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Abstract:
Recent neuroimaging studies have revealed anterior prefrontal
activations during verbal working memory performance, particularly
in high memory demand conditions and under articulatory
suppression. In the present study, we attempted to further specify
the functional contribution of anterior prefrontal cortices to
phonological short-term memory by parametric variations of these
two factors (memory load and articulatory suppression rate).
Fifteen healthy right-handed volunteers underwent functional
magnetic resonance imaging (fMRI) at 3 Tesla (Bruker Medspec
30/100). Gradient echo-planar image series (TR=1.5s, TE=40ms,
FA=90°, voxel size=3x3x5mm3) were obtained in 18 slices
covering the entire cerebrum. Subjects performed a Sternberg task
requiring phonological maintenance of verbal items. Different
memory load and articulatory suppression conditions were arranged
in a bifactorial manner. We observed activations related to verbal
rehearsal in left premotor cortices including Brocas area, in the
left intraparietal sulcus and right cerebellum. Additionally,
bilateral activation of the anterior middle frontal gyrus was found
both in the highest memory load condition without suppression and
(to a comparable extent and at nearly identical location) in lower
memory load conditions under articulatory suppression. While this
pattern of occurrence cannot be fully explained by the actual
memory demands, the findings suggest that the anterior middle
frontal gyrus participates in phonological storage whenever the
capacity of mechanisms that commonly underlie articulations and
rehearsal is exceeded.
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