woman with a split brain can report only what her left hemisphere saw, “band.” (c) However, with her left hand, she can point to a hat, which is what the right hemisphere saw.

12. Lateralization of Function Sperry (1974) revealed subtle behavioral differences for spilt brain people. Because the left side of the brain is dominant for language in most people, most split brain people: Have difficulty naming objects briefly viewed in the left visual field. A small amount of information can still be transferred via several smaller commissures.

13. Figure 14.5: The anterior commissure and hippocampal commissures. These commissures allow for the exchange of information between the two hemispheres, as does the larger corpus callosum. (Source: Based on Nieuwenhuys, Voogd, & vanHuijzen, 1988, and others)Figure 14.5: The anterior commissure and hippocampal commissures. These commissures allow for the exchange of information between the two hemispheres, as does the larger corpus callosum. (Source: Based on Nieuwenhuys, Voogd, & vanHuijzen, 1988, and others)

14. Lateralization of Function Immediately after surgery, each hemisphere can only quickly and accurately respond to information that reaches it directly. Smaller commissures allow a slower response. The brain later learns use the smaller connections: Difficulty integrating information between both remains.

15. Figure 14.6: Left-hand drawing by a split-brain patient. He saw the word sky in the left visual field and scraper in the right visual field. His left hemisphere controlled the left hand enough to draw a scraper, and his right hemisphere controlled it enough to draw a sky. Neither hemisphere could combine the two words to make the emergent concept skyscraper. (Source: From “Subcortical Transfer of Higher Order Information: More Illusory Than Real?” by A. Kingstone and M. S. Gazzaniga, 1995. Neuropsychology, 9, pp. 321–328. Copyright © 1995 American Psychological Association. Reprinted with permission)Figure 14.6: Left-hand drawing by a split-brain patient. He saw the word sky in the left visual field and scraper in the right visual field. His left hemisphere controlled the left hand enough to draw a scraper, and his right hemisphere controlled it enough to draw a sky. Neither hemisphere could combine the two words to make the emergent concept skyscraper. (Source: From “Subcortical Transfer of Higher Order Information: More Illusory Than Real?” by A. Kingstone and M. S. Gazzaniga, 1995. Neuropsychology, 9, pp. 321–328. Copyright © 1995 American Psychological Association. Reprinted with permission)

16. Lateralization of Function Right hemisphere is better at perceiving emotions. Damage to parts of the right hemisphere causes difficulty perceiving other’s emotions, failure to understand humor and sarcasm, and a monotone voice. Left hemisphere damage increases ability to accurately judge emotion. Associated with decreased interference from the left hemispheres.

17. Lateralization of Function The right hemisphere is also better at comprehending spatial relationships. In general, the left hemisphere seems to focus more on visual details, and the right hemisphere focuses more on visual patterns.

18. Lateralization of Function Some anatomical differences exist between the hemispheres of the brain. The planum temporale is an area of the temporal cortex that is larger in the left hemisphere in 65% of people. Difference are slightly greater for people who are strongly right handed. MRI studies indicate that the a big difference in the ratio of left to right planum temporale is related to increased language performance.

19. Figure 14.9: Horizontal section through a human brain. This cut, taken just above the surface of the temporal lobe, shows the planum temporale, an area that is critical for speech comprehension. Note that it is substantially larger in the left hemisphere than in the right hemisphere. (Source: Based on “Human brain: left-right asymmetries in temporal speech region,” by N. Geschwind and W. Levitsky, 1968, Science, 161, pp. 186–187. Copyright © 1968 by AAAS and N. Geschwind.)Figure 14.9: Horizontal section through a human brain. This cut, taken just above the surface of the temporal lobe, shows the planum temporale, an area that is critical for speech comprehension. Note that it is substantially larger in the left hemisphere than in the right hemisphere. (Source: Based on “Human brain: left-right asymmetries in temporal speech region,” by N. Geschwind and W. Levitsky, 1968, Science, 161, pp. 186–187. Copyright © 1968 by AAAS and N. Geschwind.)

