Additional evidence for the sustained effect of acupuncture at the vision-related acupuncture point, GB37.

OBJECTIVE To investigate the dynamics underlying the sustained effect of acupuncture as a possible explanation of earlier findings that acupuncture stimulation at the vision-related acupuncture point, GB37, cannot specifically change the functional MRI (fMRI) signals of the visual cortex compared with stimulation at an adjacent non-meridian point. METHODS The 'on-off' experimental design was separated into four series conditions: 1 min of baseline scanning at the beginning, then two stimulation epochs separated by a 50 s 'rest' period, and then a 1 min 'rest' epoch. The standard General Linear Model (GLM) approach and multi-conditions analysis were used. RESULTS Results from the multi-conditions analysis were different from those from the standard GLM analysis. We found that the neural signal of the limbic-paralimbic-neocortical system after acupuncture stimulus lasted longer than the putative period. Furthermore, the fMRI signal changes in the occipital cortex showed different temporal patterns between GB37 and the non-meridian point. CONCLUSIONS Owing to the sustained effect of acupuncture, standard GLM analysis may be unsuitable for 'on-off' design acupuncture studies and lead to uncertain and contradictory results. The findings from this study suggest that acupuncture at GB37 can induce complex brain activity in the vision cortex. The state-related neural signal may reflect one of the significant characteristics underlying acupuncture.