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Abstract:
he 'event-related' fMRI design has proven as powerful as the
classic 'blocked' design for cognitive research, and it provides
crucial information on the timing of the brain events that follow
presentation of an isolated stimulus. We adapted this design to
imaging of auditory cortex function. Five subjects were scanned on
a 1.5T Siemens Vision imager. Functional volumes were 10 contiguous
axial T2* gradient echo EPI images (head coil, 5mm thick, TR/TE/FA:
20sec/50msec/90, matrix size: 64x64). T1-weighted 3D volumes were
acquired for anatomical localization (1mm thick, matrix
size:256x256). In order to minimize the influence of the EPI image
acquisition acoustic noise artifact on auditory cortex activity, a
very long repetition time (TR=10 sec) was used. 128 functional
volumes were acquired, for a total scanning time of 21 min. A
single auditory stimulus was presented at variable delays before
each image acquisition (1 to 9 sec). Images were smoothed and
corrected for motion using in-house dedicated software. In primary
and secondary regions of auditory cortex, voxels with maximum BOLD
signal difference between baseline and max of delays 3, 4 and 5 sec
were identified, and their BOLD time-course reconstructed. Average
BOLD time-course in the five subjects yielded curves very similar
to those already obtained in the visual cortex, but with BOLD
maxima attained significantly earlier, at delays 3 to 4 sec
depending on cortical position.
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