20. Lateralization of Function Damage to left hemisphere often results in language deficiencies. Left side seems to be specialized for language from the very beginning in most people. The corpus callosum matures gradually through the first 5 to 10 years. Thus, young children have difficulty comparing information from the left and right hand.

21. Lateralization of Function Being born with a condition where the corpus callosum does not completely develop results in extra development of the following: Anterior commissure - connects the anterior parts of the cerebral cortex. Hippocampal commissure - connects the left and right hippocampus. Allows performance on some tasks that differs from split-brain people.

22. Lateralization of Function The left hemisphere is dominant for speech in 95% of right-handed people. Most left-handers have left-hemisphere or mixed-dominance for speech. Few people have strong right hemisphere dominance.

23. Lateralization of Function Recovery of language after damage to the brain varies. Age affects extent of recovery. Brain is more plastic at an early age. Right hemisphere reorganizes to serve some of the left-hemisphere function.

24. Lateralization of Function Rasmussen’s encephalopathy is a rare condition in which the immune system initially attacks the glia and then the neurons of one hemispheres of the brain. Usually begins in childhood or adolescence. Surgeons eventually remove or disconnect the side of the damaged brain. Language recovers slowly but substantially. Slow deterioration allows the other side of the brain to compensate and reorganize.

25. Lateralization of Function Language recovery after brain damage is also influenced by how language was initially lateralized for the given person. Individuals with partial representation of language in both hemispheres recover better than those with language dominance in one hemisphere.

26. Evolution and Physiology of Language Human language is a complex form of communication. Compared to other species, human language has high productivity. Productivity - the ability to produce new signals to represent new ideas.

27. Evolution and Physiology of Language Human language is most likely a modification of a behavior also found in other species. Chimpanzees use language but it differs from humans: Seldom use symbols in new original combinations. Use of symbols lacks productivity. Use of symbols is primarily used to request and not describe. Production of requests is better than understanding other’s requests.

28. Evolution and Physiology of Language Bonobos or pygmy chimpanzees show an increased comprehension of human language: Understand more than they can produce. Use symbols and names to describe objects. Request items not seen. Use symbols to describe past events. Make original, creative requests.

29. Lateralization of Function Non-primates also display some aspects of spoken language. Elephants imitate sounds they hear, including the vocalizations of other elephants. Dolphins respond to gestures and sounds. The African gray parrot show a great ability for imitating sounds and also using sounds meaningfully. Example: Alex the gray parrot.

30. Evolution and Physiology of Language Studies of nonhuman language abilities: Give insights to how best to teach language to those who do not learn it easily. Examples: Brain damaged people or children with autism. Illustrate the ambiguity of our concept of language. Allows for more precise definition.

31. Evolution and Physiology of Language Two categories of theories attempt to explain the human ability to learn language more easily than other species. “Language evolved as a by-product of overall brain development.” “Language evolved as an extra part of the brain.”

32. Evolution and Physiology of Language Problems associated with the “language as a by-product of increased intelligence” theory: People with a full-size brain and normal overall intelligence can show severe language deficits. People with impaired intelligence can have normal language skills. Williams syndrome characterized by metal retardation but skillful use of language.

33. Figure 14.14: A drawing and a description of an elephant by a young woman with Williams syndrome. The labels on the drawing were provided by the investigator based on what the woman said she was drawing. (Source: From “Williams syndrome: An unusual neuropsychological profile,” by U. Bellugi, P. P. Wang, and T. L. Jernigan, In S. H. Broman and J. Grafman, Eds., Atypical Cognitive Deficits in Developmental Disorders. Copyright © 1987 Lawrence Erlbaum. Reprinted by permission.)Figure 14.14: A drawing and a description of an elephant by a young woman with Williams syndrome. The labels on the drawing were provided by the investigator based on what the woman said she was drawing. (Source: From “Williams syndrome: An unusual neuropsychological profile,” by U. Bellugi, P. P. Wang, and T. L. Jernigan, In S. H. Broman and J. Grafman, Eds., Atypical Cognitive Deficits in Developmental Disorders. Copyright © 1987 Lawrence Erlbaum. Reprinted by permission.)

