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Abstract:
Phonological working memory tasks activate left frontal and
inferior parietal cortex. Most authors have interpreted the frontal
activations as the neural system supporting articulatory rehearsal,
and the inferior parietal activation as the site of the
phonological store. Hickok and Poeppel (2000, TICS, 4:131-8)
offered another interpretation: parietal activation reflects the
operation of a auditory-motor integration network for speech -- on
analogy to visuo-motor integration networks in superior parietal
regions -- which enables frontal articulatory mechanisms to keep
active sensory-based representations of speech in the posterior
STG. This model predicts activation both in inferior parietal and
posterior STG sites in working memory tasks; the latter has not
been reported previously. We tested this prediction using an
event-related fMRI paradigm in which seven subjects listened to
multisyllabic pseudowords (3 per trial) and then rehearsed them for
27sec (24 trials). Using multiple regression, we identified in each
subject two posterior sites which were activated during both the
auditory and the rehearsal period (p<.0001), as predicted: a
region deep in the Sylvian fissure at the boundary of the parietal
and temporal lobes (Spt), and a more lateroventral STG/STS site.
The precise location of these two sites varied between subjects
such that warped/averaged group analysis obscured these
activations. The timecourse of activation in area Spt was highly
correlated (r=.992) with activation in Broca's area suggesting a
tight functional relation between the two.
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