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Language

• Chris Rorden• Aphasia: Broca’s, Wernicke’s, etc.• Alexia• Anomia• Dyslexia• Agraphia• Split brain patients• Disconnection syndromes

www.mricro.com

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Background (from c82bio)

Localization– Certain regions devoted to

specific tasks.– Broca, Gall– Based on (almost) no evidence

Equipotentiality– Whole brain involved with tasks– Flourens (1840s), Head, Lashley

Both correct/wrong.

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Language

Distinctly human?

Superior to other animals

Is there a single anatomical basis?

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Language Production

Broca’s Area (1861)Difficulty in speech productionLoss of ability to repeat speechComprehension intactFoot of 3rd frontal convolution

(BA 44)Left hemisphere (1865)

– Except left handers

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Language Comprehension

Wernicke’s Area (1874) Normal production (speech sounds and

fluent nonsense) Sounds okay if you do not know the

patient’s language (e.g. Chinese Wernicke’s aphasic would sound fine to me)

Unaware of deficit Impaired comprehension Left hemisphere Superior temporal gyrus

(BA 42, 22)

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Wernicke’s prediction

Predicted two language centers:– Broca’s Area: speech articulation.– Wernicke’s Area: language comprehension.

Predicted 3rd Syndrome:– Disconnection syndrome– ‘Conduction aphasia’– Damage to

arcuate fasciculus

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Conduction aphasia

Can comprehend speech Articulation is intact Difficulty in repeating speech Lesions in Temporal Parietal Junction that

knock out underlying white matter Patients with damage ONLY to the arcuate

fasciculus can still generate speech.– Why? Other pathways

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Wernicke-Lichtheim (1885) Schema

From auditory input (a) to motoric articulation of speech (m)

Broca’s Aphasia Wernicke’s

Aphasia

Concepts(Distributed)

Conduction aphasia

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4: Transcortical Motor Aphasia

Disconnection of Broca’s from concepts

Speech is slow, terse Can comprehend speech Found after damage to the

frontal lobes Unlike Broca’s Aphasics,

can repeat phrases when spoken to– direct Wernicke’s to Broca’s

pathway intact

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6: Transcortical Sensory Aphasia

Disconnection of Wernicke’s from concepts

Can repeat words Speech is articulate

nonsense Unable to comprehend

speech Found after damage to the

posterior language area

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7 Pure Word Deafness

Loss of ability to understand spoken speech.

Normal speech, reading, writing

Behaviour and anatomy dissociate from Wernicke’s aphasia

Written comprehension intact, intact written/verbal production.

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Specifically language

Aphasics unable to use speech to convey information.

However, aphasics can often cite memorized texts– Songs– Prayers, verses– Cliché

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Exceptions to the rule

Dronkers et al [2000] note exceptions to anatomy Traditional Theory:

– JC will have Broca’s and MC will have Wernicke’s Aphasia– JH and OB will not have aphasia

Reality: – Neither JC or MC has Aphasia– JH has Broca’s and OB has Wernicke’s Aphasia.

Broca’s Wernicke’s

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Exceptions to the rule

Patients with similar lesions can show very different behaviour.

What are the implications?

Are these exceptions to rule worth worrying about?– Perhaps we can not see functional extent of OB/JHs lesion

But JC/MC clearly have damage in areas associated with language deficits.

– Different brains develop differently– Group studies required

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Brain areas vary between people

Broca’s Area = Brodmann’s 44/45 BA44/45 vary between people Perhaps Broca was right, but JC and JH have slightly

unusual locations for these regions. Group studies required to resolve this question.

Textbook Location of Broca’s Area

Actual location of BA44/45 based on histology for two people. Very different size/location

(Amunts et al., 2004 NeuroImage 22, 42-).