34. Evolution and Physiology of Language Evidence suggesting language evolved as an extra brain module specialization includes: Language acquisition device is a built in mechanism for acquiring language. Evidence comes from the ease at which most children develop language. Chomsky (1980) further suggests the poverty of stimulus argument: children do not hear many examples of some of the grammatical structures they acquire.

35. Evolution and Physiology of Language Most researchers agree that humans have a specially evolved “something” that enables them to learn language easily. Certain brain areas are indeed necessary for language. But same areas are also necessary for other tasks (memory and music perception). Exactly how humans evolved language is unknown but is perhaps due to the pressure for social interaction.

36. Evolution and Physiology of Language Research suggests a critical period exists for the learning of language. Learning of a second language differs as a function of age: Children are better at learning pronunciation and unfamiliar aspects of grammar. No sharp cutoff exist for second language learning. Adults learn a second-language vocabulary better.

37. Evolution and Physiology of Language Rare cases of children not exposed to language indicates limited ability to learn language later. Deaf children unable to learn spoken language and not given the opportunity to learn sign language while young reveals: Little development of skill at any language later. Early exposure to some language increases ability to learn another language later.

38. Evolution and Physiology of Language Most knowledge of brain mechanisms of language come from the study of people with brain damage: Broca’s area is a part of the frontal lobe of the left cerebral cortex near the motor cortex. Damage results in some language disability. Aphasia refers to a condition in which there is severe language impairment.

39. Evolution and Physiology of Language Broca’s aphasia/nonfluent aphasia refers to serious impairment in language production, usually due to brain damage. Omission of most pronouns, prepositions, conjunctions, auxiliary verbs, tense and number endings during speech production. People with Broca's aphasia have trouble understanding the same kinds of words they omit (prepositions and conjunctions).

40. Evolution and Physiology of Language Broca’s aphasia is usually accompanied by comprehension deficits when: The sentence meaning depends on prepositions, word endings or unusual word order. Sentence structure is complicated. Broca’s area thus seems to be critical for the understanding of some, but not all, aspects of grammar.

41. Figure 14.15: Some major language areas of the cerebral cortex. In most people, only the left hemisphere is specialized for language.Figure 14.15: Some major language areas of the cerebral cortex. In most people, only the left hemisphere is specialized for language.

42. Figure 14.16: Records showing blood flow for a normal adult. Red indicates the highest level of activity, followed by yellow, green, and blue. (a) Blood flow to the brain at rest. (b) Blood flow while subject describes a magazine story. (c) Difference between (b) and (a). The results in (c) indicate which brain areas increased their activity during language production. Note the increased activity in many areas of the brain, especially on the left side. (Source: Wallesch, Henriksen, Kornhuber, & Paulson, 1985)Figure 14.16: Records showing blood flow for a normal adult. Red indicates the highest level of activity, followed by yellow, green, and blue. (a) Blood flow to the brain at rest. (b) Blood flow while subject describes a magazine story. (c) Difference between (b) and (a). The results in (c) indicate which brain areas increased their activity during language production. Note the increased activity in many areas of the brain, especially on the left side. (Source: Wallesch, Henriksen, Kornhuber, & Paulson, 1985)

43. Evolution and Physiology of Language Wernicke’s area is an area of the brain located near the auditory part of the cerebral cortex. Wernicke’s aphasia is characterized by the impaired ability to remember the names of objects and also impaired language comprehension. Sometimes called “fluent aphasia” because the person can still speak smoothly. Recognition of items is often not impaired; ability to find word is impaired.

44. Evolution and Physiology of Language Typical characteristics of Wernicke’s aphasia include: Articulate speech / fluent speech except with pauses to find the right word. Difficulty finding the right word - anomia refers to the difficulty recalling the name of objects. Poor language comprehension - difficulty understanding spoken and written speech (especially nouns and verbs).

