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Applications of Economic Models to Physiology?

by johnswentworth1 min read10th Dec 201922 comments

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Applying economic models to physiology seems really obvious. For instance:

  • Surely the body uses price signals to match production to consumption of various metabolites. Insulin as a price signal for glucose is one example.
  • Presumably such price signals coordinate between spatially-separated organs with specialized roles in various physiological "supply chains". That should lead to general equilibrium models, and questions of convexity and stability.
  • Can we back out an implied discount rate for the body's long-term energy stores?

Yet when I run a google search for the obvious phrase "econophysiology", I get back five results, most of which appear to be misspellings. (I feel like I ought to write something right now just to call dibs on the name.)

Does anyone know of sources on this sort of thing? Is there a name for it?


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22 comments, sorted by Highlighting new comments since Today at 2:18 PM

Not what you're looking for but it reminded me of how strange it is that people think of The Republic as a political treatise when the work bills itself multiple times as a work on psychology using political theory as extended metaphor.

In case people are confused by this: I believe the analogy is that people think of economics as a theory of human markets, even though the math is largely about general properties of distributed optimization.

Related: Fungus arbitrage https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6584331/

What is the difference between a generic "signal" and a "price signal"? What is a "price" in physiology? I think it would be interesting to see what insights an economic perspective of physiology would provide, but the constructs need to be defined pretty clearly so analogies can be drawn.

Another question is which basic assumptions embraced in economics can reasonably apply to the units of analysis in physiology (cells, etc.). Economists already have a hard enough time validating assumptions for humans.

What is the difference between a generic "signal" and a "price signal"? What is a "price" in physiology?

A price signal would need a few properties:

  • It would be paired with some physiological resource - it represents the price of something
  • It would be nonlocal, like e.g. a hormone - the point of prices is to coordinate in a distributed system
  • Local systems would increase/decrease their consumption of the resource in response to low/high price signal, and vice-versa for production
  • Some mechanism would make the price signal high when the resource is scarce, and vice versa, so that the amount of resource supplied matches up with the amount demanded.

Insulin is a good example: it acts as (inverse) price signal for glucose. It's a hormone, and many cell types throughout the body increase/decrease their glucose consumption in response to insulin level. The beta cells in the pancreas act as a market maker, setting insulin levels so that glucose supply matches demand over the long run.

Another question is which basic assumptions embraced in economics can reasonably apply to the units of analysis in physiology (cells, etc.). Economists already have a hard enough time validating assumptions for humans.

This is a point which I think is severely under-appreciated both in and out of economics: it is often far easier to apply economic models to systems in biology than to humans. Humans have complicated, opaque decision-making procedures. We can't observe those procedures directly, and have to make indirect predictions about their effects. Cells have decision-making procedures which we can directly observe and model, and people have already built many of those models.

Conversely, many of the debatable assumptions economics make about humans would have directly-observable effects in biological systems. If subsystems' behavior can't be described by utility functions, then that will directly result in resources consumed to produce things and then destroy them without using them. To the extent that such energy waste is minimized, the system behavior can be approximated by utilities. Another example: if subsystems' revealed preferences aren't concave, then that will directly result in instabilities in physiological behavior.

To really compare to an economic price signal, it should be a resource transfer from one actor to another - the price "paid" by a buyer is equal to the amount "received" by the buyer. I don't see this for most physiological processes - they are signals, but more like feedback loop and control theory signals than they are price signals. There _are_ symbiosis/parasite cases that are closer to a price system, where one organism gives up something to another, in exchange for future benefits.

That's not necessary for all results. It would be relevant to some - e.g. monetary economics (obviously), budgets constraints, and anything where the role of money as an incentive is crucial. But it's not needed for e.g. much of price theory, which is the main sort of application I imagine. Indeed, if we look at Glen Weyl's definition of price theory, it immediately sounds like it would be applicable to many problems in biology.

(Also, I suspect one could work around the absence of a budget constraint by directly observing the consumption function.)

I've also spent 30 minutes looking for anything in this space and didn't find anything. The closest that I could find was Neuroeconomics.

IIRC neuroeconomics is quite different: it studies how humans make and represent economic decisions (eg "we've found an fmri signal in the orbitofrontal cortex that's correlated with expected value of this decision"), which is different from modelling the internal physiologial functions of a body as an entire economy with various supply chains and equilibrium states.

