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Abstract:
Abstract: Distinct prefrontal cortex regions have been
associated with semantic and episodic memory. Semantic tasks have
frequently activated left inferior-prefrontal cortex whereas
episodic retrieval tasks have consistently produced activation in
the right frontopolar region. However, semantic and episodic memory
tasks usually differ with respect to task demands, as revealed by
response latency and accuracy measures. In this study, we
manipulated task demands during a semantic decision task in two
conditions: high-demanding and low-demanding. The task required an
abstract-concrete decision. Task demands were defined according to
the seven-point bipolar scale of Paivio et al. (1968). The
low-demanding condition included words with highly abstract or
concrete scale ratings (1-2 or 6-7) and the high-demanding
condition included words with less extreme
abstractness-concreteness scale rating (2.5-3.5 and 4.5-5.5). When
the semantic task (the two conditions combined) was compared to
baseline (ascending-descending judgment as to the alphabetical
order of the first and last letters of a word), activations in the
left inferior-prefrontal cortex (BA47/45) and the right frontopolar
cortex (BA10) were observed. Direct comparison of the high-
relative to the low-demanding condition revealed no difference in
left inferior-prefrontal cortex, but greater activation in right
frontopolar cortex. These results suggest that activations in right
frontopolar cortex are not specific to episodic memory retrieval,
but may instead be related to the greater reflection associated
with more demanding cognitive judgments.
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