A Neurolinguistic Introduction to Aphasia

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A Neurolinguistic Introduction

to Aphasia

Cognitive Sciences

2006



Outline

• Aphasia and language

• Double dissociations

• Localization of (linguistic) function• Broca, Wernicke, and the syndrome

approach to aphasia

• Behavioral studies of aphasia• Neuroimaging studies of aphasia



Patient B: "Well it's a it's a place and it's a g-girl and a boy . . . and the-they've got

obviously something which is made made made well it's just beginning to go and

be rather unpleasant ha! ha! And this is in the this is the the woman and she's

putting some stuff and the it's it's that's being really too big to do and nobody

seems to have got anything there at all and it's . . . I'm rather surprised that butthere you are this this stuff this is coming they were both being one and another

put here and um I suppose the idea is that the two people should be fairly good

but I think it's going somewhere and as I say it's down again . . . let's see what

else has gone the this is just I don't know how she how they did this but it must

have been fairly hard when they did it and I think there isn't very much there I

think."

• Patient A: (Points to the water and

laughs) "Ah . . . ah . . . girl and boy,

ah oh er er dear . . . girl (points to

the woman) cof (points to the cloth)

and, er oh er dear me . . . er (points

to the stool) er steps um window,

curtains . . . a pot and an er (pointsto the water) oh dear me . . . OK"

Aphasic language production



Defining aphasia

Rao 1994



Defining language

• Speech?

• Communication?

• Thought?• A separate system of knowledge?

• Double dissociations



Double dissociations

• Cognitive systems dissociate from one another • One can be impaired while another is (relatively) spared

• This is taken as evidence that cognitive systems are likelydistinct from one another – the brain/mind is MODULAR inits organization

• Language is not a monolith

• Dissociations require caution:

- maybe one function is just more vulnerable to certainkinds of damage than another

- one task might be more „difficult‟ than another

- Apparent dissociations might arise from non-modular systems



Single word reading by two alexic patients: Warrington 1981, Patterson 1979, Plaut & Shallice 1993



Localization of function

•

Phrenology – Gall, Spurzheim, early1800s

• Different cognitive functions can be

localized to different parts of the brain

• Level of development of a particular function is reflected in skull formation

• The sad tale of Phineas Gage• Dissociation of language from other

cognitive faculties



Localization of language

• Paul Broca (1861): patient„Tan‟

• Slow, effortful, nonfluent

speech with many omissions;

but good comprehension

• on parle avec l’hemisphere

gauche

• Carl Wernicke: patientswith posterior lesions in

the left hemisphere

• comprehension is

impaired but speech isfluent



From the Whole Brain Atlas at Harvard Medical School :

http://www.med.harvard.edu./AANLIB/home.html



Wernicke‟s prediction

• Predicted two languagecenters:

– Broca‟s area: speech

articulation

– Wernicke‟s area: speechcomprehension

• Predicted a third

„disconnection‟ syndrome

– damage to the arcuatefasciculus

• “Conduction aphasia”

Chris Rorden, University of Nottinghamhttp://www.psychology.nottingham.ac.uk/staff/cr1/c83lnp/c83lnp2.pdf



Wernicke-Lichtheim model

Wernicke‟s area Broca‟s area

Concepts (distributed)

arcuate

fasciculus

Broca’s aphasia Wernicke’s aphasia

conduction

aphasia

Conduction aphasia: can produce and understand meaningful speech, but cannot

repeat words they hear







Classifying the aphasias

• Advantages of classifying patients into syndromes – increases interscientist communication

– groups homogeneous patients for research and for therapy

– describes a set of behaviors for diagnostic purposes

– can help in determining a prognosis

– contribute data toward localization of lesion - advancing our understanding of the relations between brain and mind