I think neuroeconomics is behavorial economics for people with fMRI fetish. Even when the name points in the right direction it's not about application of economical models to neuroscience.

Like one of the comments below I am a bit skeptical. However, I would be curious to learn more about the motivation to apply this type of analysis for physiology.

See my response to leggi's comment, with the dog picture, as well as to Daniel V.

This is a bit tongue in cheek but " There's a dog in the picture. Once you see the dog, there's still a lot going on in the picture, but the whole thing makes a lot more sense. " suggests we should not be taking pictures of dalmatians with high contrast black and white films ;-)

At the same time I think that does get to the core of the discussion, for me at least. High contrast images are really good for certain things, no so much in other settings. So while economic concepts may shed some light on yet unanswered questions -- or perhaps merely suggest questions we have not yet thought about due to framing type blinders -- I think one needs to tread carefully.

I do agree with your, and ChristianKI's, position that some of the underlying economic concepts, theoretical at least, may actually be wheels we can put on another cart and make some progress. But from that perspective it's really just the abstract math model and not really economics. I do think using existing wheels is often a pretty good idea. But I also think periodically reinventing the existing wheels is also a pretty good idea too.

So here would be more specific questions I have about the general idea:

1) With pricing I'm not convinced by your answer that we really get anything more, even if the additional properties are really anything more than terminological differences from any other signally mechanism. Nor am I really seeing what more we're learning or can learn with the change to the economic price model here. What new insights are expected here -- or what can the current model approach not tell us but that seem to be rather important?

Some other observations. Insulin as a price is problematic to me on two counts. First, even taking it as such it seems to get us a partial equilibrium model at best so tells us very little about the overall state of the system. Second, it's not clear to me just what type of price it would be. It's not like a dollar price where we see the underlying monetary unit as common across all the local prices. Insulin is one of the many hormones in the human body and we don't seem to have a common unit that would underlie all the hormonal signaling mechanisms. If so then that price will be more along the line of a barter market "price".

I think a lot of people lose sight of what prices are and see them purely as a signalling device (the Hayakian information signals in society) but prices are both signalling devices and rationing devices. Is the idea to looks at the relative prices within a body and induce rationing on consumption of certain resources and the increased production of other resources?

2) Discount rates. I cannot really think of a good use here, even if we can (easily I suspect) calculate such a rate. The implication is see is that those with more fat should have a lower discount rate for future energy meaning they save more. But is that a really good description of the amount of fat more people have? I would think a better description might be trash we're unable to dispose of fast enough so it's just pilling up on the streets and empty fields. Still, you might be seeing a number of things I'm not.

3) When thinking about economic processes and physiological process how do things like , production possibility frontiers or scarcity compare? Is the body's normal state of operation one of scarcity or perhaps non-scarcity? Does it the body always operate on it's PPF? If we're not in a state of scarcity will the economic concepts (which I would to some extent separate from the underlying math) that all derive entirely from that starting point really apply?

I do think the ideas of always moving towards some equilibrium state, and generally never actually being at the point, applies to both settings. On that basis I might see where cross pollination might be good -- but I still don't quite see a benefit to adopting any of the terminology and resulting mental imagery will help and have certain fears it will mislead.


Those are all reasonable questions to ask and points to raise, and I'm not going to go to bat defending any of the suggestions I made off the top of my head when writing the original question. The point of the original question was to see if anybody out there had publications asking/answering the sort of questions you pose, and it looks like the answer is "no".

For some of these questions, as you argue, it's possible that the lack of literature is because there really isn't anything interesting to be found. But at least some of these questions would be interesting to have an answer to regardless of what the answer is - e.g. your example "Is the body's normal state of operation one of scarcity or non-scarcity?".

More generally, a better analogy than the dog picture would be the periodic table. At first glance (and certainly before the development of quantum theory) an argument could be made that it doesn't tell us anything we can't figure out without it. But it did hint at what questions to ask - e.g. undiscovered elements and their properties. If insulin acts as a price signal (even without a rationing role) or if the body's fat stores are governed by an internally-represented discount rate, then that immediately suggests that a variety of different cell types would look at those signals to determine their behavior - possibly cell types and behaviors not yet examined. It also predicts that cells which convert one resource into another would examine the corresponding price signals, and adjust production based on relative prices. Like the periodic table, these ideas suggest relationships to look for.

Thanks, and I seem to have come across as more critical/confrontational than I actually felt (so seemed to have been demanding some defense from you - sorry). My intent was to better tease out what type of questions you might be asking and hoping to answer. I understand your thinking and motivation bit better now.

