Mental Causation

Primes, wheels, and particle colliders

What is the nature of mental causation? If the mind is not a substance (sorry, Monsieur Descartes), then how does something abstract and intangible exert a causal influence on the physical substance of the brain? How does a thought interact with a neuron? How is it that a fear of abandonment exerts a causal influence on my brain networks? How does an experience of humiliation bring about an episode of depression? How does childhood trauma shape one’s personality?

All forms of so-called “downward causation,” including psychological causation, seem puzzling because when we usually think of causation, we think of direct interactions between physical phenomena: a billiard ball hitting another billiard ball, a domino toppling another domino, a proton exerting force on an electron, a wave interfering with a wave, etc. In contrast, understanding the causal influence of abstractions requires focusing on forms of organization, and the manner in which different forms of organization constrain physical-chemical interactions to generate novel possibilities.

Think of how abstractions such as an unwise “economic policy” can cause the death of organs in the body of a child in a province experiencing famine. Economic policy is not something tangible that directly acts on the organs of a person or something that directly induces a change in the glucose concentration in a person’s blood, analogous to how a magnet induces an electric current in a coil. Economic policy stands for a dynamic configuration, referring to the manner in which the interactions of millions of people are organized and the constraints under which those interactions take place. This collective arrangement determines how access to nutrients is distributed to individuals who constitute this configuration, and ultimately to organs and cells within the individuals.

We can explain events occurring at a very low level by appealing to higher-order abstractions. Humans build powerful particle colliders, motivated by the desire to advance scientific knowledge. Human interests and motivations cause subatomic particles to smash into each other at velocities approaching the speed of light at a particular location on Earth. This is the causal reality of configurations and constraints.

Although there is a lot more to the mind-body relationship than there is to, say, the citizen-government relationship (I’m primarily thinking of the thorny and unresolved matter of “consciousness”), mental causation by itself need not be any more mysterious than economic causation. Both are instances of downward influence in complex configurations of biological processes.

Two authors who appear to understand this with great clarity are Douglas Hofstadter and Terrence Deacon.

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Douglas Hofstadter offers a brilliant thought experiment, dubbed “domino chainium,” in his book, I Am a Strange Loop. He imagines a mechanical computer that computes using chains of dominoes—the dominoes are spring-loaded such that they automatically flip back to an upright position after a brief period if they are knocked down. Chains of dominoes are arranged in this hypothetical computer through bifurcations and joints such that signals in the form of falling dominoes can propagate.

“The basic idea is just that we can imagine a network of precisely timed domino chains that amounts to a computer program for carrying out a particular computation, such as determining if a given input is a prime number or not… Let us thus imagine that we can give a specific numerical “input” to the chainium by taking any positive integer we are interested in — 641, say — and placing exactly that many dominos end to end in a “reserved” stretch of the network. Now, when we tip over the chainium’s first domino, a Rube Goldberg–type series of events will take place in which domino after domino will fall, including, shortly after the outset, all 641 of the dominos constituting our input stretch, and as a consequence various loops will be triggered, with some loop presumably testing the input number for divisibility by 2, another for divisibility by 3, and so forth. If ever a divisor is found, then a signal will be sent down one particular stretch — let’s call it the “divisor stretch” — and when we see that stretch falling, we will know that the input number has some divisor and thus is not prime. By contrast, if the input has no divisor, then the divisor stretch will never be triggered and we will know the input is prime.

Suppose an observer is standing by when the domino chainium is given 641 as input. The observer, who has not been told what the chainium was made for, watches keenly for while, then points at one of the dominos in the divisor stretch and asks with curiosity, “How come that domino there is never falling?”

Let me contrast two very different types of answer that someone might give. The first type of answer — myopic to the point of silliness — would be, “Because its predecessor never falls, you dummy!” To be sure, this is correct as far as it goes, but it doesn’t go very far. It just pushes the buck to a different domino, and thus begs the question.

The second type of answer would be, “Because 641 is prime.” Now this answer, while just as correct (indeed, in some sense it is far more on the mark), has the curious property of not talking about anything physical at all. Not only has the focus moved upwards to collective properties of the chainium, but those properties somehow transcend the physical and have to do with pure abstractions, such as primality…

The domain of prime numbers is as remote from the physics of toppling dominos as is the physics of quarks and gluons from the Cold War’s “domino theory” of how communism would inevitably topple country after neighboring country in Southeast Asia. In both cases, the two domains of discourse are many levels apart, and one is purely local and physical, while the other is global and organizational…

The point of this example is that 641’s primality is the best explanation, perhaps even the only explanation, for why certain dominos did fall and certain other ones did not fall. In a word, 641 is the prime mover. So I ask: Who shoves whom around inside the domino chainium?” (pp. 37-39) (my emphasis)

Domino chainium serves as a power metaphor, and Hofstader refers to it numerous times in the book.

“… the intangible, abstract quality of the primality of the integer 641 is what most truly topples hard, solid dominos located in the “prime stretch” of the chainium. This is nothing if not downward causality, and it leads us straight to the conclusion that the most efficient way to think about brains that have symbols — and for most purposes, the truest way — is to think that the microstuff inside them is pushed around by ideas and desires, rather than the reverse.” (p. 176)

And

“We do indeed have wants, and our wants do indeed cause us to do things (at least to the extent that 641’s primeness can cause a domino in a domino chain to fall).” (p. 339)

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In his remarkable book Incomplete Nature, Terrence Deacon discusses Roger Sperry’s example of a wheel as an illustration of downward causation. Once molecules of a solid substance are arranged in the shape of a wheel, the local constraints on their mobility generate new collective possibilities of movement (such as rolling on a flat surface) that were previously unavailable to those molecules individually.

“For Sperry, the wheel example provides a case of downward causation, because being a part in a particular kind of whole alters possible movement options available to the parts.” (p. 160)

“Sperry uses this analogy to argue that the configuration of brain processes similarly changes what can be done with the parts—the brain’s neurons, molecules, and ionic potentials. But it is a bit of a misnomer to call this a form of causation, at least in modern parlance. The downward (in levels) causation (from whole to part) is in this sense not causation in the sense of being induced to change (e.g., due to colliding or chemically interacting with neighboring molecules), but is rather an alteration in causal probabilities.

This “downward” sort of causality might better be framed in Aristotelean terms as a species of formal cause, whereas the notion of being induced to change (e.g., in position or configuration) might be analogized to Aristotle’s efficient cause.” (p. 161)

A major reason why downward causation puzzles us is because downward causation is not an instance of efficient cause; it is a type of formal cause. (Efficient and formal causes are from Aristotle’s four causes.)

In biological systems, things are far more complicated than in wheels; unlike the components of a wheel, the components of a biological system are not viable outside the system. The integrity of biological components depends on the integrity of the biological whole.

“With cessation of the life of the organism—i.e., catastrophic dissolution of critical reciprocal interrelationships—the components rapidly degrade as well. Thus their structures and resultant properties were in large part derived from this systemically organized dynamic.” (p. 163)

“The wheel can be dissected into its parts and reconstructed without loss, but a living organism taken apart suffers the Humpty-Dumpty problem.” (p. 164)

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The emergent properties of life and mind are the result of new forms of organization of physical-chemical processes, and with new dynamic configurations arise new components that can be further organized in yet higher-order configurations, producing new forms of possibilities in a universe in which everything is ultimately realized by physical interactions of elementary particles.

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Follow-up post:

Mental Causation and Metaphysical Gloss

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See also:

Mark Solms and Sanneke de Haan on the Mind-Body Problem

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