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Lateralization of Language ch.16 (cont’d) and Biopsychology of Memory ch. 11. Lateralization and Cortical Localization of Language. Ch. 16 (cont’d). Outline. Differences Between the Left and Right Hemispheres Broca’s Area Wernicke’s Area. Differences Between The Left and Right Hemispheres.

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Lateralization of Language ch.16 (cont’d) and Biopsychology of Memory ch. 11

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Lateralization of language ch 16 cont d and biopsychology of memory ch 11 l.jpg

Lateralization of Languagech.16 (cont’d)andBiopsychology of Memorych. 11


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Lateralizationand Cortical Localization of Language

Ch. 16 (cont’d)


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Outline

  • Differences Between the Left and Right Hemispheres

  • Broca’s Area

  • Wernicke’s Area


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Differences BetweenThe Left and Right Hemispheres

  • Language is the most lateralized of all abilities; the left-hemisphere is better than the right at most language-related tasks

  • however, the right hemisphere proved to be able to understand single written and spoken words (video); also right-hemisphere detects prosody and discourse


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Differences BetweenThe Left and Right Hemispheres

  • The right hemisphere proved better than the left at a variety of tasks involving spatial ability, emotional stimuli and musical tasks

  • LH hippocampus is associated with verbal memory and RH hippocampus is associated with spatial memory


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Differences BetweenThe Left and Right Hemispheres

  • The two hemispheres seem to engage different types of memory processing; LH attempts to place its experience in a larger context (relation of parts that make up the whole), while the RH attends strictly to the Gestalt perceptual characteristics of the stimulus (either the parts or whole but not relation between)

  • This is usually termed analytical (LH) versus holistic (RH)


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Differences BetweenThe Left and Right Hemispheres

  • Thus the RH should not be regarded as the minor hemisphere; it has different abilities, not less important ones


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Differences BetweenThe Left and Right Hemispheres

  • There are also anatomical asymmetries in the human brain; for example the planum temporale and frontal operculum (language related areas) are larger in LH

  • However, Heschl’s gyrus (also language related) in larger in RH


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Differences BetweenThe Left and Right Hemispheres

  • (not in book) left-handers seem to have symmetrical planum temporales, suffer less severely from LH aphasia, and suffer more severely from RH aphasia

  • This suggests left-handers may have a more diffuse representation of language and is evident in differential strategies in sentence processing


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Differences BetweenThe Left and Right Hemispheres

  • For example in priming studies, when the target word is LILY, right-handers are quicker at deciding that it as a word if they are primed with the word ROSE, where as left-handers are quicker at deciding if primed with the word POND


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Differences BetweenThe Left and Right Hemispheres

  • LILY and ROSE fit same syntactic templates

    • i.e., The ___ bloomed. The ___ is a flower.

  • LILY and POND are associated in real world semantic representation


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Three Theories ofCerebral Asymmetry

  • Analytic-synthetic theory

  • Motor theory

  • Linguistic theory


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Analytic-Synthetic Theory

  • Suggests that there are two fundamentally different modes of thinking, an analytic mode (LH) and synthetic mode (RH), and that the neural circuitry for each is fundamentally different

  • LH (pieces of the whole) operates in logical, sequential, analytic fashion

  • RH (the whole) makes immediate, overall synthetic judgments


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Analytic-Synthetic Theory

  • Experienced musicians are left-hemisphere dominant for processing music


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Motor Theory

  • Posits that LH is specialized for fine motor movement of which speech is but one example

  • Two lines of evidence:

    • Lesions of the LH disrupt facial movements more than do RH lesions, even when they are not related to speech

    • Degree of disruption of nonverbal facial movements is positively correlated with the degree of aphasia


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Linguistic Theory

  • Based on the view that the primary function of the LH is language; this is based on studies of deaf people who communicate using ASL; this ability is lost if these people suffer damage to the LH, even when they are able to make the movements required

  • (or is this just showing ASL is a language, or that language is highly analytical or that ASL requires fine motor movements of the hand like speech does of the mouth/tongue?)


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Broca’s Area

  • Inferior left prefrontal area in left hemisphere

  • Damage leads to deficits primarily in speech production (problems with expression) and also grammatical comprehension


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Wernicke’s Area

  • Left posterior temporal area, just posterior to the primary auditory cortex

  • Damage leads to deficits to semantic language comprehension (problems with reception) and speech is semantically incomprehensible, despite having correct grammar, rhythm and intonation (word salad)


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  • Broca’s area (Broadmann’s area 44 and 45)

  • Wernicke’s area (narrowly defined as BA22 but can also describe BA37, 39 and 40).