No problem, and they are great questions. :)

In economics people have proven a lot of math about how certain processes behave. If you could reuse the theorems that are already proven outside of biology in the biological context, that would be helpful.

Trying to explain biology with economic terms is an interesting proposal (creating a story that you can understand?) but it would not be the obvious thought to me.

economic models = made up by humans

physiology = millennia of chance and adaptions under various pressures, creating immensely complex systems that just blow my mind.

The insulin analogy is flawed in many aspects.

There is a basic feedback loop of increased blood Glucose --> increased insulin --> lower Glucose --> reduced insulin to keep blood glucose levels within acceptable limits - fluctuation is expected within the system.

I would suggest researching the connections between hunger/intake/digestion/absorption/blood glucose/beta cells/insulin/cell uptake/cell demand/exertion/glucagon/renal excretion of glucose/polyuria/polydipsia
- it's complex.

Biological models systems have much to teach us. If we ask the questions and notice the connections rather than trying to make them fit with our explanation.

You should check out the explanation of insulin/glucose regulation in my review of Design Principles of Biological Circuits.

economic models = made up by humans
physiology = millennia of chance and adaptions under various pressures, creating immensely complex systems that just blow my mind.

Again, read that review. A central point of the book is that evolved systems repeatedly converge on similar patterns, because those are the patterns which work well. Economics, on the other hand, is largely a mathematical discipline studying general properties of things-which-work-well for optimization. Through that lens, it makes a lot of sense to apply economic models to biological systems.

I would suggest researching the connections between hunger/intake/digestion/absorption/blood glucose/beta cells/insulin/cell uptake/cell demand/exertion/renal excretion of glucose/polyuria/polydipsia
- it's complex.
Biological models have much to teach us. If we ask the questions and notice the connections rather than trying to make them fit with our explanation.

Consider this picture:

There's a dog in the picture. Once you see the dog, there's still a lot going on in the picture, but the whole thing makes a lot more sense.

That's what theory is about. It's not "trying to make [reality] fit our explanation", it's about noticing hidden structure. That's the sort of value I expect economic theory would provide in physiology.

The structure of insulin/glucose regulation is the structure of a market. Yes, the system is complicated, and there's a lot of moving pieces - that's true in markets too. But over long timescales, the pieces are interacting primarily through a price signal - insulin - and that's the key characteristic which makes it a market, regardless of whatever else is going on locally. That's a useful piece of hidden structure.

I have read the insulin analogy (I read it before first commenting here).

I don't know if the insulin analogy is from the book itself or your interpretation. But it is flawed. For multiple reasons. I started to pick it apart line by line but then decided a better course of action would be to try pointing you in the right direction - so that you could do the research about the physiological system, learn about what you are trying to label and then consider whether it is a good path to be following.

Does it really make sense to apply economic labels to physiological systems?

That's the sort of value I expect economic theory would provide in physiology.

Expect? Careful that you are not rationalising your beliefs.

Models of physiology are also dynamic man made constructs. Physiology was developed by the world. Similarly with models of economics and economics itself. It seems very likely that there are patterns that naturally occur in both model types. If we can build an understanding of how those patterns influence system dynamics, there is potential is applying that understanding whenever we see that pattern. If we find that the understanding doesn't hold up in the new paradigm then we know our understanding was incomplete and can hopefully use contextual information to reform it. There's nothing special about economics or physiology in this regard and all fields likely contain information useful to other fields.

If you don't believe models of physiology are man made, find any example in history where our understanding of physiology changed through the acquisition of new information. The underlying physiology of humans didn't change in that moment, but our model did.

Model was poor wording on my part at the end, I've changed it to physiological systems. They are not constructs of humans. We create "models" , or 'stories' to explain things.

Physiology is a process of nature - complicated and only partially understood. Economics is artificial.

Patterns are seen in many things. Fractals is a word I'm just going to chuck in to think about. And the Fibonacci sequence. And the world is freaky.

Applying physiological models (they've got pretty good at maintaining equilibrium within a range, and system stability) to economics would potentially be a more productive - if the 'facts' that are known are known and considered.

Human market behavior is also complicated and only partially understood. In particular behavior economics finds that humans do all sorts of decisions that violate the rational actor axiom.

At the same time economic theory can still make useful predictions about the behavior of markets.