Friday, 15 November 2013

Placebo and nocebo: conscious thought not required

I went to a fascinating New Scientist Live event earlier this week. They're launching a new book literally about Nothing -- from the number zero to the state of mental nothingness induced by anaesthetic. Helen Pilcher was there talking about the nocebo effect, the "evil twin" of the placebo effect. Most of you are undoubtedly familiar with the placebo effect. This effect, also known as homeopathy (in my humble opinion), is when sick people actually do get better by taking pills containing no medicinal ingredients. It's a fascinating effect and seems to happen to about 1/5 of people in any given trial. For years I thought of the placebo effect as a 'mind over matter' type thing, where positive feelings cause the release of neurotransmitters that subsequently make the person actually feel better. My favourite fact about the placebo effect, though, is that even people who know the pills they're taking contain nothing but sugar still feel better when taking them. Mind over matter has nothing to do with it. Disappointing, really-- I've always had a soft spot for the idea of a positive attitude enabling us to overcome anything. Science once again fails to bend to my will.

The nocebo effect is the placebo effect inverted. People experiencing the nocebo effect have deteriorating health because they're told they're going to get sick. Helen spoke about witch doctors placing curses, about patients in clinical trials overdosing on sugar pills, and about the reluctance of surgeons to operate on people who think they're going to die during surgery. An unusually large number of those who think they're going to die during surgery indeed do, ruining our poor surgeon's statistics. So is the nocebo effect, unlike the placebo effect, actually a 'mind over matter' phenomenon?

Some fascinating work from researchers in Boston suggests that consciousness isn't required for the nocebo effect either. Fist, volunteers were conditioned to associate high and low pain with two different faces. When patients were shown face 1, they were simultaneously given a painful heat stimulus. When they were shown face 2, they were simultaneously given a mild heat stimulus. Then they were shown those same faces while an intermediate level of heat was applied, and as you'd expect, the volunteers reported feeling more pain while they were looking at face 1. Now comes the interesting part. The experimenters then showed the faces so quickly that the volunteers were unable to consciously recognise them. Again, face 1 elicited more pain than face 2, despite identical heat stimuli.

So much for the conscious mind over matter there, too. There's something much more primal going on to cause these two effects. Perhaps patients who are genuinely at an increased risk of dying during surgery can somehow feel that something is just a bit off. I don't think, as Helen does, that these patients die not from the disease, but from believing that the disease will kill them. There's something else going on here. Belief has nothing to do with it.