From reductionism to dynamical systems

Mike's Notes

"For The Transmitter’s first annual book, five contributing editors reflect on what subfields demand greater focus in the near future—from dynamical systems and computation to technologies for studying the human brain.an article by Nicole Rust on how the brain works." - Transmitter

One of those authors was Nicole Rust who wrote "The field is increasingly embracing the notion that the brain is a “complex dynamical system” where causes lead to effects that feed back as causes—this happens through feedback loops within the brain and interactions between the brain and the environment. From ecology, engineering and other fields, we know that when complex dynamical systems go awry, they can be exceedingly difficult to restore. Tackling that challenge will be the key to developing treatments for the billions of people with brain conditions of nearly every type, from Parkinson’s disease to psychosis." - Nicole Rust Transmitter

That got me curious, so I looked up what else she had written and discovered the article below.

"Nicole Rust is professor of psychology at the University of Pennsylvania in Philadelphia. Her research focuses on understanding the brain’s remarkable ability to remember the things we’ve seen and using that knowledge to develop new therapies to treat memory dysfunction. She is also writing a book on the types of understanding of the brain that will ultimately be required to treat neurological and psychiatric conditions. In it, she argues that effective progress in brain research will require ambitious and unprecedented multidisciplinary conversations of the type that will appear in The Transmitter.

Rust received her Ph.D. in neuroscience from New York University and completed her postdoctoral training at the Massachusetts Institute of Technology. She has been recognized by the Troland Research Award from the National Academy of Sciences, the McKnight Scholar Award, a CAREER Award from the National Science Foundation, a Sloan Research Fellowship, the Charles Ludwig Distinguished Teaching Award, and election to the Memory Disorders Research Society." - Transmitter

Resources

From reductionism to dynamical systems: How two books influenced my thinking across 30 years of neuroscience

By: Nicole Rust
Transmitter: 26 August 2024

I first read Francis Crick’s “The Astonishing Hypothesis,” published in 1994, as a disenchanted undergraduate student. I knew that I wanted to change my major from chemical engineering, but I was unsure about what I wanted to switch to. In Crick’s book, I found the answer in spades. In fact, 30 years later I can still recite key lines from “The Astonishing Hypothesis” from memory: “You, your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules.” Though I wasn’t completely convinced that the hypothesis was correct, the notion that I could make a career out of studying it hit me as a profound insight. I still have my original copy of Crick’s book, complete with a dozen or so Post-it notes marking the most important passages.

I eventually ended up studying vision and memory rather than consciousness per se, but that tattered copy has continued to be influential across my career. I read it most recently a few years ago, when I was contemplating writing a book myself. Though I still very much respect the brilliance of Crick’s book, what struck me on that recent reread was how outdated it had become. I view that not as an indictment but as evidence of the evolution of our field. “The Astonishing Hypothesis” reflects an era of 1990s neuroscience in which researchers shifted toward thinking about the wonders of the brain and mind in ways that were more mechanistic and scientifically falsifiable. That approach tended to try to reduce every phenomenon to a simple explanation, such as the expression of a gene or the activity of a brain area. For instance, Crick proposed that the decisions we make may not be freely decided but instead predetermined, and that our illusion of free will may arise from what happens in the anterior cingulate cortex.

What is the modern alternative? Enter Kevin Mitchell‘s 2023 book “Free Agents: How Evolution Gave Us Free Will,” which reflects a shift toward thinking about the brain as a complex dynamical system with emergent properties that defy reduction to simple elements. In “Free Agents,” Mitchell spells out how will that is truly free could exist in a dynamical brain in which agency has evolved across millions of years. (The Transmitter published an excerpt from “Free Agents” last year.)

The gist of Mitchell’s proposal is that higher-level mental states do not simply emerge from the activation of neurons and their interactions, but that they also influence how brain activity will evolve in the future. In Mitchell’s account, noise allows for multiple possible future brain states, and top-down causal influences determine which one happens. It’s this process that creates free will. A long-held objection to this type of idea is that mental states cannot both emerge from brain activity and also simultaneously cause it, because in that argument, causality is “circular.” Central to Mitchell’s argument is that top-down influences do not act instantaneously but instead shape the future of the system, like a “spiral” that unfolds in time. This provocative proposal has inspired me to think about how we might test ideas about “spiraling” causality—to explain not just free will, but also functions such as seeing, remembering and feeling.

Causality question: Mitchell ascribes free will to a process in which noise allows for multiple possible future brain states, and top-down causal influences determine which one happens. A long-held objection to this type of idea is that mental states cannot both emerge from brain activity and also simultaneously cause it, because in that argument, causality is “circular.” Central to Mitchell’s argument is that top-down influences do not act instantaneously but instead shape the future of the system, like a “spiral” that unfolds in time.

I’m very much looking forward to revisiting Mitchell’s book in 30 years to see how well it holds up. My hope is that we will have either verified that the framework is correct, or (as with Crick’s book) we will regard it as pioneering but dated, and we will have moved on to a better alternative. Either would reflect tremendous progress in our field. I can’t wait to find out.

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