Double-blind acupuncture needle: a potential tool to investigate the nature of pain and pleasure

Abstract

Background: Most of our knowledge about similarities in the neural processing of painful and pleasant sensations in the brain derives from studying each phenomenon separately. Patients often feel pain induced by acupuncture, which is noxious stimulation having the symbolic message of the cure, as pleasant.

Objectives: We investigated whether the double-blind acupuncture needles are potential tool to investigate coinciding pain and pleasant events.

Methods: Participants were 109 healthy acupuncture students. An acupuncturist applied the double-blind placebo and the matching penetrating needle at bilateral forearm of each subject, one needle on each side of the arm. We asked the subjects to rate the pain associated with needle application and its unpleasantness or pleasantness on a visual analogue scale.

Results: Of 65 penetrating needle applications that elicited pain, 29 (45%) subjects did not describe the pain as being unpleasant, and interestingly, 18 (28%) subjects described the needle insertion as pleasant. There was no significant difference in reported pain intensity between penetrating needles elicited pain that elicited a pleasant sensation and those that elicited an unpleasant sensation (P = 0.34).

Conclusions: The double-blind acupuncture needles can be a potential tool for investigating the concomitant hedonic (pleasure) experience of pain.

Keywords: Acupuncture; Double-blind; Hedonic; Pain; Pleasure; Reward.

Figure 1

The design of the double-blind (practitioner-patient blinding) skin-touch placebo needle and matching penetrating needle [3, 4]. Both needles comprise an opaque guide tube (1) and upper stuffing (2). The body of the penetrating needle (3) is longer than the guide tube by an amount equal to the insertion depth, but the needle body of the skin-touch placebo needle (4) is just long enough to allow its blunt tip to press against the skin when the needle body is advanced as far as possible. The skin-touch placebo needle contains lower stuffing (5). Both needles have a stopper (6), which prevents the needle handle (7) from advancing further when the sharp tip of the penetrating needle (8) or the blunt tip of the skin-touch placebo needle (9) reaches the specified position. The pedestal (10) on each needle is adhesive, allowing it to stick firmly to the skin surface.

Figure 2

Pain intensity for the penetrating needles with a pleasant sensation and with an unpleasant sensation. There was no significant difference between the penetrating needles with the pleasant sensation and those with the unpleasant sensation in the subjects who had pain associated with needle insertion. Pain intensity was expressed on 100 mm visual analogue scale. The top, middle, and bottom lines of the boxes correspond to the 75th, 50th, and 25th percentiles, respectively. The whiskers extend from 10th to the 90th percentile. The circles indicate the arithmetic mean.