Prolonged Repeated Acupuncture Stimulation Induces Habituation Effects in Pain-Related Brain Areas: An fMRI Study

Abstract

Most previous studies of brain responses to acupuncture were designed to investigate the acupuncture instant effect while the cumulative effect that should be more important in clinical practice has seldom been discussed. In this study, the neural basis of the acupuncture cumulative effect was analyzed. For this experiment, forty healthy volunteers were recruited, in which more than 40 minutes of repeated acupuncture stimulation was implemented at acupoint Zhusanli (ST36). Three runs of acupuncture fMRI datasets were acquired, with each run consisting of two blocks of acupuncture stimulation. Besides general linear model (GLM) analysis, the cumulative effects of acupuncture were analyzed with analysis of covariance (ANCOVA) to find the association between the brain response and the cumulative duration of acupuncture stimulation in each stimulation block. The experimental results showed that the brain response in the initial stage was the strongest although the brain response to acupuncture was time-variant. In particular, the brain areas that were activated in the first block and the brain areas that demonstrated cumulative effects in the course of repeated acupuncture stimulation overlapped in the pain-related areas, including the bilateral middle cingulate cortex, the bilateral paracentral lobule, the SII, and the right thalamus. Furthermore, the cumulative effects demonstrated bimodal characteristics, i.e. the brain response was positive at the beginning, and became negative at the end. It was suggested that the cumulative effect of repeated acupuncture stimulation was consistent with the characteristic of habituation effects. This finding may explain the neurophysiologic mechanism underlying acupuncture analgesia.

A New Method for Sham‐Controlled Acupuncture in Experimental Visceral Pain – a Randomized, Single‐Blinded Study

“…This technique has been used to investigate correlations between acupuncture and brain activity. Interestingly, an increase in sensorimotor cortical activity along with decreases in limbic–paralimbic–neocortical activities was found in several studies . Hence, the observations suggest that not only sensory processing, but also emotional, and cognitive functions play an important role for acupuncture responses.…”

Activation of hippocampal MEK1 contributes to the cumulative antinociceptive effect of electroacupuncture in neuropathic pain rats

“…This may explain why in the first four sessions of EA intervention, MEK1 activation in rats with EA was higher than that in CCI animals. A study showed that the cumulative effects in the process of repeated acupuncture stimulation may be an interesting characteristic of bimodal habituation [9]. In other words, information induced by repeated EA stimulation may form a type of habitual memory in the hippocampus.…”

“…Several lines of evidence demonstrated that the short-term effect of a single session of acupuncture stimulation differs from the cumulative effect of multiple sessions of acupuncture stimulation, which may depend on the differential modulation of immunologic factors and neurotrophic signaling molecules [7–9]. Our previous study showed that the cumulative analgesic effect of repeated electroacupuncture (EA) intervention in neuropathic pain rats is closely associated with its regulatory effects on natural killer cells as well as some splenic and plasma cytokines [10].…”

Acupuncture: Emerging evidence for its use as an analgesic (Review)

“…Acupuncture has numerous functions (1-3), including use as an auxiliary method of treatment for acute or chronic pain (4,5). Certain studies have proposed that acupuncture-induced analgesia is a complex physiological adjustment process that involves the entire nervous system, including the central nervous system (CNS) and the peripheral nervous system (6)(7)(8). Mechanisms underlying acupuncture are intimately associated with neurohumoral and neurotransmitter pathways.…”

“…Mechanisms underlying acupuncture are intimately associated with neurohumoral and neurotransmitter pathways. A number of studies have hypothesized that acupuncture may play a role in inducing analgesia (8)(9)(10)(11)). …”