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Conduction Aphasia

  • Damage to white matter (heavily myelinated) tract connecting Broca’s and Wernicke’s areas called the arcuate fasciculus

  • Comprehension and spontaneous speech are intact but patient not able to repeat words they have just heard


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Arcuate fasciculus


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Arcuate fasciculus


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Conduction Aphasia

  • However, conduction aphasics (temporoparietal lesions) are a heterogeneous group in terms of impairment (some more Broca’s aphasic - like, some Wernicke’s aphasic - like) suggesting arcuate fasciculus may not be the only underlying structure


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Perisylvian language networks of the human brain (Catani, et al., 2005)

  • Newly discovered but evolutionarily older structure in addition to the classical arcuate fasciculus

    • parallel and lateral to classical arcuate fasciculus

    • Connects “Geschwind’s territory” (inferior parietal cortex that receives multimodal inputs important for semantics; BA39 and 40) to classical language areas (Broca’s and Wernicke’s areas)

    • Rudimentary form of this network exists in the brain of other primates (macaque monkey)


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Perisylvian language networks of the human brain (Catani, et al., 2005)

Arcuate fasciculus (unique to humans; long segment; medial)

and other network(anterior segmentand posterior segment)


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Perisylvian language networks of the human brain (Catani, et al., 2005)

  • Corroborates neuropsychological evidence for different types of conduction aphasics

    • Classical conduction aphasia (long segment lesion; failure in automatic repetition)

    • Transcortical aphasia (anterior segmentlesion; failure to vocalize semantic content)

    • Sensory aphasia (posterior segment lesion; failure of auditory semantic comprehension)


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  • Broca’s area (Broadmann’s area 44 and 45)

  • Wernicke’s area (narrowly defined as BA22 but can also describe BA37, 39 and 40).


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Alexia

  • Damage to the left angular gyrus (area of left temporal and parietal cortex just posterior to Wernicke’s; BA39)

  • Inability to read despite intact language comprehension and production


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Agraphia

  • Also due to damage to the left angular gyrus

  • Inability to write despite intact language comprehension and production

  • Involvement of LAG in alexia and agraphia show its responsible for language related visual input


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Broca’s Aphasic Video(shown in class)


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Wernicke-Geshwind Model

  • Seven components in Left hemisphere: primary visual cortex, angular gyrus, primary auditory cortex, Wernicke’s area, arucate fasciculus, Broca’s area, and primary motor cortex


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Responding to a heard question

  • Primary auditory cortex to Wernicke’s area where comprehended

  • To respond, concept generated in Wernicke’s area, goes via arcuate fasciculus to Broca’s area, then to primary motor cortex and articulatory areas (face, lip, and tongue muscles, voice box, and muscles assoicated with lungs)

  • (animation in class)


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Reading aloud

  • Primary visual cortex to left angular gyrus, which transmits visual code to auditory code

  • Then to Wernicke’s area to arcuate fasciculus to Broca’s to primary motor cortex to articulatory areas

  • (animation in class)


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Evidence against W-G Model

  • Damage to these boundaries has little lasting effect on language

  • Damage to other brain areas can produce aphasia

  • Broca’s and Wernicke’s aphasia are rarely “pure” - aphasia is both receptive and expressive

  • Major individual differences for cortical localization for language


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Cognitive Neuroscience Approach to Language

  • Cannot perform lesion studies because humans are only known species with language

  • Use Cognitive Neuroscience (brain imaging like PET and fMRI) to study relation of brain and language


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Cognitive Neuroscience Approach to Language

  • Each of of the components in W-G model can be broken down further into constituent cognitive processes

    • Phonological analysis (sounds)

    • Grammatical analysis (structure)

    • Semantic analysis (meaning)


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Cognitive Neuroscience Approach to Language

(2) Areas of brain involved in language are not solely dedicated to language; many of the constituent cognitive processes also play roles in other behavior

Example - some areas involved in short-term memory and visual pattern recognition are involved in reading, too


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Cognitive Neuroscience Approach to Language

(3) W-G model assumes that brain areas involved in language are large, circumscribed, and homogenous but Cognitive Neuroscience assumes they are small, widely distributed, and specialized


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Dyslexia and Cognitive Neuroscience

  • Dyslexia is pathological difficulty in reading, does not result from general visual, motor, or intellectual deficits

  • Developmental dyslexia- apparent in childhood

  • Acquired dyslexia - damage in individuals who were already capable of reading


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Developmental Dyslexia

(1) Differences between brains of dyslexic and non-dyslexic readers have been reported, however none seems to play a critical role

Example - dyslexics do not display the asymmetry of the planum temporale


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Developmental Dyslexia

(2) Several types of dylexias and thus likely to have different causes and brain areas susceptible


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Developmental Dyslexia

(3) Difficult to determine cause-and-effect of brain abnormalities

Are these abnormalities the cause of dylexia or the result of lack of reading experience (brain develops differently as a result of different experience)?


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Acquired Dyslexia

  • Two strategies for reading aloud:

    • Lexical procedure - based on specific stored information that has been acquired about written words - looks at it, recognizes it and says it (yacht, aisle)

    • Phonetic procedure - looks at words, recognizes letters, sounds them out and says word (fish, river, glass)


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Acquired Dyslexia

  • Surface Dyslexia - patients lose ability to to pronounce words based on the specific memories of the words (they lose their lexical procedure)

  • Can pronounce non-words - wug

    Example: can pronoun words consistent with rules ( fish, river, or glass) but can’t pronounce unusual words (have, lose, and steak are like cave, hose, and beak)


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Acquired Dyslexia

  • Deep Dyslexia - patients lose ability to apply common rules of pronunciation ( they lose their phonetic procedure)

  • Can’t pronounce non-words

    Example: can say phonetically unusual words like aisle and yacht but cannot pronounce rule-consistent words like fish, river, or glass


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Acquired Dyslexia

  • Where are lexical and phonetic processes in the brain?

