In his seminal work of science fiction, A Hitchhiker’s Guide to the Galaxy, Douglas Adams ponders a question, which turns out, unsurprisingly, to be difficult to answer: What is the meaning of life, the universe, and everything?

In the novel, a super-intelligent civilization builds a super-computer to answer the question. That super-computer cannot answer the question, but thinks it might be able to build a second computer that can. The second computer turns out to be a large-scale simulation: Planet Earth! After running for several million years, Planet Earth (roughly as we know it) provides a very simple answer to the super-intelligent civilization. The answer to the question? Well…

In many ways, the super-intelligent civilization’s quest is a fable for the scientific endeavor. Humankind has sought answers to these fundamental questions through religion, spirituality, philosophy, science.  Even the fact that humanity and life exist on planet earth has been used as a touchstone of metaphysical philosophy: the anthropic principle, which states that the universe must exist in a way consistent with human life; because here we are.

So, here we are. Life, the universe, and everything: an answer in search of a question.

Sometimes the answers generated from these approaches seem simple: an intelligent designer; a virtual reality simulation; the big bang; 42. But scratching the surface reveals inordinate richness, complexity, chaos. No one ever said that understanding the universe was supposed to be easy.

The same has been true of our quest to understand the human brain. Those of you who have been paying attention to our quest to build a theory of the brain realize that there have been no easy answers. But that has not stopped neurophilosophers from developing holistic theories of the brain.

And the progress is stunning.

Drawing on evolutionary theory and natural selection, information theory, neuroscience, philosophy, psychology, and more, a team of researchers led by Paul Badcock published a recent article in the Psychonomic Society’s journal Cognitive, Affective, and Behavioral Neuroscience summarizing a theory of the human brain, cognition, and behavior.  The result is an integrative account of one of the most comprehensive neuroscience theories in the field. I will try to do it justice.

The authors describe a framework they call the hierarchically mechanistic mind (HMM). The overarching ‘design’ principle, Badcock and colleagues argue, is that the brain strives to minimize surprise (or what has been called the Free-energy principle). Through perception, learning, and action, the goal of the neural system is to generate and test predictions. This particular aspect of the process is similar to predictive coding.

For example, consider this illusion. (Do click through to it, it’s worth it.)

The neural system supplies the prediction, based on a model of the world, that the letter A being drawn is a two-dimensional illustration on paper. Yet, the cues to depth are so strong that by the end of the video, the visual system supplies the prediction that there is a very steep drop off in the shape of a letter A that supplants the prediction of a 2D drawing. The original Tweeter captures what Badcock and colleagues are arguing: this hurts your brain.

That the demonstration hurts your brain is illustrative of the authors’ second point: the mind is hierarchical. In other words, it consists of (mostly) modular functional units that have stronger within-module connections than between-module connections, and which are connected in a recursive, self-similar fashion across levels. At the brain level, the authors allude to a rich and growing body of network neuroscience research showing that this sparse modular connectivity pattern is exactly how the brain is organized. Back to our example, the visual system’s prediction of an A-shaped cliff overrides the predictions of higher-level cortices of 2D-drawing; and the tension (and joy) in seeing the illusion consists of the tension of these two functional modules attempting to minimize surprise.

Beyond the hierarchical structure of the brain, the HMM is an evolutionary systems theory. In other words, the same framework that underlies species genetic adaptation – evolution by natural selection – is at play at other levels of analysis. Writ large, this means that various possibilities evolve and then are pruned by some selection process. At the scale of a species, this means things like genes and phenotypes; but this also applies over the course of development where neural structures emerge and are pruned by experience; and finally also in real-time as individuals learn and attend.

Each of these processes is an attempt, so the authors claim, of the neural system of the organism to build a model of the world and minimize the prediction error as a result of the discrepancy between the model and the actual world.

What does any of this have to do with psychology?

The authors argue that the HMM (and the free-energy principle) should guide theory development and hypothesis testing across all levels of psychological science. They demonstrate how the HMM has been applied toward understanding depression as preserving resources in the face of unfavorable social situations. Or, as Badcock and colleagues put it:

“depression instantiates a biobehavioral ‘better safe than sorry’ strategy that causes adaptive changes in perception (e.g., anhedonia and a heightened sensitivity to social risks) and action (e.g., avoidant or cautious social behaviors such as withdrawal).”

Across levels, then, depression is heritable (genetic); stressful periods during early development are associated with increased risks for depression (developmental); adolescence is a critical period for depression to manifest (ontogenetic); and immediate social settings correlate with risk for depression (real-time). The authors formulate depression in terms of the free-energy principle as a period of high social uncertainty, at which point the individual minimizes surprise by avoiding interactions.

The life, the universe, and everything is, as the authors describe, ‘burdened by complexity.’ We will never arrive at an answer to the human brain’s puzzles as simple as 42; yet such an answer would be unsatisfying in most respects, too dismissive of the nuances which guides so much of our theory-building.

For now, I applaud the efforts of Badcock and colleagues who are helping pave the way for a broad theoretical foundation of the field.

Reference for the article discussed in this post:
Badcock, P. B., Friston, K. J., Ramstead, M. J. D., Ploeger, A., & Hohwy, J. (2019). The hierarchically mechanistic mind: an evolutionary systems theory of the human brain, cognition, and behavior. Cognitive, Affective, & Behavioral Neuroscience. DOI:10.3758/s13415-019-00721-3.