The “Health Governor”Published 17 September, 2012
A new little piece in Current Biology by Nicholas Humphrey and John Skolyes entitled “The evolutionary psychology of healing: A human success story,” is one paper in a Special Review issue on Evolution and Human Health. The article poses the following question about the placebo effect:
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? (p. R697)
I’m fond of their answer, which can be summarized in a word that figures prominently in my own lexicon: tradeoffs. They explain the idea with what they call the “health governor,” a term used as something of an homage to Hill’s notion of a “central governor,” a proposed system that works to inhibit physical activity to reduce the chance of damage by continued exertion. Here’s the figure from the paper illustrating the idea.
In the model, deployment of resources to heal are expensive, and so must be deployed based on a cost/benefit calculation. Increasing the activity of some element of the system – the immune response, for instance – carries the potential benefit of fighting off parasites, but comes at substantial metabolic costs, which must either be replaced or diverted from other uses. Just like a (political) Governor, there are budget tradeoffs that have to be made (e.g., fighting the war on drugs comes at the expense of allocations to education or health care for children.)
On the left side of the figure are inputs to the putative governor system, cues associated with threats to health as well as cues associated with current and future resources that can be deployed. In the center is the proposed computational system, weighing the threat posed, taking into account, presumably, the opportunity costs of using resources for healing. On the right are the outputs of the system, including features that carry greater or lesser costs. (In the middle is a captain rather than a governor, which seems to put the metaphor out at sea, but the point is clear.)
Note “Social support” toward the bottom of the list of inputs on the left side. The idea here is that cues that one has social support can influence the cost/benefit calculus of deploying healing resources. If I have others to help me replace additional resources that I might expend for healing, then I might increase the healing budget to a level higher than I otherwise would. Placebo effects, on this view, are various kinds of inputs to the governor system, moving around the best tradeoff between deploying healing resources and husbanding resources for other uses.
While the article itself is short, the authors work in some interesting findings. One such study that caught my attention is some work on Siberian hamsters. (These critters seem to show up in research with some frequency.) In the study, researchers injected hamsters with pathogens, with different hamsters having different “beliefs” about what season it was through the use of artificial lighting. Hamsters who thought that Winter Is Coming (in fine Stark fashion) husbanded resources while those who thought summer was nigh showed greater immune responses. In humans, Humphrey and Skolyes report work showing that an injection the patient can’t see reduces pain only half as much as an injection the patient can see.
So, the answer to the question I began with is that just because healing is possible doesn’t mean that it’s a good idea, given the price tag of healing. Optimal healing, as it were, depends on the costs and benefits of the different options. Further, as illustrated in the figure, these costs and benefits might depend on many factors, including the nature of the threat, reserves, the social world, guesses about the future, and so on. Optimal healing is likely to be, in a word, complicated.
It might seem slightly odd to have pain as an output on the right side, particularly because it doesn’t seem like (the phenomenology) of pain is costly. But there are costs in the form of all of the activities that the pain discourages or makes impossible. In that sense, pain can be thought of as carrying opportunity costs, whatever the benefits would be of the actions that could be taken without the experience of pain.
Readers of this blog might be interested in other articles in the Special Issue, and I’ll be saying more about tradeoffs, phenomenology, and opportunity costs soon.