How do we make sense of the placebo effect from an evolutionary perspective? In a recent paper in Current Biology, Nicholas Humphrey and John Skoyles noted an apparent paradox:
When people recover from illness under the influence of fake treatments, they must of course in reality be healing themselves. But if and when people have the capacity to heal themselves by their own efforts, why do they not simply get on with it? Why ever should they wait for third-party permission — from the shaman or the sugar pill — to heal themselves? How strange that people should be condemned to remain dysfunctionally sick just because — as must still often happen — they have not received permission.
Good questions! Here is how the authors try to answer them.
Many self healing mechanisms (such as an immune response to fight an infection) carry costs as well as benefits. For example, a fever can help kill a pathogen but is metabolically expensive. It is reasonable to assume that humans have some system that tries to determine whether a particular form of self healing is worth the cost. The authors call this system the "Health Governor." (If you think that sounds silly, its Latin version is far more impressive - the gubernator medicatrix.) A placebo treatment is simply a way to fool the governor into changing its mind about the relative costs and benefits of a particular self healing response.
The economics of health
Although we would probably all like to have greater amounts of strength, flexibility, and endurance, these qualities all come with costs which must be weighed against their benefits in any particular situation. For example, we need some strength to accomplish the functional tasks of life, but too much can result in forces that cause injury to the body.
According to Humphrey and Skoyles, the same is also true in regard to many aspects of the immune response.
The benefits of deploying such defenses are plain: the patient survives the illness. But the costs are plain too. Mounting an immune response is energetically expensive and uses up rare nutrients that will later have to be replaced. Starving bacteria of iron produces debilitating anaemia. Vomiting and diarrhoea waste fluid and food stuffs. Running a high temperature to kill fungi or bacteria raises metabolism by up to 50%. Pain, nausea, fatigue, and other ‘protective states of mind’ not only get in the way of performing essential tasks but are highly disagreeable…
Accordingly, there will often be times when deploying a particular defense will not be advisable. For example, it is probably better not to mount an energetically expensive full-blown immune response to an infection when there is a shortage of food. Pain can help to protect an injured ankle, but is probably more costly than beneficial when trying to outrun a predator.
Based on these facts, the authors conclude that there would have been selective pressure on human ancestors to develop a way to anticipate the costs and benefits of various self healing mechanisms, and then make intelligent judgment calls about whether to deploy them. The authors propose that such a system could be called a health governor, and created a chart to outline the factors it might consider in making decisions.
As you can see from the chart, the governor would likely consider various factors such as energy reserves, medical assistance, and social support in deciding whether to engage in certain protective responses, such as fighting an infection or creating pain.
The authors present a few quick examples of how the heath governor might work. Imagine you have some form of infection. The health governor might be more willing to pay the energetic cost of a high fever if it knows that food is readily available to pay back the debt.
The authors cite to research showing that hamsters will mount a far more vigorous response to an injected pathogen if it is tricked into thinking it is summer. When they think it is winter, their immune system will instead settle for a more prolonged battle with the virus called a “holding operation.” Ever notice that your cold lasts longer in the winter? We tend to think that our immune systems need a “boost” to finally conquer an invader, but according to Humphrey and Skoyles, sometimes all it really needs is the green light from the governor to fight harder. And maybe that sugar pill from the homeopath or hit of echinacea is all it takes to convince the governor that it’s go time.
Pain and action signals
So how would the health governor work in the context of pain?
David Butler and Lorimer Moseley start their explanation of pain by noting that pain is an action signal. Its purpose is to motivate you to take action to protect the body from perceived threats to the physical tissues. Once appropriate action is taken, the pain serves no further purpose. The items on the left of the health governor chart look quite a bit like many of the actions that Moseley and Butler suggest might be sufficient to end the need for many kinds of pain. Ever notice that your pain went away on the same day you went to the doctor? Or restored energy reserves by getting a good nights sleep? Or fooled your brain into thinking it's summer by going someplace sunny? Or got some social support by talking with an empathetic or a caring friend?
The importance of good news
The reason I like this paper is that it is yet another reminder that it is always a good idea to give the brain good news about the state of the body. Most of the things that bother us about our bodies or movements - stiffness, pain, poor coordination, fatigue, weakness - are simply the result of the brain trying to protect us from perceived threats.
The brain usually errs on the side of seeing threats and protecting us from them because it cares more about our survival than our comfort. So we can make ourselves more comfortable by giving the brain good news about the state of the body.
And I think that most therapeutic approaches to the body, such as manual therapy or corrective exercise, work primarily on this basis. Massage therapists, personal trainers, and physical therapists are all in the business of giving their clients good news:
- "Hey look, good news, you can actually move this joint into full flexion without pain."
- "Good news, you can squat all the way down to the floor."
- "Good news, you just did your first headstand in thirty years."
- "Good news, you just deadlifted twice your bodyweight, that is pretty bad ass."
- "Good news, you can run five miles and not die."
And we don't need to pay therapists to get the really good news, which really supports good health, like that we have loving family and friends, that the sun is shining, and that we have meaningful and rewarding jobs. If these things are true for you, to whatever extent, make sure your brain is very aware of them. That's a healthy thing to do.
Have you given your health governor any good news today?