Leaving the Land of Woo

Tags: placebo effect

We hear a great deal about the placebo effect, especially in discussions of alternative medicine.  Critics of alternative medicine point to the placebo effect as explaining the reported success of treatments that have no rational basis.  Despite there being no evidence that the alternative techniques are having any real effect, customers report that they feel better.  So what is the placebo effect, and how does it work?

Let's first describe some of the characteristics of this effect.  It was found out, back in the 50s, that if patients were told they were receiving real treatment when they were actually receiving fake treatment, they still reported feeling better.  In other words, simply the belief alone that they were receiving treatment, influenced patients to report an improvement in how they felt.

For many years it was believed that this represented a real clinical effect, that they were in fact getting better.  But in 2001, there was a systematic review of clinical trials and this showed that although the patients claimed to feel better, in fact they weren't. The placebo effect is restricted to the reporting of how patients feel, and does not describe their actual clinical condition and this view is supported by the Cochrane Collaboration review as well.  So we are dealing with a subjective effect.

Anticipation and expectation
To understand the placebo effect, we need to understand a little about how the brain works. In order for us to move around in the world, we have to have a picture of how the world is, how it behaves, the physical properties of objects, and so on.  We get information about all this from our senses.  Our brain collates that information and constructs a model of how the world is.  Normally it works fairly well and the brain continually corrects its model whenever something seems not quite right.  We might have thought that snakes were wet but on touching them, we discover they're dry.  The model was incorrect, and on getting new sensations, it's updated.  Our model of the physical world is continually updated giving us more and more predictability.

When we are moving around in the world, our brains continually make predictions about what we can expect.  We expect ice to be cold and so we anticipate the feeling of cold before we touch it.  That anticipation affects our body, for example our muscles tense, and we are already primed for the sensation.

This pattern of expectation and anticipation affects the state of our body.  When we catch a ball, we have already made a prediction about the speed and weight of the ball and adjusted ourselves accordingly.  If what we are expecting doesn't actually happen, that signals to the brain that the model is wrong in some respect - and the brain corrects it.  But the important point is that the priming, that readiness, has already taken place.

The brain mimics the sensation it is expecting to receive and produces a reaction in the body in anticipation.  This can be seen in brain scans.  When a person is expecting to grasp something, the areas of the brain associated with grasping objects shows increased activity before anything physical has happened.  The brain anticipates, creates an effect, then compares it with the real effect.  If they're different, the model is corrected.

We have a very simply example of this when we empathise with someone, when we feel what they are feeling.  Someone is feeling sad and we subtly adjust our own facial expression to mimic theirs, in a small degree.  The set of changes in our facial muscles stimulates just those areas in the brain which are more active when a person feels sad.  That enables us to experience similar feelings and therefore to show empathy. The brain affects the state of our body, and the state of our body affects our brain. It's a feedback loop which continues to adjust and correct the brain's model of the world.

The placebo effect is exactly the same thing happening in our brains, but brought about by the expectation of receiving some treatment.  When a person goes to receive treatment, they are already primed with the expectation that the treatment will do them some good.  They are expecting to feel better as a result of the treatment and therefore their brain primes them to feel better even before any treatment is received.

This effect can be shown with brain scans using fMRI (functional magnetic resonance imaging) which shows the increase in brain activity in different regions of the brain in real time.  Just the anticipation of receiving treatment for pain affects those precise areas of the brain associated with pain reduction.  Increased activity in this area of the brain is also associated with the release of analgesic hormones, some of them opioids.

The placebo effect is part of the anticipate-predict-and-test cycle by which the brain adjusts its models of the world.  The very act of anticipation, causes the brain chemistry to change in ways similar to, but less than, the actual event.  The brain uses the discrepancy between what was expected and what happened to update its model.

So antipating pain relief provides some relief, but it is not directly addressing the source of the pain.  Arguably it is obscuring it, making treatment more difficult.  For the patient of course, the placebo feels as though some relief has been given and they report feeling better, but the underlying condition has not been addressed.

In addition, in our society we are conditioned to have certain expectations of the medical profession and, in fact, in anyone who calls themselves a therapist and claims to be qualified.  We are conditioned to believe that they are able to provide cures, pain relief, treatment which will makes us feel better.  This conditioning reinforces the expectation, amplifying the placebo effect.

Placebo as treatment?
The placebo effect is nonetheless remarkably fickle.  It can be evoked by sympathy alone, by listening while a patient describes their problem, by unrelated actions that the patient is told are relevant, by ritual actions, and a host of others.  A placebo effect invoked on one occasion may fail completely the next time it is tried, or stop at any moment.  In other cases, the placebo effect can last for years.  Devoutly religious people can experience the placebo effect from prayers for many years, reinforced by regular participation. This is the reason that so many alternative therapies claim positive responses from customers, regardless of the range of irrelevant actions undertaken.  Acupunture is just as effective if the needles do not puncture the skin. The expectation and anticipation of the patient is sufficient to generate the placebo effect, and the effect of the ritual is not to deliver treatment, but to convince the patient they are receiving something.

But surely, if the placebo effect actually makes people feel better, it's a kind of treatment isn't it?

Unfortunately the answer is an emphatic no.  It is unfortunate because if it was possible to treat people using the placebo effect, it would save a great deal of money and have widespread application.  The problem is that it affects only the mental model and not the physical model, the patient's subjective state and not the body.  Patients may feel that their bodies have got better, but in fact they haven't. In cancer patients, that's a dangerous illusion.

Studies in 2001 and 2004 by Hróbjartsson and Peter Gøtzsche studied 156 clinical trials to compare whether the clinical outcomes of placebo were better than no treatment.  They weren't. Placebo is not treatment.

Interestingly there is a reverse effect also.  The nocebo effect is one in which patients report a worsening of their condition when given a treatment of which they disapprove.  Again, this is a subjective response and does not reflect the objective condition of their bodies.  Whether they thought they had worsened or not, did not affect the fact of their actual condition.