46. Evolution and Physiology of Language Dyslexia is a specific impairment of reading in a person with adequate vision and adequate skills in other academic areas. More common in boys. Research suggests a genetic influence.

47. Evolution and Physiology of Language In some cases, dyslexia is associated with mild abnormality in the structures of various brain areas. More likely to have a bilateral symmetrical cerebral cortex. Language–related areas in the right hemisphere are larger in some. Weak connections exist among other areas.

48. Evolution and Physiology of Language Different kinds of dyslexics have different reading problems. “Dysphonic dyslexics” have trouble sounding out words. Attempt to remember them as a whole. “Dyseidetic dyslexics” fail to recognize a word as a whole. Read slowly and have particular trouble with irregularly spelled words.

49. Evolution and Physiology of Language Most severe cases of “dyseidetic dyslexia” result from brain damage that restricts the field of vision. Characterized by the following: only seeing one letter a time. short eye movements. very slow reading. difficulty with long words.

50. Evolution and Physiology of Language One hypothesis to explain dyslexia emphasizes a hearing impairment rather than visual impairment. Less than normal response to speech sounds in the brain. Lack of ability to pay close attention to sounds.

51. Evolution and Physiology of Language Another hypothesis to explain dyslexia is connecting vision to sound. Brain scans indicate that reading strongly activates areas of the left temporal and parietal cortex for most people. Areas are associated with connecting visual and auditory information. Only weakly activated for people with dyslexia.

52. Evolution and Physiology of Language A final hypothesis relates dyslexia to differences in attention. Reading requires the shifting of attention. People with dyslexia do not shift their attention in the same way. Effective treatment may be for dyslexics to focus on one word at a time.

53. Figure 14.17: Identification of a letter at various distances from the fixation point. Normal readers identify a letter most accurately when it is closest to the fixation point, and their accuracy drops steadily as letters become more remote from that point. Many people with dyslexia show a small impairment for letters just to the right of the fixation point, yet they are substantially more accurate than normal readers are in identifying letters 5 to 10 degrees to the right of fixation. (Source: Reprinted from “Task-Determined Strategies of Visual Process,” by G. Geiger, J. Y. Lettvin, & U. Zegarra-Moran, 1992, Cognitive Brain Research, 1, pp. 39–52, 1992, with kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)Figure 14.17: Identification of a letter at various distances from the fixation point. Normal readers identify a letter most accurately when it is closest to the fixation point, and their accuracy drops steadily as letters become more remote from that point. Many people with dyslexia show a small impairment for letters just to the right of the fixation point, yet they are substantially more accurate than normal readers are in identifying letters 5 to 10 degrees to the right of fixation. (Source: Reprinted from “Task-Determined Strategies of Visual Process,” by G. Geiger, J. Y. Lettvin, & U. Zegarra-Moran, 1992, Cognitive Brain Research, 1, pp. 39–52, 1992, with kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)

54. Attention Attention is a multi-dimensional process and related to consciousness. Attention relates to increased brain activity in the areas responsive to a stimulus. Stimuli destined to become conscious or unconscious produce about the same brain activity in the first 200-250 milliseconds. In the next few milliseconds, the brain enhances activity for stimuli that become conscious.

55. Attention Enhancement of activity can be due to intensity of the stimulus, similarity to past important stimuli, or other features of the stimulus itself. Enhancement of activity can also be due to shifting of attention. Research suggests that attention pertains more to the enhancing of relevant activity than inhibiting irrelevant activity.

56. Attention “Inattention” or “neglect” is the opposite of attention. Spatial neglect is a tendency to ignore the left side of the body and its surroundings or the left side of objects. Often associated with damage to the right hemisphere of the brain.

57. Attention Exact location of the damage to the right hemisphere can affect the details of what the person neglects. Damage to the inferior part of the right parietal cortex leads to the neglect of everything to the left of their own body. Damage to the superior temporal cortex neglect the left side of objects, regardless of location.

