Language - McCausland Center | Brain Imaging

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Language
• Chris Rorden
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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.
3
Language
Distinctly human?
Superior to other animals
Is there a single anatomical basis?
4
Language Production
Broca’s Area (1861)
Difficulty in speech production
Loss of ability to repeat speech
Comprehension intact
Foot 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)
Concepts
(Distributed)
Broca’s
Aphasia
Wernicke’s
Aphasia
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.
Actual location of
BA44/45 based on
histology for two
people. Very
different
size/location
(Amunts et al., 2004
NeuroImage 22, 42-).
Textbook Location of Broca’s Area
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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 nonspeech 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)
Concepts
(Distributed)
Broca’s
Aphasia
Wernicke’s
Aphasia
Conduction
aphasia
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Aphasia Notes [lcbr.ss.uci.edu]
Type of
Aphasia
Broca's
Site of Brain
Damage
Broca's area
Comprehension
Speech
Repetition
Paraphasias
Good
Non-fluent, effortful,
usually agrammatic
Poor
Yes (phonemic,
semantic)
Wernicke's
Posterior STG
Poor
Fluent,
(para)grammatical,
sometimes jargon-like
Poor
Yes (phonemic,
semantic, neologistic)
Conduction
Supramarginal
Gyrus or auditory
cortex
Good
Fluent, grammatical,
self-corrective
Poor
Yes (phonemic)
Global
All of Perisylvian
Cortex
Frontal lobe
Poor
Very little
Poor
n/a
Good
Terse, echolalic
Good
Temporaloccipital-parietal
junction
Poor
Fluent, grammatical,
sometimes jargon-like
Good
Yes (phonemic,
semantic)
Yes (mostly semantic)
Varied, but inf.
temporal lobe
often involved
Lower motor
cortex
Usually auditory
cortex bilaterally
Good
Fluent, Grammatical
Good
No
Good
Dysarthric
Good
No
Very Poor
Fluent
Very Poor
In theory, no, but most
have paraphasias
Transcortical
Motor
Transcortical
Sensory
Anomic
Aphemia
Pure Word
Deafness
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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 callosum
2. 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 (LparietalRparietal, Lfrontal-Rfrontal)
– Also Heterotopic: connecting different regions (LfrontalRparietal).
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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’
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