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Abstract:
Sentence comprehension declines with age, but the neural
basis for these age-related changes is debated. We compared
cortical activation with BOLD-fMRI during sentence comprehension in
accuracy-matched younger (n=15; age=22.1 yr; 95% correct) and older
(n=11; age=63.5 yr; 91% correct) right-handed English-speakers.
Subjects identified the agent of the action in sentences
manipulating grammatical demands (subject-relative vs.
object-relative center-embedded subordinate clauses) and short-term
memory (STM) demands (3-word vs. 7-word antecedent noun-gap
linkages). Younger and older subjects significantly recruited left
posterior-superior temporal cortex (PSTC) and left premotor cortex
during all types of sentences, and left posterior-inferior frontal
cortex (PIFC) during object-relative sentences with a long linkage.
Younger subjects activated right PSTC during long antecedent-gap
sentences, but older subjects activated right PSTC during all types
of sentences. Direct contrast of age-defined groups also revealed
greater activation in other STM-related regions in older subjects,
including left premotor, left parietal, and bilateral
anterior-inferior frontal cortex in long linkage sentences. These
findings distinguish between a network of age-independent brain
regions supporting core aspects of sentence comprehension, and
age-related brain regions supporting STM during sentence
comprehension.
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