ANATOMIC BASIS FOR LATERALIZATION speech lateralization in right-handers –following left...

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


hemisphereleft right both

right-handed 96% 4% 0%left-handed 70% 15% 15%

• most right-handed adults have speech represented in the left hemisphere

• Two hemispheres• Four lobes

– Frontal– Temporal– Parietal– Occipital

• Anatomic features– Sylvian fissure– Central sulcus– Broca’s area– Wernicke’s area– Arcuate fasciculus

B W


• 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


• less overlapping dendritic trees in left Wernicke’s area than right Wernicke’s area– more discrete processing for rapid transition of

speech sounds


• 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

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

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

FLUENCY

• Non-fluent speech– effortful– telegraphic– agrammatic

• Fluent speech– melodic– circumlocutory– empty content

COMPREHENSION

• Single word comprehension– Point to the pencil– [present two objects] - point to the pencil– [present one object] - is this a pencil?

SENTENCE COMPREHENSION

• sentence-picture matching

• Fran showed her baby the pictures

• Fran showed her the baby pictures


“make the blue block be above the white block”

Object manipulation

REPETITION

• Multi-syllabic words– “constitutional”

• Phrases– “methodist episcopal”

• Sentences– “no ifs, ands, or buts”

NAMING

• Confrontation naming– name demonstrated object spontaneously

• Recognition naming– choose correct name for demonstrated

object

• Prompts– semantic– phonemic

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

BROCA’S APHASIA

• non-fluent speech• effortful, telegraphic, agrammatic

• comprehension• intact single word comprehension• agrammatic sentence comprehension

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


• 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


• 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

• 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


• 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


• 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

60

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.

*


• 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


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?


• 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


• 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


• 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


• 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


• Sentence comprehension comparing 11 healthy seniors and 13 young subjects for object-relative long linkage sentences– A: seniors > young– B: seniors < young

FRONTOTEMPORAL DEGENERATION

• Clinical subgroups– Progressive aphasia– Executive limitation– Personality change

• MRI scan– Relative atrophy in

frontal and temporal distribution

LR

PROGRESSIVE NON-FLUENT APHASIA

• Expression– hesitant, effortful, telegraphic speech

• oral, written

• Comprehension– agrammatic sentence comprehension

• oral, reading

PERFUSION fMRI IN FTD

• Grammatical aspects of sentence comprehension in FTD are correlated with left frontal defect

DYSEXECUTIVE SYNDROME

• limited working memory• impaired planning, problem-solving• inhibitory control deficit

– perseverative, echolalic, perceptually bound, impulsive

PERFUSION fMRI IN FTD

• Semantically-guided category naming fluency in FTD is correlated with left frontal defect

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

-4

-3

-2

-1

0

z-sc

ore

PNFA

EXEC

SD

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

ANATOMIC BASIS FOR LATERALIZATION speech lateralization in right-handers –following left...

Documents

Transcript of ANATOMIC BASIS FOR LATERALIZATION speech lateralization in right-handers –following left...