Pain relief associated with decreased oxyhemoglobin level in left dorsolateral prefrontal cortex

Abstract

Pain in the elbow, shoulder, knee, lower back, and various other joints is relieved by adhesion of pyramidal thorn patches. To elucidate the pain relief mechanism induced by the patches, we established a quantitative method for estimating the pain reduction and investigated the brain regions that change in association with pain relief. We first attempted to quantify the pain relief using transcutaneous electric stimulation (TCES) and a visual analog scale (VAS), and then applied near-infrared spectroscopy (NIRS) to the prefrontal cortex, including the dorsolateral prefrontal cortex (DLPFC) and the orbitofrontal cortex (OFC). We also examined the salivary oxytocin levels, which are thought to reflect oxytocin secretion levels from the posterior pituitary in the brain. Application of pyramidal thorn patches to pain regions decreased the pain degree estimated using TCES and VAS. Oxyhemoglobin levels were likely to be decreased in the left DLPFC on the basis of NIRS measurements during patch treatment, suggesting that the left DLPFC is involved in pain relief. On the other hand, the salivary oxytocin levels varied widely. A potential reason for the varying salivary oxytocin levels is its utilization in the pain region as an analgesic agent. Our results suggest that the left DLPFC will become a target brain region for pain therapy.

Dorsolateral prefrontal cortex sensing analgesia

“…Previous studies by Miyashiro and colleagues showed that application of pyramidal thorn patches to pain regions decreased the degree of pain, leading to a lower oxyhemoglobin level in the left DLPFC [ 21 ]. That is, the left DLPFC is involved in pain relief.…”

“…The values measured in TCES indicate the ‘pain degree’, which can be calculated from the current perception threshold, defined as the lowest electrical current detected by participants, and the pain-compatible electrical current, defined by the electrical current judged by each experimental participant to be compatible with the intensity of the ongoing pain. The usefulness of TCES for pain relief has also been confirmed [ 21 ].…”

“…Application of the pyramidal thorn patches to various pain regions in 300 patients relieved the pain in almost all the patients within 4 treatments [ 18 ]. The decrease in pain induced by patch adhesion was observed by both VAS and TCES [ 18 , 21 ]. The patches were repeatedly applied until the participant states that the pain disappeared.…”

“…Using NIRS, Miyashiro et al investigated the brain regions, especially the DLPFC, associated with pain during patch treatment [ 21 ]. NIRS is considered suitable for studies of pain-induced changes in brain [ 28 ].…”

“…Previous studies, including Miyashiro’s studies [ 21 ], suggested that the DLPFC, especially the left side, plays a key role in pain relief. A contrary suggestion has been proposed as follows: the left DLPFC might be ‘activated’ before patch treatment because the patients ‘expect’ the pain relief.…”