Monday, August 25, 2014

Pain and Your Brain

Everyone is familiar with placebo effects.  Just taking a pill can reduce pain you are feeling, even if that pill has no active ingredients in it.  Indeed, placebo effects help even when you are taking an active ingredient.  I know that when I have a headache, taking some ibuprofen starts helping the pain fairly quickly, even though it can take up to 30 minutes for the medication to have an effect. 

It is hard to study pain and placebo effects, because pain is subjective.  That is, you can’t know whether people are experiencing pain unless you ask them.  If people want sympathy, they might exaggerate their report of pain.  If they want to avoid worrying their friends and relatives, they might minimize their report of pain. 

In addition, there may be many different psychological systems involved in pain, and different treatments might influence these systems in different ways.  But, people are only aware of the experience of pain.  So, just focusing on the pain people are feeling does not help researchers to tease apart the various ways that pain might be reduced.

An interesting paper by Tor Wager and Lauren Atlas in the January, 2013 issue of Perspectives on Psychological Science reviews evidence from brain imaging to tease apart the influences of placebos on pain.

In order to study placebo effects, it is important to know the regions of the brain that are involved in the sensation of pain.  Wager and Atlas first review studies in which participants were exposed to low-intensity and high-intensity heat in a functional Magnetic Resonance Imaging (fMRI) study.  The fMRI technique measures blood flow in the brain and gives researchers information about areas of the brain that are active in different situations. 

If you are interested in the specific brain areas associated with pain, check out original paper.   For now, what is important is that these brain areas provide a way for researchers to explore different effects of placebos. 

Researchers have suggested that placebo effects might reduce pain by activating opioid receptors in the brain.  Opioid receptors are the ones that opiate drugs (like morphine and codeine) activate.  The brain has natural chemicals that activate these receptors, and that helps minimize the experience of pain.  For example, research has shown that placebo effects are reduced by giving a person a chemical that blocks the activity of the opioid receptors.

One observation from these fMRI studies is that a region of the midbrain (see the figure for a sense of where the midbrain is located) is influenced by opioid receptors.  This area of the brain is affected by placebos.  In addition, areas of the frontal cortex of the brain (located in the brain above your eyes) is also related the strength of placebo effects. 

Here is where it gets interesting.  There are other areas of the frontal cortex that are involved in your ability to control your thinking.  Those areas of the brain are not involved in placebo effects. However, researchers also know that if you distract yourself, that can minimize the experience of pain.  Presumably, distraction involves these brain areas that are associated with thought control.

Based on these observations, other studies using brain imaging show that distraction does reduce pain, but it uses different brain regions than the areas involved in placebo effects.  As a result, these two techniques can be added together for a more powerful effect.  That is, a combination of a placebo and distraction is better than either one alone.

Finally, the pain-reducing opiate drugs involve some of the same brain mechanisms of placebo effects and distraction, but they involve some different ones as well.  Which means that in cases of the worst pain, a combination of all three effects can be more powerful than any one alone.

You might wonder how you get a placebo effect when you have taken a real drug.  Remember, though, that just the knowledge that you have been given a drug engages some pain relief.  That happens regardless of whether that drug is a real painkiller or something inert.  So, telling someone they are getting a pain drug and then giving them that pain drug creates both a placebo effect and the relief from the drug itself.

This work is interesting in two ways.  First, it provides some new insight into how placebo effects work.  Second, it shows how the maturing science of brain imaging can help science tease apart complex mechanisms that would be hard to study without insight into what the brain is doing.