Subtle Physiologic Rate Differences Affect Group fMRI Studies

Erik B. Beall¹, Lael Stone², Robert J. Fox², Michael D. Phillips¹, Mark J. Lowe¹

Various preprocessing steps have been shown to affect results of fMRI group analyses, however physiologic noise correction is commonly assumed to have little or no effect due to the orthogonality between pulse/respiration and experimental paradigm. Certain populations have systematically different pulse/respiration rates than the general population, and it is possible that this will affect noise variance, thereby affecting activation statistics. We show in a group analysis of Multiple Sclerosis patients that this is indeed the case, and that group analyses comparing populations with subtly different rates must take physiologic noise into account to avoid biased results.