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Abstract:
We investigated neural activity related to retrieval of
context for temporal information during a recency discrimination
task. Subjects first studied two consecutively presented word
lists. At test, event-related brain potentials (ERPs) were recorded
as participants saw pairs of words, and judged which word had been
presented most recently. The test pairs were composed of two
previously studied words, one drawn from each list, (Old+Old
different pairs), both drawn from the same list, (Old+Old same
pairs), or two previously unstudied words (New+New pairs). At
electrode sites overlying prefrontal and temporo-parietal cortex,
ERPs to Old+Old same and different pairs attracting correct recency
judgements were more positive-going than those to New+New pairs.
While there was no difference of this so called old/new effect in
magnitude over frontal electrode sites, it was larger and more
widespread for Old+Old same than for Old+Old different pairs over
left temporo-parietal sites. The frontal and the temporoparietal
old/new effects had more or less parallel time-courses suggesting
that judgements of relative recency involve a simultaneous
processing in the underlying regions. Our findings suggest that the
left temporoparietal old/new effect may index medial temporal lobe
activity engaged in restoration of item and context information
which varied according to the amount of retrieved information. The
frontal old/new effect seemed not to be influenced by the amount of
information and thus may reflect task related working memory
operations mediated by the PFC.
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