Dorsolateral prefrontal cortex sensing analgesia

Abstract

Chronic pain often has an unknown cause, and many patients with chronic pain learn to accept that their pain is incurable and pharmacologic treatments are only temporarily effective. Complementary and integrative health approaches for pain are thus in high demand. One such approach is soft touch, e.g., adhesion of pyramidal thorn patches in a pain region. The effects of patch adhesion on pain relief have been confirmed in patients with various types of pain. A recent study using near-infrared spectroscopy revealed that the dorsolateral prefrontal cortex (DLPFC), especially the left side, is likely to be inactivated in patients experiencing pain relief during patch treatment. Mindfulness meditation is another well-known complementary and integrative approach for achieving pain relief. The relation between pain relief due to mindfulness meditation and changes in brain regions, including the DLPFC, has long been examined. In the present review article, we survey the literature describing the effects of the above-mentioned complementary and integrative treatments on pain relief, and outline the important brain regions, including the DLPFC, that are involved in analgesia. We hope that the present article will provide clues to researchers who hope to advance neurosensory treatments for pain relief without medication.

Keywords: chronic pain; complementary and integrative treatment; mindfulness; near-infrared spectroscopy; pyramidal thorn patch.

Figure 1

Pyramidal thorn patch. (A) The pyramidal thorn patch has a diameter of 3 cm and a thickness of 0.1 mm, and the tapered pyramidal thorn constructed from low-density polyethylene is 3 mm high and 7-mm square. (B) Application of pyramidal thorn patches to a pain region (e.g., lower back). After palpating to determine the pain region, several pyramidal thorn patches were applied to alleviate the pain. Reprinted from [21] under a CC BY license.

Figure 2

The dorsolateral prefrontal cortex (DLPFC). (A) Schematic representation of the left DLPFC as indicated by the dashed circle. (B) Changes in oxyhemoglobin levels normalized with the Z-score before (Pre) and after (Post) patch treatment in patients with pain. In the left DLPFC, oxyhemoglobin levels tended to be reduced during patch treatment (Wilcoxon signed-rank test, P=0.058). This reduction was supported by the correlation coefficient (r=0.68) calculated for the left DLPFC activity between before patch treatment (i.e., Pre) and after patch treatment (i.e., Post). Reprinted from [21] under a CC BY license.