Download Cortical activation and synchronization during sentence

Cortical activation and
synchronization during sentence
comprehension in high-functioning
autism: evidence of underconnectivity
Marcel Adam Just, Vladimir L. Cherkassky,
Timothy A. Keller ans Nancy J. Minshew
Brain, 127: 1811-1821, 2004
Introduction of autism
•
Named by Dr. Leo Kanner in 1943
–
•
A population of individuals who were very isolated
and aloof. Autism means “self”
Autism is a syndrome disorder. It has four
diagnostic criteria which must be present:
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–
–
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Impairment in social interaction
Impairment in communication
Restricted, repetitive stereotyped patterns of
behavior
Onset prior to age three
Introduction of autism (con’t)
• The symptoms of autism occur on a
continuum from mild to severe
– Diagnostic subgroups of autism
High IQ
60
Low IQ
Fluent/Verbal speech
Nonverbal
high-functioning
II
III
IV
Dr. Temple Grandin
http://www.grandin.com/
– B.A. (Psychology), Franklin
Pierce College, 1970.
– M.S. (Animal Science), Arizona
State University (part time),
1975.
– Ph.D. (Animal Science),
University of Illinois (part time),
1989.
Language processing areas
Left inferior frontal gyrus
Left superior and
middle temporal gyrus
Broca’s aphasia (agrammatic aphasia)
– "Yes... ah... Monday... er... Dad and Peter H... (his
own name), and Dad.... er... hospital... and ah...
Wednesday... Wednesday, nine o'clock... and oh...
Thursday... ten o'clock, ah doctors... two... an'
doctors... and er... teeth... yah."
Wernicke’s aphasia (fluent aphasia)
– "I called my mother on the television and did not
understand the door. It was too breakfast, but they
came from far to near. My mother is not too old for me
to be young.
Language processing areas
Syntactic processing
Semantic processing
Working memory functions
Left inferior frontal gyrus
Lexical processing
Left superior and
middle temporal gyrus
Previous study of high-functioning autism
• A preserved or even enhanced ability in the narrowerscope task of reading individual words. A deficit in the
broader-scope task of processing grammatically
(Goldstein et al, 1994)
• Brain activation in Broca’s area and Wernicke’s area
may play a central role in accounting for the language
comprehension abnormalities in autism
– PET study: less lateralization in the perisylvian and temporal
areas in autism (Muller el al, 1999)
– Morphometric study: Broca’s and Wernicke’s areas of left
hemisphere are smaller than the homologue of right hemisphere
in autism (Herbert et al, 2002)
Methods
• Group matching:
– 17 high-functioning autistic participants
– 17 healthy normal participants (verbal IQmatched)
• Sentence comprehension task
Active sentence
The cook thanked the father. (main sentence)
Who was thanked? (probe)
cook-father
Passive sentence
The editor was saved by the secretary.
Who was saving?
editor-secretary
Active sentences
Passive sentences
5
5
5
5
5
Filled with fixation epochs (24s)
5
5
Behavioural performance
• Reaction time:
autistic
control
active
2456 ms
3061 ms
passive
2803 ms
3447 ms
Autistic group took reliably shorter than control group
F(1,32)=4.36, p<0.05
• Error rates:
autistic
control
active
8%
5%
passive
13%
7%
Autistic group is slightly but not reliably higher than control group
Hypothesis (part I)
• Autistic participants may rely more on an enhanced
word-processing ability and rely less on integrating
processes that bring the words of a sentences together
into an integrated syntactic and semantic structure
• Wernicke’s area
• Broca’s area
• Using fMRI to examine the brain activation
Results
Broca’s area
And adjacent areas
Secondary visual area
Wernicke’s area
Hypothesis (part II)
• Complex cognitive processing (eq. language processing)
needs large-scale cortical networks to collaborate. The
activation in a set of cortical areas should be
synchronized, indicating collaboration among areas
• Synchronization: compute the correlation or covariance
between activation levels in two activated areas
• Synchronization is taken as evidence of “functional
connectivity”
• Underconnectivity: lower level of functional connectivity
among autism
Results
Result
Conclusions
• The autism group perform the task faster and
less accurately
• The autism group produced reliably more
activation than the control group in Wernicke’s
area
• The autism group produce reliably less
activation than the control group in Broca’s area
• The functional connectivity was consistently
lower for the autistic than the control participants
Discussion
• The higher brain activation in Wernicke’s area is consistent with their
hyperlexicality or unusual strength in processing single words
• The lower brain activation in Broca’s area is consistent with the
finding that high-functioning autism are impaired in their ability to
process the meaning of complex sentences
– The lower activation of secondary visual cortex may also be consistent
with this account. The use of mental imagery might be another way to
form an integration of the meaning of a sentence
• Underconnectivity is unlikely to be specific to language. It is also
shown in non-language task. Any facet that is dependent on the
coordination or integration of brain regions is susceptible to
disruption in autism, particularly when the computational demand of
the coordination is large.
• Underconnectivity vs weak central coherence theory (Frith, 1989)