Last Lecture




Dichotic Listening
The corpus callosum &
resource allocation
Handedness
Broca’s Aphasia
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
This Lecture




Wernicke’s aphasia
The Wernicke-Geschwind Model
Category-specific semantic deficits
and the representation of meaning
Introduction to the Frontal Lobes
Remember the Wernicke-Geschwind
model?


Broca’s area: forms detailed
coordinated plans for language
production (speech, writing,
covert/rehearsal)
Explains dysfluency and poor
articulation in Broca's aphasics.
But comprehension is not
perfect...


Poor syntax comprehension
Broca's aphasics poor at judging
grammaticality
Active: The horse
kicked the cow.
Passive: The cow was
kicked by the horse.
Agrammatism


Disproportional difficulty reading and producing
function words.
Difficulty using & understanding grammar
Modification to Wernicke-Geschwind model
Broca's area:
 Plan for coordinating language production
 Understanding and using syntax.
Wernicke's aphasia
Examiner: Can you tell me a little bit about why
you’re here?
Patient: Sine just don’t know why, what is really
wrong, I don’t know, cause I can eaten treffren
eatly an everythin like that I’m all right at
home.
(Excerpt from Kertesz, 1980; quoted by Carlson, 1994)
Symptoms of Wernicke's
aphasia







Speech: phonetically & grammatically normal but
meaningless.
generally fluent, unlabored, well articulated.
normal intonation (prosody).
words used inappropriately
nonsense words (neologisms) --> "word salad"
meaning expressed in roundabout way
(circumlocution).
Comprehension: severely impaired.
According to Wernicke-Geschwind
model
Wernicke's Area ...



DOES NOT STORE MEANING!
stores memories of sound sequences that
constitute words.
translates auditory input into phonological forms
that can then access semantics.
Interpretation of Wernicke's area in
action
Understanding spoken language:

Primary auditory cortex ( 41/42) -> Wernicke's A. (22) -> semantic
networks distributed throughout the brain.
Spontaneous speech: "cognitive" areas send input to
Wernicke's area:

Cognition -> Wernicke's A. (22) -> arcuate fasciculus -> Broca's A.
(44)-> Primary motor cortex
PET activation during listening
ickTi me™ and a
JPEG decompressor
d to see this picture.
According to the Wernicke-Geschwind
model...
Wernicke’s A. essential for reading...
Visual processing --> Angular g. --> Wernicke's a.-->
Semantics

Angular gyrus (39) translates visual code to a form accessible by
Wernicke’s a.

grapheme --> phoneme translation

Wernicke’s a. translates to a form that can access meaning.

Implication: Reading requires phonological recoding via
Wernicke’s A.
Where is meaning stored?

Wernicke’s area does not store meaning, so
where is it stored?

Meaning is represented across a network of
brain areas

Different brain areas contribute to different kinds of
knowledge
How do we know this?
Loss of SEMANTIC KNOWLEDGE:

can’t recognize, describe from memory, or answer questions
about objects.
Category -specific deficits:


Some patients cannot recognize living things (plants/animals) but
can recognize man-made things (tools/instruments)
Opposite pattern also reported (non-living things-impairment)
Double dissociation: separable representations for difference
categories of knowledge.
PET evidence: Category-specific
activations (Martin et al., 1996)



Subjects identified pictures of animals and tools
Certain visual areas more active for animals
Left premotor area more active for tools.
Semantic representation:
- tools represented by function.
- living things represented by visual/sensory features.
The Role of Language

Language ability sets us apart from other
animals.

Is language what makes us uniquely human?
Phineas Gage

Railroad worker who
experienced head trauma.

He survived.
Drastically changed his
personality.


“Gage was no longer Gage,”
according to his friends.
The Frontal Lobes
Claim: The frontal lobes mediate those
abilities that make us uniquely human.

Herein lies the riddle... What makes us
uniquely human?
The Frontal Lobes

3 natural boundaries



posterior: central sulcus
inferior: Sylvian fissure (lateral fissure)
medial/inferior: corpus callosum
Major Subdivisions
Precentral (motor cortex): Area 4
Premotor:


Areas 6 and 8 (including
supplementary motor)
44 (Broca’s area)
Prefrontal:



dorsolateral: Areas 46, 45, 9, 10
ventrolateral: Areas 11, 47
orbital: 11
Anterior Cingulate:

medial: Areas 24, 25, 32