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Broca’s Aphasia

Broca’s Aphasia is a syndrome: association of deficits. – ‘Telegraphic’ speech: Produce content words with few

grammatical markers, pauses between words– Apraxia of Speech: distortion of speech sounds

(‘yawyer’ instead of lawyer), poor prosody, stress on wrong syllable without motor problems for non-speech movements.

– Dysarthria: poor control of muscles used in articulation– Word finding– Repetition– Comprehension: problems with complex grammar.

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Problems with traditional model

Does this cluster of symptoms reflect one functional module, or separate anatomical neighbours?

Comprehension: Broca’s not simply problem in speech production– Intact: ‘the boy kissed the girl’– Problems: ‘the girl was kissed by the boy’

Is comprehension specific to speech, or due to attentional/working memory problems?

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Fractionation of Broca’s Aphasia

Dronkers et al (1994) examined > 100 aphasics Comprehension deficits associated with Broca’s Aphasia

appear to correlate with Temporal Lobe damage. Suggests association due to neighbouring centers, not

shared function. Finding confirmed in neuroimaging studies (Bavelier et al.

1997).

Broca’s Area (BA44/45)

Region identified by Dronkers

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Reflections

Dronkers suggests grammatical problems not due to Broca’s Area

Used low quality structural scans – See Hillis et al. for critique. Brain (2004),

127, 1479-1487

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Apraxia of Speech

Dronker’s [1996, Nature, 384, 159-161] AoS: disorder of shaping the vocal tract for a particular

speech sound. Studied 25 apraxic and 19 control patients.

– Tested 1 year after lesion: deficits are stable.– All AoS had damage to portion of insula.– This region was spared in all controls.– Region near motor strip [M1] for mouth.

Apraxics Controls

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Apraxia of Speech

Dronkers (1996) suggest that insular damage causes AoS.

– Supported by Shuren,, 1993; Donnan et al., 1997; Bates et al., 2003).

Hillis et al. (2004; Brain 127 1479-1487) disagree: argue Broca’s Area critical for AoS.

– Dronker’s examined chronic patients with structural scans.

– Hillis examined acute patients and found that patients with AoS had perfusion deficits in Broca’s Area, even if these were not seen in structural scans.

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Wernicke-Lichtheim (1885) Schema

From auditory input (a) to motoric articulation of speech (m)

Broca’s Aphasia Wernicke’s

Aphasia

Concepts(Distributed)

Conduction aphasia

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Aphasia Notes [lcbr.ss.uci.edu] 

Type of Aphasia

Site of Brain Damage

Comprehension Speech Repetition Paraphasias

Broca's Broca's area Good Non-fluent, effortful, usually agram m atic

Poor Yes (phonem ic, sem antic)

Wernicke's Pos terior STG Poor Fluent, (para)gram m atical,

som etim es jargon-like

Poor Yes (phonem ic, sem antic, neologis tic)

Conduction Supram arginal Gyrus or auditory

cortex

Good Fluent, gram m atical, self-corrective

Poor Yes (phonem ic)

Global All of Perisylvian Cortex

Poor Very little Poor n/a

Transcortical Motor

Frontal lobe Good Terse, echolalic Good Yes (phonem ic, sem antic)

Transcortical Sensory

Tem poral-occipital-parietal

junction

Poor Fluent, gram m atical, som etim es jargon-like

Good Yes (m os tly sem antic)

Anom ic Varied, but inf. tem poral lobe often involved

Good Fluent, Gram m atical Good No

Aphem ia Lower m otor cortex

Good Dysarthric Good No

Pure Word Deafness

Usually auditory cortex bilaterally

Very Poor Fluent Very Poor In theory, no, but m os t have paraphas ias

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Aphasia notes

Anomic: problem naming objects Paraphasia: use of related but inappropriate words

– Semantic: ‘fork’ when ‘knife’ is meant– Phonemic: ‘fork’ when ‘stork’ is meant

Neologism: literally “new word,” using word that bears no obvious relation to a recognizable word. e.g., “glester”

Paragrammatic: incorrect use of grammatical function words. e.g., “he is always brillianting”

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Recovery from aphasia

Many aphasics get better– Is this due to intact tissue on damaged left?– Or does right hemisphere take over?

