anatomic basis for lateralization speech lateralization in right-handers –following left...
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ANATOMIC BASIS FOR LATERALIZATION
• speech lateralization in right-handers– following left hemisphere insult in 97% of stroke patients– following left hemisphere insult in 95% of head trauma patients– following left carotid Wada test in 95% of patients
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ANATOMIC BASIS FOR LATERALIZATION
hemisphereleft right both
right-handed 96% 4% 0%left-handed 70% 15% 15%
• most right-handed adults have speech represented in the left hemisphere
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• Two hemispheres• Four lobes
– Frontal– Temporal– Parietal– Occipital
• Anatomic features– Sylvian fissure– Central sulcus– Broca’s area– Wernicke’s area– Arcuate fasciculus
B W
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ANATOMIC BASIS FOR LATERALIZATION
• planum temporale larger in left hemisphere than right hemisphere in dextrals
• left Sylvian fissure longer and more horizontal than right Sylvian fissure in dextrals
• left inferior frontal cortex larger in left hemisphere than right hemisphere
• similar asymmetries in neonates, early hominids, some great apes
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ANATOMIC BASIS FOR LATERALIZATION
• less overlapping dendritic trees in left Wernicke’s area than right Wernicke’s area– more discrete processing for rapid transition of
speech sounds
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ANATOMIC BASIS FOR LATERALIZATION
• speech lateralization in left-handers– sinistrals more likely to be aphasic following left
hemisphere insult or right hemisphere insult• aphasia milder and briefer in left-handers• aphasia milder and briefer in mixed-handers and in
patients with mixed family handedness
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ENVIRONMENTAL BASIS FOR LATERALIZATION
• speech lateralization is affected by experience– right-handed illiterates and partial illiterates are less
likely to have strongly lateralized speech • aphasia follows insult to the left hemisphere or the right
hemisphere in illiterate right-handers
– aphasia for a recently acquired second language can follow right hemisphere insult in a right-hander, sparing the mother tongue in left hemisphere
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APHASIA SYNDROMES
FLUENCY COMPREHENSION REPETITION NAMINGNON-FLUENTBroca's poor good poor poorGlobal poor poor poor poor
FLUENTWernicke's good poor poor poorConduction good good poor good
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FLUENCY
• Non-fluent speech– effortful– telegraphic– agrammatic
• Fluent speech– melodic– circumlocutory– empty content
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COMPREHENSION
• Single word comprehension– Point to the pencil– [present two objects] - point to the pencil– [present one object] - is this a pencil?
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SENTENCE COMPREHENSION
• sentence-picture matching
• Fran showed her baby the pictures
• Fran showed her the baby pictures
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SENTENCE COMPREHENSION
“make the blue block be above the white block”
Object manipulation
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REPETITION
• Multi-syllabic words– “constitutional”
• Phrases– “methodist episcopal”
• Sentences– “no ifs, ands, or buts”
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NAMING
• Confrontation naming– name demonstrated object spontaneously
• Recognition naming– choose correct name for demonstrated
object
• Prompts– semantic– phonemic
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APHASIA SYNDROMES
FLUENCY COMPREHENSION REPETITION NAMINGNON-FLUENTBroca's poor good poor poorGlobal poor poor poor poor
FLUENTWernicke's good poor poor poorConduction good good poor good
B W
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BROCA’S APHASIA
• non-fluent speech• effortful, telegraphic, agrammatic
• comprehension• intact single word comprehension• agrammatic sentence comprehension
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SENTENCE COMPREHENSION IN BROCA’S APHASIA
0
20
40
60
80
100
subj
ect-
rela
tive
obje
ct-
rela
tive
% c
orre
ct
• Good comprehension of sentences with typical word order
• Poor comprehension of sentences with non-canonical word order
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SENTENCE COMPREHENSION
• grammatical role is assigned indirectly via a trace that is phonetically silent
The eaglei that ti chased the hawk was fast.
• grammatical role assignment in sentences with subject-relative center-embedded clauses
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SENTENCE COMPREHENSION
• word order is non-canonical• the antecedent noun must be kept in mind for
many words until the trace is encountered
The eaglei that the hawk chased ti was fast.
