A recent study  found In the pain+TENS condition, PAG functional connectivity with the lateral prefrontal cortex increased, likely activating the descending pain-inhibitory pathway. As well, the superior parietal lobe, right postcentral cortex (S1), bilateral parietal operculum (S2), supramarginal cortex, and right ventrolateral prefrontal cortex (VLPFC) were all significantly activated in the pain+TENS condition when compared to the pain-only condition. This may indicate the stimulation of large-diameter A-beta fibers, leading to reduced pain.

In the pain-only condition, the left anteroventral thalamus, bilateral rACC (rostral anterior cingulate cortex), and right hippocampal cortex were more highly activated. The anterior thalamic nuclei have many projections to the ACC, which has been shown to process the affective-motivational dimension of pain. The hippocampal cortex activates in response to noxious stimulation and may contribute to negative effect associated with pain. Left PAG functional connectivity with the left, but not the right, lateral prefrontal cortex (PFC) significantly increased as the TENS effect increased in the pain+TENS condition. Both the lateral PFC and PAG are implicated in endogenous pain inhibition. Thus, the increase in TENS effect may activate the descending pain-inhibitory pathway.

The participants reported lower perceived pain and pain-related unpleasantness in the pain+TENS condition compared to the pain-only condition.

STUDY TITLE: Brain mechanisms of pain relief by transcutaneous electrical nerve stimulation: A functional magnetic resonance imaging study
Authors: Choi JC, Kim J, Kang E, et al.
Publication Information: European Journal of Pain 2016; 20: 92–105.

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