  • Deep dyslexia (lose phonetic procedure) due to damage in LH

  • Surface dyslexia (lose lexical) due to partial LH damage or RH damage


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The Neuropsychologyof Memory

Ch. 11


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Outline

  • Review of memory terms

  • Amnesic Effects of Bilateral Medial Temporal Lobectomy

  • The case of H.M.


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Learning vs. Memory

  • Learning deals with how experience changes the brain and memory refers to how these changes are stored and later retrieved

  • We have learned much about the neural mechanisms of memory by studying amnesic patients


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Types of Memory

  • Episodic memory - explicit and declarative

  • Semantic memory - explicit and non-declarative

  • Procedural memory - implicit and non-declarative


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Amnesic Effects of Bilateral Medial Temporal Lobectomy

  • H.M. suffered from severe, intractable epilepsy; he seemed to have epileptic foci in both medial temporal lobes

  • A bilateral medial temporal lobectomy was prescribed for H.M.; this included the removal of the hippocampus and amygdala


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Amnesic Effects of Bilateral Medial Temporal Lobectomy

  • In some respects, the operation was a success: H.M.’s convulsions were reduced in severity and frequency and his IQ increased from about 104 to 118, however…


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Amnesic Effects of Bilateral Medial Temporal Lobectomy

  • H.M. suffered from devastating amnesia as a result of his operation


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H.M.’s Memory Deficits

  • H.M. has minor retrograde amnesia (can’t remember events before his surgery) for events of the 2 years preceding the surgery

  • He has normal memory for remote events and normal short-term memory (his digit span is about 6)


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H.M.’s Memory Deficits

  • However, he cannot form long-term memories for events that occurred after his surgery

  • This is called anterograde amnesia. For example, he has no memory of his new home, his new job, or new friends


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H.M.’s Memory Deficits

  • At first, it was assumed that H.M. could not form long-term memories at all, but objective testing revealed that H.M. can demonstrate his retention of certain types of tasks by his improved performance on them, although he has no conscious recollection of previously practicing them


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H.M.’s Memory Deficits

  • H.M.’s deficits can be described in terms of his performance on six objective tests of memory:


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H.M.’s Memory Deficits

  • Digit Span +1 Test: after 25 trials with the same series of digits, he could do only 7 digits, just one more than his normal memory span

  • Block-Tapping Memory-Span Test: his block-tapping memory-span was normal; but he could not extend it, even by one, when the same sequence was repeated for 12 trials


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H.M.’s Memory Deficits

  • Mirror-Drawing Test: he displayed substantial savings with no conscious recall of previous practice

  • Rotary-Pursuit Test: he displayed substantial savings with no conscious recall of previous practice


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H.M.’s Memory Deficits

  • Incomplete-Picture Test: after seeing 5 sets of 20 line drawings of varying completeness, he displayed substantial savings with no conscious recall of the drawings

  • Pavlovian Conditioning: tones and a puff of air to the eye were presented to H.M.; he blinked in response; two years later he retained this conditioned pairing almost perfectly although he had no conscious awareness of his previous training


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H.M.’s Memory Deficits

  • H.M.’s case had the following significant influences on the study of memory:

    • It showed that the medial temporal lobes are important to mnemonic functions

    • It challenged the view that mnemonic functions are diffusely represented throughout the brain


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H.M.’s Memory Deficits

  • It renewed efforts to related specific brain structures to specific mnemonic processes

  • It supported the theory that there is a different mode of storage for short-term and long-term memories

  • H.M.’s case provided the first evidence that implicit memory could survive in the absence of explicit memory


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Medial Temporal Lobe Amnesia

  • H.M.’s ability to form implicit, but not explicit, long-term memories is often seen in cases of medial temporal lobe amnesia, as well as other amnesic disorders


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Medial Temporal Lobe Amnesia

  • Repetition priming tests are used to assess implicit memory; patients are shown a list of words and sometime later they are shown a series of word fragments and asked to complete the words

  • Amnesic patients do as well on this task as control subjects, even though they do not remember ever seeing the original list of words


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Medial Temporal Lobe Amnesia

  • Recent research has suggested that problems with episodic memory (memories for the events of one’s own life) are more common than problems with semantic memory (memories for general facts or information) in patients suffering from medial temporal lobe amnesia


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Medial Temporal Lobe Amnesia

  • The fact that implicit are intact while explicit memories are compromised in patients suffering from MTL amnesia raises the question

    “Why do we have 2 memory systems… one conscious, and the other unconscious?”


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Medial Temporal Lobe Amnesia

  • The answer seems to be differential flexibility; implicit memories do not transfer well to different contexts, whereas explicit memories can


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