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Evidence-Based Complementary and Alternative Medicine
Volume 2012 (2012), Article ID 467061, 22 pages
http://dx.doi.org/10.1155/2012/467061
Research Article

Impact of Global Normalization in fMRI Acupuncture Studies

1Life Sciences Research Center, School of Life Sciences and Technology, Xidian University, Xi’an, Shaanxi 710071, China
2Huaxi MR Research Center (HMRRC), Department of Radiology, West China Hospital, Sichuan University, Sichuan 610041, China
3Institute of Automation, Chinese Academy of Sciences, Beijing 100190, China

Received 9 July 2012; Accepted 9 September 2012

Academic Editor: Ke Ren

Copyright © 2012 Jinbo Sun et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Global normalization is often used as a preprocessing step for dispelling the “nuisance effects.” However, it has been shown in cognitive and emotion tasks that this preprocessing step might greatly distort statistical results when the orthogonality assumption of global normalization is violated. The present study examines this issue in fMRI acupuncture studies. Thirty healthy subjects were recruited to evaluate the impacts of the global normalization on the BOLD responses evoked by acupuncture stimulation during De-qi sensation and tactile stimulation during nonpainful sensations. To this end, we compared results by conducting global normalization (PSGS) and not conducting global normalization (NO PSGS) based on a proportional scaling model. The orthogonality assumption of global normalization was violated, and significant changes between BOLD responses for NO PSGS and PSGS were shown in most subjects. Extensive deactivations of acupuncture in fMRI were the non-specifically pernicious consequences of global normalization. The central responses of acupuncture during De-qi are non-specifically activation-dominant at the somatosensory-related brain network, whose statistical power is specifically enhanced by PSGS. In conclusion, PSGS should be unjustified for acupuncture studies in fMRI. The differences including the global normalization or not may partly contribute to conflicting results and interpretations in previous fMRI acupuncture studies.