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Abstract:
In previous imaging studies, we found activations of
Brodmann's Area (BA) 22/42 and BA44/45 in auditory phoneme
monitoring tasks. Here, we complement earlier results with
Event-Related fMRI to relate locations of activations with temporal
information. Seven subjects underwent fMRI sessions (EPI 1,5 T)
while performing two tasks: (a) silent repetition of pseudo-word
pairs as soon as possible after stimulus onset and (b) sequential
detection of a /b/ in a pseudo-word when /d/ is present in the
preceding pseudo-word. Fourteen Stimuli were delivered every 18
seconds in 4 runs and 6 slices were acquired every 2 s. (lower
slice across AC-PC, thickness 6mm). After normalization into
Talairach Atlas and realignment, activations were detected with
SPM96 at p<0.01. After convoluted signals were averaged and
splined, activated voxels were coded according to maxima latencies
of corresponding Event-Related Hemodynamic Responses. The following
spatial-temporal sequence was observed in both tasks: (1) primary
auditory cortex (BA41) bilaterally, and Thalami, (2) right BA31 and
BA22/42 bilaterally, (3) BA44/45 bilaterally, left BA39/40, BA23
and BA6 bilaterally. The left BA39 was more activated in the
detection task. Event-Related fMRI gives access to both spatial and
temporal information on cognitive processes such as language. Our
results support the hypothesis that BA44/45 (Broca's area), BA23/31
(Posterior Cingular Gyrus) and BA39/40 (Supramarginal and Angular
Gyri) are part of a rehearsal system maintaining linguistic
material in working memory.
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