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Abstract:
Goldman-Rakic and Fuster both offer a conceptualization of
working memory that emphasizes how prefrontal and posterior
cortical areas are linked in reverberatory circuits that keep
information on line. Goldman-Rakic argues that these working memory
circuits are modality-specific, with dorsal PFC and parietal
activation for spatial processing, and ventral PFC and inferior
temporal activation when non-spatial or pattern information is key.
Cohen (1997) demonstrated fMRI activation of the dorsolateral PFC
as a function of load in an n-back working memory task. We employed
a similar task to test the modality-specific working memory model
using electrophysiological measures, with a spatial condition
(position being the matching criterion of letter stimuli presented
either 1, 2, or 3 items earlier) and a verbal condition (specific
letter to be matched). ERPs to stimuli were recorded from 9 frontal
and 9 parietal coronal sites from the extended 10-20 system. P300
analysis indicated no modality-specific differences in the
dorsal-ventral plane, although P300 latencies and amplitudes were
greater for verbal stimuli, increasing as a function of working
memory load. P300 amplitudes were significantly greater at the
dorsal sites. Such results accords with fMRI results of increased
dorsolateral PFC activation with working memory.
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