• grammatical role assignment in sentences with object-relative center-embedded phrases
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• impaired grammatical phrase structure knowledge– loss of traces– without traces, grammatical roles assigned on the basis
of alternative strategies• use of semantic constraint
– The worm that the eagle ate was tasty
• dependence on word order strategy– First noun is subject/agent
SENTENCE COMPREHENSION IN BROCA’S APHASIA
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• processing limitations– slowed lexical retrieval impairs grammatical processing
• on-line processing of grammatical phrases limited by failure to retrieve words exactly when needed in course of sentence processing
SENTENCE COMPREHENSION IN BROCA’S APHASIA
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• slowed lexical retrieval during semantic priming
• slowed trace retrieval in object-relative center-embedded sentences– cross-modality lexical decision
priming the trace at gap and pregap locations
– Swinney et al, 1996
-20
0
20
40
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80
100
120
140
pregap gap
con
tro
l - e
xper
imen
tal m
sec
Broca's
Wernicke's
The eagle that the hawk with brown feathers *P* chased *G* was fast.
*
SENTENCE COMPREHENSION IN BROCA’S APHASIA
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• processing limitations– Verbal short-term memory limitation
• Poor retention of head noun until trace is encountered while processing sentence material
– Broca’s aphasics have impaired verbal short-term memory
SENTENCE COMPREHENSION IN BROCA’S APHASIA
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fMRI SENTENCE COMPREHENSION
• subject-relative– Short linkage– Long linkage
• object-relative– short linkage– long linkage
• FOUR SENTENCE CONDITIONS
• PROBE AGENT OF ACTION– did male or female perform action in sentence?
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fMRI SENTENCE COMPREHENSION
• GRAMMATICAL FACTOR– subject-relative center-embedded sentence
• grammatically simpler (typical word order)• The boyi from Boston that ti chased the girl with
the long brown hair is friendly
– object-relative center-embedded sentence• grammatically more complex (non-canonical
word order)• The boyi that the girl chased ti with the long
brown hair from Boston is friendly
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fMRI SENTENCE COMPREHENSION
• COGNITIVE RESOURCE FACTOR– short linkage sentence
• less working memory demands
• The boyi from Boston that ti chased the girl with the long brown hair is friendly
– long linkage sentence• more working memory demands
• The boyi with the long brown hair from Boston that ti chased the girl is friendly
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SENTENCE COMPREHENSION
• Sentence comprehension compared to pseudofont baseline in 15 young healthy adults– A: subject-relative short linkage– B: subject-relative long linkage– C: object-relative short linkage– D: object-relative long linkage
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SENTENCE COMPREHENSION
• Sentence comprehension compared to pseudofont baseline in 11 healthy seniors with good comprehension– A: subject-relative short linkage– B: subject-relative long linkage– C: object-relative short linkage– D: object-relative long linkage
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SENTENCE COMPREHENSION
• Sentence comprehension comparing 11 healthy seniors and 13 young subjects for object-relative long linkage sentences– A: seniors > young– B: seniors < young
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FRONTOTEMPORAL DEGENERATION
• Clinical subgroups– Progressive aphasia– Executive limitation– Personality change
• MRI scan– Relative atrophy in
frontal and temporal distribution
LR
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PROGRESSIVE NON-FLUENT APHASIA
• Expression– hesitant, effortful, telegraphic speech
• oral, written
• Comprehension– agrammatic sentence comprehension
• oral, reading
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PERFUSION fMRI IN FTD
• Grammatical aspects of sentence comprehension in FTD are correlated with left frontal defect
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DYSEXECUTIVE SYNDROME
• limited working memory• impaired planning, problem-solving• inhibitory control deficit
– perseverative, echolalic, perceptually bound, impulsive
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PERFUSION fMRI IN FTD
• Semantically-guided category naming fluency in FTD is correlated with left frontal defect
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SENTENCE COMPREHENSION IN FTD SUBGROUPS
• Comprehension of sentences with subordinate clauses
• PNFA patients more impaired than EXEC patients
• 100% of individual PNFA patients differ significantly from healthy controls
-5
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0
z-sc
ore
PNFA
EXEC
SD
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CORTICAL RECRUITMENT DURING SENTENCE COMPREHENSION IN FTD
– PNFA patients (n=3) with grammatical comprehension difficulty do not recruit left inferior frontal cortex (BA 45/47)
– EXEC patients (n=5) with limited short-term memory do not recruit BA 6/44
PNFA patients
EXEC patients