A new study performed at the University College London reveals that people are more suggestible under the effect of nitrous oxide – laughing gas. The study involved subject receiving nitrous oxide, and controls receiving regular air (both scented to disguise which was which) and then were asked to imaging an image or sensation and report on how vivid they believed it to be. Those getting nitrous oxide reported 10% higher on the scale of vividness, suggesting that they slightly more suggestible.

This effect is plausible, and also nothing new. Various compounds have been believed for a long time enhance suggestibility. Anything that inhibits our critical faculties would likely have this effect.

The study authors are particularly interested in how this effect of nitrous oxide can be exploited to enhance pain relief from anesthesia. They site that hypnosis has already been demonstrated to have such an effect, and perhaps the combination of nitrous oxide and hypnosis would have an additive effect.

Hypnosis, actually, remains somewhat controversial. But the most plausible claims made for it is that it helps some people relax, and this relaxation has been shown to reduce the subjective experience of pain during procedures. Whether or not there is a specific physiological effect, or if this is simply a psychological effect, is still a matter of investigation.

It does make sense that pain would be something that can respond significantly to suggestion – even without some enhancement. My personal experience bears this out. As part of my specialty I perform a procedure known as an EMG – it is a diagnostic study that involved small shocks of electricity to look at nerve function, or sticks with thin needles to examine the electrical activity of muscles. It’s an unpleasant test. Although this is anecdotal, it is my experience that patients tolerate the procedure better with a calming a reassuring bedside manner. Also, the EMG machine can make an audible “click” with every shock (I’m not sure what the purpose of this is, probably just as feedback for the operator). Patient’s tend to respond more to the shock with the click on than off. Even when the stimulus is identical, the presence or absence of the sound seems to have an effect.

There is also hard evidence that the experience of pain is easily manipulated by psychological factors. A recent study, for example, showed that subjects report higher levels of pain if they believed the person administering the pain meant them harm.

That the experience of pain if susceptible to numerous modifying psychological factors makes some sense. The purpose of pain is to alert us to an injury or threat. The context of the pain, such as our emotions at the time, whether or not it is accompanied by other stimuli, and whether it represents an ongoing threat, should therefore influence how much of our attention the pain provokes.

Further, in order to understand pain it must be known that there are two main components of pain from a neurological point of view. There is the sensation itself, which we recognize as a painful sensation, and completely separate from that is the negative emotional reaction to the pain. Narcotics operate more to relieve the emotional component of the pain than the physical sensation itself (although they do decrease both), and this can lead in some patients with severe pain to a situation in which the narcotic relieve the negative emotions of pain but not the sensation itself. Therefore, patients may still feel the pain, but it just doesn’t bother them. On the flip side, addicts who are withdrawing from narcotics can have an exagerated emotional response to even mild pain.

Clearly, when it comes to pain it is this emotional component that matters most. And this negative emotional response to pain can be manipulated by pharmacology, by mood, by the perception of threat, and (it seems) by suggestion.

It is therefore no surprise that pain generally has the most consistent and significant placebo effect in controlled trials – usually around 30% of subjects report a significant decrease in pain to a inactive treatment. This is critical to understand while investigating biological interventions aimed at pain – without controlling for this significant placebo effect it is not possible to draw conclusions about the biological activity of the intervention.

But also – this provides an opportunity to treat pain by exploiting its nature. That is what the authors of this study hope to do – find ways to use enhanced suggestibility to reduce the experience of pain during procedures, and perhaps reduce the overall need for pain medication.

Of course, this should be done responsibly – without lying to patients or invoking some form of “magic” to explain the effect.