• Disadvantages of syndrome approaches – limits thought

– exceptions may be more interesting and more fruitful for research – may force a label onto a patient who does not really fall into a

particular syndrome category

– presumes too much about premorbid functioning

– localization issues may be vexed by individual differences



U d t di ti



Understanding agrammatism: a

central syntactic deficit?• Caramazza and Zurif 1976: agrammatics do have a comprehension

deficit, and it parallels their production disabilities• The test case: Semantically reversible sentences

• Theta-roles: assignment of interpretive roles to syntactic objects

subject verb object Grammatical roles

John kissed MaryTheta roles

• Non-canonical word order reliance on grammatical structure

object verb subject

John was kissed by Mary

• “…central disruption of the syntactic parsing component of thelanguage system” Berndt & Caramazza 1980

Agent Patient

Agent?? Patient??

U d t di ti



Understanding agrammatism: a

mapping deficit?

• Problems with the central syntactic deficit account: – agrammatics do have some ability to interpret complex

utterances - in particular, they are quite good at

grammaticality judgment – Some agrammatics are modality-specifically impaired –

note assumptions of central deficit hypothesis

– Some fluent aphasics show comprehension deficitssimilar to those found in Broca‟s aphasics

• Perhaps the deficit is not central to syntax, butinvolves the transfer from syntactic structure tosemantic structure of a sentence: a mapping deficit

(Saffran et al 1980)



Understanding agrammatism: the

trace deletion hypothesis• We have seen that things move around in sentences

• And we have seen that interpreting sentences does not just mean knowing where the subject and the object are – it means knowing what theta roles to assign, too

• In the normal language system, movement leavestraces behind

• Theta roles can be assigned to traces , and thent ransmit ted to the moved item

• Grodzinsky (1990) asked: what if traces get deletedfrom the syntactic representation?

• Maybe this is what happens in agrammatism

• The trace deletion hypothesis



Trace Deletion Hypothesis• Assigning a theta role to „the girl‟

should be no problem – no trace

involved in that• P „by‟ assigns a theta role of Agent

– so „the girl = Agent

• But, if traces are deleted, then „the

boy‟ has no theta role • So follow your instincts – USUALLY, the first noun in asentence is the Agent

• So „the boy‟ is probably an Agent

• Now, the agrammatic thinks:„the boy‟ = Agent AND

„the girl‟ = Agent

• What to do? Guess at the right

interpretation of this sentence



Neuroimaging and aphasia

Price & Crinion 2005

f



Right hemisphere compensation after

aphasia

• Semantic processing of visually presented words: Gold &Kertesz 2000

• Patient GP with a large left hemisphere lesion, andprofound global aphasia, including extreme impairmentof auditory-verbal comprehension, speech and writing

• GP demonstrated considerable ability for semanticprocessing of visual words

• identified superordinate and subordinate visual wordsaccurately

• could distinguish proper written names from frequentnouns matched for initial letter and length

• could distinguish printed words representing living thingsfrom nonliving things

• performed well on the Pyramids and Palm Trees Test

(Howard & Patterson,1992)

Ri h h i h i f



Tasks: Shoe

Sock Hat

Semantic - Which of the lower words is more closely related to the top

one? (Response: L/R)

Orthographic – are all these words spelt correctly? (Response: Y/N)

Equally good behavioral results on all items, for both participants

fMRI Subtraction: Semantic - Orthographic

Right hemisphere compensation after

aphasia



Changes in compensatory

activations post-stroke• Fernandez et al 2004: PL, aged 44, postgraduate education, right-

handed male

• Suffered left sylvian stroke involving Wernicke‟s area, the posterior part of the insula, and the inferior part of the supramarginal gyrus(SMG)

• mild conduction aphasia with preserved semantic access

• difficulties of word-form retrieval

• reading and writing from dictation were most impaired, with manyphonological errors

• moderate improvement on follow-up testing

• Token test showed length effect

• 10 age and education-matched controls



Changes in compensatory

activations post-stroke









Thank you!

[email protected]

http://www.tc.edu/neurocog

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A Neurolinguistic Introduction to Aphasia