A recent paper by Kastrup et al. (abstract attached below) found that
the absolute size of the fMRI response to visual stimulation did not
vary with global blood flow . This seems to suggest that one should use
additive scaling rather than proportional scaling or ANCOVA to get rid
of global effects in fMRI. Any impressions about this?
best,
russ
Relationship between cerebral blood flow changes during visual
stimulation and baseline flow levels investigated with functional MRI
Andreas Kastrup*, Tie-Qiang Li?, Gunnar Krüger?, Gary H. Glover§,
Michael E. Moseley¶
NeuroReport 10:1751-1756
Using fMRI, the relationship between regional cerebral blood flow (rCBF)
changes during visual stimulation and the prevailing baseline global and
regional flow levels was evaluated in 22 volunteers. The absolute
increase in rCBF was not correlated with baseline rCBF values (r = 0.01,
p = 0.8); however, the percentage change in rCBF showed a negative
correlation (r = ?0.78, p < 0.001). Both absolute and relative changes
in rCBF were independent of baseline global CBF
values. These results indicate that caution should be exercised when
comparing relative flow changes during focal brain activation,
especially in functionalneuroimaging studies dealing with altered
baseline flow values. © 1999 Lipponcott Williams & Wilkins
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