Transcript Neurological Basis of Language

Some notes
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Room Change (as of Thursday)
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Geological Sciences 135
6339 Stores Rd
Course website
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http://www.psych.ubc.ca/~whitney
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New course outline (corrected formatting)
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Missing page in Dronkers, Redfern & Knight
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Questions for Thursday
Language & the Brain
Adults
Outline of Lecture
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Language & the brain: a history
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Gall, Broca, Wernicke, Lichtheim
The classical model of aphasia
 Problems with the classical model
 Neuroimaging
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Focus on ERPs
Franz Joseph Gall
(late 1700’s)
Phrenology: the linking of human
characteristics with the relative size
of skull areas
 Believed the language faculty to be
located in the two frontal lobes
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Paul Broca
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(1861, 1865)
Patient “Tan”
Right hemiparesis and loss of speech
 Comprehension okay
 Brain viewed at autopsy
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Tan’s Brain
Paul Broca
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(1861, 1865)
Patient “Tan”
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Lesion site claimed to be in the left
frontal lobe
• Broca’s area
Ignored the other damage
 Concluded (with 5 more similar
patients) that left frontal lobe (in right
handers) that controlled the ability for
speech
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Broca’s Area
Third frontal convolution of the inferior
frontal gyrus
Broca’s Aphasia
Carl Wernicke
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(1874)
2 patients with profound deficits in
comprehension and fluent
incomprehensible speech
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Lesion found in the posterior part of the
superior temporal gyrus
• Posterior to primary auditory cortex
Wernicke’s Area
Posterior part of the superior temporal
gyrus
Carl Wernicke
(1874)
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Wernicke’s area was associated with
the storage of the “auditory memory
for words”
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A distinction is now drawn between
“expressive” aphasia (Broca’s) and
“receptive” aphasia (Wernicke’s)
Wernicke’s Aphasia
Wernicke-Lichtheim Model (1874)
Geschwind (1970, 1985)
Explanation of aphasic syndromes
Geschwind
Conclusion from History of Aphasia
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Until recently, most aphasia studies had only a
weak connection to the brain. The important
fact was that brain damage of some sort could
produce selected loss of function (most
interestingly, double dissociations). So deficit
studies can provide evidence for the neural
organization of language independent of any
evidence for the specific localization of the
damage causing the deficit.
Important Concept
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Double dissociation
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Patient A is okay on task 1 but not on task 2
Patient B in not okay on task 1 but okay on
task 2
The lesion pattern may suggest what neural
structures underlie such a dissociation
Current Status of the Model
Left dominance
 Involvement of Broca’s area
 Involvement of Wernicke’s area
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Introduction to Imaging
ERP: Event-related potentials
 MEG: Magneto-encephalography
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PET: Positron Emission Topography
 fMRI: functional Magnetic Resonance
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Imaging
Positron emission
tomography
(PET)
Hemodynamic
techniques
Functional magnetic
resonance imaging
(fMRI)
Non-invasive
recording from
human brain
(Functional
brain imaging)
Electroencephalography
(EEG)
Electro-magnetic
techniques
Magnetoencephalography
(MEG)
Excellent spatial
resolution (~1-2mm)
Poor temporal
resolution (~1sec)
Poor spatial
resolution (~1cm)
Excellent temporal
resolution (<1msec)
Neuroimaging Methods
Techn.
Variable
Time
resolution
PET
[15-O]
water/rCBF
15sec – 1min
5mm
Multiple runs
fMRI
Blood
oxygenation
A few sec.
2mm
Many runs
ERP
scalp-recorded
electric
potential
1msec
Very coarse
Many trials
A few mm
Many trials/
non-unique
solution
MEG
Magnetic field
1 msec
Spatial
Comments
resolution
PET & fMRI vs. ERP & MEG
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PET & fMRI are indirect measures of
neural activity
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Blood flow increases as activity
increases
ERP & MEG are direct measures of
neural activity
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The activity of groups of neurons can
be picked up directly
Focus on ERPs
ERPs are measured via the online
EEG
 A group of neurons (that are
oriented in the same direction) give
off an electromagnetic energy that
can be measured at the scalp
 Non-invasive
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ERPs: Event-Related Potentials
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This methodology makes use of EEG to
measure event related electrical activity
of the brain over time.
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Timelocking
To do this, a number of electrodes are
placed at various sites on the scalp.
The 10-20 Electrode
Placement System
10-20 vs 10-10 Systems
ERPs: Event-Related Potentials
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Averaging across many trials and
many subjects must occur before a
pattern is seen.
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Averaging is a transformation of your
data - it will change the shape of your
waveforms, flattening anything which is
not time-locked to the event
EEGs and ERPs
Averaging
ERP Components
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Features of waveforms which are
related to experimental events or
conditions
Naming of ERP Components
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Positive  “P” Negative  “N”
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Look for whether negative is plotted up
or down!!!
Naming of ERP Components
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1st, 2nd, or 3rd: “P1”, “P2” or “P3”
Precise latency: “P300”
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Latency of peak or of onset
Topography is important
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Frontal N2, Occipital N2
Inferring Neural Activity
from ERP Components
Amplitude: strength of activity
 Latency: timing of activity
 Topography: location of activity
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Compare these variables across
experimental conditions
2 Language Components
N400
 P600
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The N400
(Kutas & Hillyard, 1980)
The pizza was too hot to ???
eat/drink/cry.
The N400
(Kutas & Hillyard, 1980)
Negative plotted up
The N400
(Kutas & Hillyard, 1980)
Polarity: negative
 Latency: 400ms
 Topography: Full scalp distribution
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Semantic processing
The P600
(Hagoort & Brown, 1999)
The spoilt child
are/is
throwing the toy on the ground.
The P600
(Hagoort & Brown, 1999)
The boiled watering can
smokes/smoke
the telephone in the cat.
The P600
(Hagoort & Brown, 1999)
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A positive deflection in the brain wave that
reaches it maximum at approximately 600ms
after the related event.
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Affected by morpho-syntactic anomalies:
The P600 is larger for ungrammatical sentences.
The P600
(Hagoort & Brown, 1999)
Polarity: positive
 Latency: 600ms
 Topography: Posterior distribution
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Syntactic processing
Relation to Classical Model
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Can these ERP findings tell us
anything about the classical model?
N400 – Semantic processing
 P600 – Syntactic processing
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(Left) Anterior Negativities
LAN
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Occurs within the N400 range
300-500 ms
 But, can be as early as 125 ms
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But, more frontally distributed
 Usually larger over left than right
 The conditions that elicit this are
related to syntactic processing
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LAN & the Classical Model
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Left frontal activations is possibly
related to processing of syntactic
information in Broca’s area.
Second Language (L2)
Processing & ERPs
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Comparing native speakers to adult
second language learners.
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What are some of the possibilities?
L2 Grammatical Gender
(Sabourin, 2003)
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Research questions
1.
2.
How do L2 speakers process
grammatical gender information?
Is there an effect of native language
on this processing?