58. Figure 14.19: Spatial neglect. A patient with neglect of the left side could identify the overall figures indicating that she saw the whole figures. However, when asked to cross off the elements that composed them, she crossed off only the parts on the right. (Source: Reprinted with permission from “Seeing the forest but only half the trees?” by J. C. Marshall and P. W. Halligan, Nature, 373, pp. 521–523. Copyright 1995 Nature Publishing Group.)Figure 14.19: Spatial neglect. A patient with neglect of the left side could identify the overall figures indicating that she saw the whole figures. However, when asked to cross off the elements that composed them, she crossed off only the parts on the right. (Source: Reprinted with permission from “Seeing the forest but only half the trees?” by J. C. Marshall and P. W. Halligan, Nature, 373, pp. 521–523. Copyright 1995 Nature Publishing Group.)

59. Attention Problems of neglect are associated with attention and not sensation. Someone with neglect can see an entire letter enough to say what it is. The same person ignores the left half when asked to cross out all the letters that compose a word.

60. Attention Several procedures can increase attention to the neglected side: telling the person to pay attention to the left side. telling the person to look left while feeling an object with the left hand or hearing a sound from the left side. A touch stimulus briefly increases attention to one side of the body or the other. Crossing of the hands in front of the body also decreases neglect to the left side.

61. Figure 14.20: A simple way to reduce sensory neglect. Ordinarily, someone with right parietal lobe damage neglects the left arm. However, if the left arm crosses over or under the right, attention to the left arm increases.Figure 14.20: A simple way to reduce sensory neglect. Ordinarily, someone with right parietal lobe damage neglects the left arm. However, if the left arm crosses over or under the right, attention to the left arm increases.

62. Attention Many patients with spatial neglect also have deficits with spatial working memory and with shifting attention, even when location is irrelevant. Thus, problems associated with neglect extend to many aspect of attention rather than simply the left-right dimension.

63. Attention Attention-Deficit Hyperactivity Disorder (ADHD) is characterized by the following: Attention deficits (distractibility). Hyperactivity (fidgetiness). Impulsiveness. Mood swings. Short temper. High sensitivity to stress. Impaired ability to make and follow plans.

64. Attention ADHD affects social behavior and school performance. Some have occupational problems and antisocial behaviors in adulthood. Estimates range from 3%-10% of children Twice or three times as likely in males. Research is complicated by the ability to make reliable diagnoses.

65. Attention Three example of tasks which people with ADHD differ: “The choice delay task” - more likely than others to choose a smaller but quicker reward (impulsiveness). “The stop signal task” - difficulty inhibiting behaviors. “The attentional blink task” - indicates trouble controlling attention and difficulty shifting it when needed.

66. Attention Twin studies suggest fairly high heritability (Thapar et al., 2003). Several genes have been identified which influence performance on tests of attention. ADHD probably depends on multiple genes as well as environmental influences. Probability of ADHD is elevated among children of women who smoked cigarettes during pregnancy.

67. Attention Structural brain differences include a smaller than average prefrontal cortex and cerebellum. Cerebellar dysfunction is known to be associated with difficulty switching attention. Structural differences in the brain are small and inconsistent between cases. Brain scans do not provide reliable results for diagnoses.

68. Attention The most common treatment for ADHD is stimulant drugs or amphetamines. Example: methylphenidate/Ritalin. Stimulant drugs increase attentiveness, improve school performance and social relationships, and decrease impulsiveness. Also improve scores on laboratory tests, such as the “stop signal task”. Justifying the benefits derived from taking the drugs is a complex and controversial issue.

69. Attention Amphetamines and methylphenidate increase the availability of dopamine to the postsynaptic receptors. Maximum benefit occurs 1 hour after ingestion and benefits last for a few hours. Several studies have found that stimulant drugs enhance certain aspects of learning and attention for all people, not just those with ADHD.

70. Attention Behavioral techniques are available as supplements or substitutes for stimulant drugs: Reduce distractions. Use lists, calendars, and other organizational techniques. Practice strategies to pace yourself. Learn to relax; tension and stress can magnify attention deficits.