TENS and the remarkable power of suggestion

In clinical trials of a new drug it's easy to implement a placebo (comparison) group. Just give people a pill that looks the same as the active pill yet is absent the active ingredient. Many participants will try to determine to which group they had been assigned, but it will usually be difficult to do. Now some individuals will try to figure it out by whether they have any side effects (patients will have been told of potential side effects as part of the risks of participation during informed consent), but this is not a reliable because some people who are in fact in the placebo group (and receive nothing but starch) will exhibit side effects, perhaps because they are anticipating them (this is known as the placebo effect's dark side counterpart: nocebo effects). But in the case of non-drug treatments it can often be very tricky to develop a useful comparison group.

For example, say you want to investigate the efficacy of transcutaneous electrical nerve stimulation (TENS). TENS involves the delivery of electrical currents through the skin to the nerves. When a TENS unit is operating you feel it as a tingling sensation. People know this and they will get suspicious if that tingle is not there! So you can compare a treatment session with real TENS against a "sham" treatment in which all the equipment is there and used as it would be used during a real TENS session except that the electricity is turned off. But this is not likely to fool people and this will tend to lead to overestimates of TENS efficacy because suspicious people will have lowered their expectation for improvement, thereby widening the gap between improvement due to the specific action of TENS and improvement due to placebo effects.

Well I came across a study (Langley, Sheppard, Johnson, & Wigley, 1984) that was actually done many years ago but the findings were very intriguing I thought. They randomly assigned rheumatoid arthritis (RA) outpatients to one of 3 groups: Groups A and B received two different forms of electrical stimulation and Group C (the placebo group) received no electrical stimuli but instead watched a representation of TENS electrical stimulation on an oscilloscope. The researchers found no difference between on any of the groups on changes in resting pain and grip pain from pre- to post-treatment in these RA patients. This means that even in the absence of any tingle sensation they accepted the visual feedback as sufficient evidence that they were receiving TENS treatment, which was enough to boost placebo effects to those achieved by the TENS treatment, with the tingle and all.

The power of suggestion really is almost magical. We want to believe. We really do. Especially people who are in pain (as these RA patients were) and are looking desperately for relief. We will latch onto the evidence is support of our beliefs while ignoring even strong evidence to the contrary.

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Langley, G. B., Sheppeard, H., Johnson, M., & Wigley, R. D. (1984). The analgesic effects of transcutaneous electrical nerve stimulation and placebo in chronic pain patients. A double-blind non-crossover comparison Rheumatology international, 4(3), 119–123.