Evaluation of group homogeneity during acupuncture stimulation in fMRI studies

Purpose: To evaluate the extent of individual differences of functional MRI (fMRI) signal changes induced by acupuncture stimulation. Materials and Methods: Acupuncture at ST36 and checkerboard stimulation was applied to 16 subjects. We calculated the mean distance using beta values in a generalized linear model (GLM) analysis and employed it to study the group homogeneity by detecting the outliers. Results: A more significant individual difference was presented in acupuncture stimulation compared with visual stimulation through evaluation of the mean distance. From the group results, we found that the activations were more significant in the homogeneous group results. Combining the behavior and fMRI results, there was no direct correlation between deqi index and mean distance in acupuncture stimulation. The deqi index of the outlier was in the normal range and did not differ significantly from others. Conclusion: Traditional group results without removing outliers were not sensitive enough to detect the real acupuncture effect. We suggest that individual difference should be taken into consideration for future acupuncture studies. Also, group analysis paralleled with individual analysis is critical for a full understanding of acupuncture effects.