Warburton et al. (1999) examined recovered aphasics.– Many controls show left-only activity [far left]– Others show bilateral activity, but predominantly left [2nd

from left]– Patients show different patterns of activity: for some,

intact regions on damaged side have become active.

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Musical Syntax

Musical syntax is processed in Broca's area.

Non-musicians listen to 5 chords harmonically inappropriate chords

generate early right-anterior negativity (ERAN), measured with MEG.

Inferior BA44 source of ERAN (Broca’s source and right homologue).

Maess et al. (2001) Nature Neuroscience 4, 540 – 545.

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Reading and writing

Wernicke’s aphasics: language comprehension– Regardless whether spoken or written

Broca’s aphasics: speech production– Primarily spoken (except grammar)

Are there specific reading centres?

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Alexia with agraphia

Déjerine, 1891: Damage to the angular gyrus (BA 39) leads to– ‘Alexia with agraphia’ reading & writing

deficits– Intact speech comprehension

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Alexia without agraphia

Disconnection of angular gyrus from visual inputs– Language outputs intact– Patients cannot read– Writing preserved

Rare: left and right pathways to angular gyrus

Requires damage to 1. posterior callosum2. left occipital lobe

Without damage to left angular gyrus

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Reading Vision vs Braille

Fusiform gyrus also involved with reading

Büchel et al. (1998) Nature, 394, 274-277.– 3 Groups:

Sighted Early Blind Congenitally Blind

– Reading activates fusiform gyrus (relative to speech).

– Fusiform not simply visual area.

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Language and laterality

Language mainly LEFT hemisphere task– Broca’s/Wernicke’s patients left

hemisphere– Wada Test [Intracarotid amobarbital

procedure] temporarily disables one hemisphere

Virtually all right handers have language in left Left Handers:

– 70% like right handers– 15% language on right (reversed)– 15% distributed language (bilateral)

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Brain asymmetries (Toga & Thompson, 2003)

Right frontal and left occipital protrude relative to counterpart

Skull imprints called ‘petalia’ Cortical structures (sulci)

shifted as well (‘Yakovlevian torque’)

Cortical Assymetries Left occipital: wider, protrudes posteriorly Right frontal: wider, protrudes anteriorly

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Brain asymmetries

Sylvian fissure (SF) and superior temporal sulcus (STS) also differ between left and right.

Left SF/STS more posterior Planum temporale (posterior-ventral face of

STS) larger on left. See Martin’s Human Neuropsychology for more asymmetries.

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Corpus callosum

Fiber tract between left and right side of the brain.– 200 million axons– Primarily homotopic: connects corresponding region

(Lparietal-Rparietal, Lfrontal-Rfrontal)– Also Heterotopic: connecting different regions (Lfrontal-

Rparietal).

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Split brain patients

Complete or partial commissurotomy – 1950s operation for intractable epileptics – Unseen objects

Identified when presented to right hand Verbally unidentified when presented to left hand, though

hand can select matching object

– Visual stimuli (briefly flashed) Verbally describe items presented to right field Unable to name items in left field, though can choose

correct item with left hand

– Spatial tasks: suggest right hemisphere better (Nebes, 1978).

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Alien Hand Syndrome

Alien hand syndrome [Brion and Jedynak; 1972]– Split brain patients do not recognize their unseen left

hand when touched by right hand.– ‘intramanual conflict’: e.g. one hand buttons up shirt,

other unbuttons.– Left hand spontaneously engages in actions that the

patient says they are not intending: acts foreign, alien or uncooperative.

– Seen in other patients: Goldberg et al (1981) report similar effects in patients with mesial-frontal/callosal lesions

– AKA ‘wayward hand’, ‘anarchic hand’