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Abstract:
Abstract: Neuroimaging studies have used two approaches to
identify neural correlates of memory encoding. Haemodynamic studies
have typically contrasted items that are either semantically or
perceptually processed. Electrophysiological studies have
contrasted individual items according to whether the items are
subsequently remembered. Here, we directly compared these
approaches using procedurally equivalent event-related fMRI and ERP
experiments. At study, participants were cued to make either
animacy or alphabetical decisions about words. A recognition memory
test followed after a delay of at least 20 min. Prefrontal and
medial temporal regions showed greater fMRI activations for
semantically- relative to alphabetically-encoded words. Some of
these regions (left prefrontal cortex and hippocampus) showed
greater activation for semantically processed words that were
subsequently remembered. Successful memory for alphabetically
encoded words was associated solely with left hippocampal
activation. ERPs showed a centroparietal, positive-going modulation
for both semantic encoding and successful memory for semantically
encoded words. Successful memory was also associated with an early
left-frontal modulation in the semantic encoding condition. In the
alphabetic condition, remembered words were associated with a
negative-going modulation. The findings suggest that (a) memory
encoding for semantically processed words involves a subset of the
regions activated by semantic processing per se; (b) the neural
correlates of memory encoding differ qualitatively, rather than
quantitatively, according to whether study is semantic or
nonsemantic.
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