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Randomized Controlled Trial
, 47 (3), 1066-76

An fMRI Study on the Interaction and Dissociation Between Expectation of Pain Relief and Acupuncture Treatment

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Randomized Controlled Trial

An fMRI Study on the Interaction and Dissociation Between Expectation of Pain Relief and Acupuncture Treatment

Jian Kong et al. Neuroimage.

Abstract

It is well established that expectation can significantly modulate pain perception. In this study, we combined an expectancy manipulation model and fMRI to investigate how expectation can modulate acupuncture treatment. Forty-eight subjects completed the study. The analysis on two verum acupuncture groups with different expectancy levels indicates that expectancy can significantly influence acupuncture analgesia for experimental pain. Conditioning positive expectation can amplify acupuncture analgesia as detected by subjective pain sensory rating changes and objective fMRI signal changes in response to calibrated noxious stimuli. Diminished positive expectation appeared to inhibit acupuncture analgesia. This modulation effect is spatially specific, inducing analgesia exclusively in regions of the body where expectation is focused. Thus, expectation should be used as an important covariate in future studies evaluating acupuncture efficacy. In addition, we also observed dissociation between subjective reported analgesia and objective fMRI signal changes to calibrated pain in the analysis across all four groups. We hypothesize that as a peripheral-central modulation, acupuncture needle stimulation may inhibit incoming noxious stimuli; while as a top-down modulation, expectancy (placebo) may work through the emotional circuit.

Figures

Figure 1
Figure 1
Details of experimental procedure. In Session 2, we used a marker to draw a numbered 2 x 3 grid on the medial aspect of the right forearm and placed the thermal probe in one box of the grid for each of the stimulus sequences (e.g. random pain (RP) and identical pain (IP) sequences). After electroacupuncture treatment in high expectancy groups, decreased stimulus temperatures (dIP) indicated by green color were applied on the meridian side (HE side), but not on the non-meridian side (Control side) to give each subject an unmistakable experience of analgesia. After electroacupuncture treatment in low expectancy groups, the same temperature pre-treatment IP stimuli were applied. In Session 3, subjects were told that Session 2 procedures would be repeated during the fMRI scan. However, only one dIP was decreased (green color) on the HE side in high expectancy groups. Original temperatures were administered to the remaining regions of the forearm, thus the pre- minus post- treatment contrast is a subtraction of identical stimuli. The pre- and post- treatment pain ratings and fMRI signal change differences between the meridian side and non-meridian (Control) sides were the primary outcomes of this study.
Figure 2
Figure 2
Subjective sensory pain rating changes (pre- minus post-) on meridian (HE/LE) and Control sides across four groups. VH: verum acupuncture high expectancy group; VL: verum acupuncture low expectancy (VL) group; PH: placebo acupuncture high expectancy group; PL: placebo acupuncture low expectancy group.
Figure 3
Figure 3
Representative brain regions showing significantly greater fMRI signal decrease after verum acupuncture with high expectancy (VH) compared with verum acupuncture with low expectancy treatment (VL) on meridian side (VH > VL). The bars indicate averaged beta values (3 mm sphere around the activation peak) of pre- and post-treatment difference in VH group (dark) and VL group (grey) for each of the brain regions indicated on the accompanying image (mean ± SE). L indicates left side of the brain, rACC: rostral anterior cingulate cortex; MPFC: medial prefrontal cortex; OPFC: orbital prefrontal cortex.
Figure 4
Figure 4
Representative brain regions involved in expectancy (blue color) and acupuncture treatment (green color) from ANOVA analysis across four groups. The red color indicates the mask of high pain minus low pain across four groups. L indicates left side of the brain, R indicates right side of the brain. rACC: rostral anterior cingulate cortex; MPFC: medial prefrontal cortex; LPC: paracentral lobule; PAG: periaqueduct grey; NL: lentiform nucleus; INS: insula; OPFC: orbital prefrontal cortex; NA: amygdala.

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