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Abstract:
Abstract: Discrepancies in the patterns of cortical
activation across studies may be attributable, in part, to
differences in baseline tasks, and hence, to the limits of the
subtractive logic underlying much of neuroimaging. To assess these
effects, three of the most commonly used baseline conditions (rest,
tone monitoring and passive listening) were compared with a phoneme
discrimination task, involving eight participants in a fMRI study
with a 4.1 T system. The baselines systematically affected the
amount of activation in the phoneme task within Broca's area, the
left inferior superior temporal gyrus, and the left and right
inferior parietal regions. Two central findings were: (1) a linear
trend in the number of activated voxels for each region, with the
rest condition producing the greatest amount of activation and the
passive listening condition producing the least, and (2) systematic
deactivation in the inferior parietal regions related to the
baseline condition. The decreased activation in Broca's area with
the passive listening baseline compared to the resting baseline
suggests the occurrence of automatic processing. The subtractive
design does not eliminate the necessity of specifying processes
during the baseline condition, even during a rest or passive
baseline condition. The use of graded designs (Sternberg, 1969)
with a common baseline condition may only lessen some of these
interpretive challenges.
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