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Abstract:
Neuroimaging studies have revealed a widely distributed
neural network underlying working memory functions including
cortical as well as subcortical structures. In the present study,
we investigated in more detail the relative functional contribution
of these brain regions to different components of working memory,
i.e. storage and executive processing. Seven healthy right-handed
volunteers underwent functional magnetic resonance imaging (fMRI)
at 3 Tesla (Bruker Medspec 30/100). Gradient echo-planar image
series (repetition time = 2s, echo time = 40ms, flip angle =
90°, voxel size = 3x3x5mm3) were obtained in 16 slices covering
the entire cerebrum. Experimental conditions consisted, firstly, of
a modified digit-ordering task demanding "online"-maintenance as
well as manipulation of relevant information and, secondly, of a
result-matching phase requiring predominantly the maintenance
component of working memory. Thirdly, an appropriate forced-choice
control condition was applied which matched both activation
conditions with respect to visual input and motor output
processing. When contrasting result-matching with the forced-choice
control, averaged group analysis showed significantly increased
brain activity right-accentuated in inferior frontal and posterior
parietal areas. In direct comparison with result-matching,
digit-ordering evoked strong activation in frontal, parietal,
premotor and cerebellar regions which was lateralized to the left
cerebral hemisphere and the right cerebellum. These findings
suggest a functional dissociation of brain structures according to
the respective demands on specific sub-processes of working
memory.
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