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Abstract:
Behavioral research suggests that semantic memory is in many
respects preserved during normal aging, but little is known
regarding the neural systems mediating older adults performance on
semantic tasks. We used positron emission tomography to measure
regional cerebral blood flow (rCBF) during visual word
identification (lexical decision) and a nonsemantic baseline task
(letter search). Participants were 12 younger adults (M = 23 years)
and 12 older adults (M = 65 years). Reaction time was higher
overall for older adults than for younger adults. Changes in
performance as a function of lexical processing, display duration,
and presentation rate were comparable for the two age groups. For
both age groups, the largest clusters of rCBF activation associated
with lexical processing were located in the left hemisphere
(occipitotemporal pathway and inferior prefrontal cortex).
Lexical-related activation decreased with age in the left striate
cortex and right anterior cingulate, but increased with age in the
left inferior temporal cortex and right cerebellum. Normalized
reaction time was correlated positively with rCBF activation of
left striate cortex for younger adults but not for older adults.
These results suggest that although younger and older adults
exhibit qualitatively similar patterns of word identification
performance, functioning of the relevant neural systems does
undergo age-related change.
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