Posted tagged ‘Emergence’

Emergence and a Flock of Neurons

April 3, 2015

Dan Scherlis just sent me a short video showing starlings in flight,starlings in flight taken at 600 FPS. This fascinating video led me to think about emergence (never far from my mind) and ultimately to recent work in brain organization, or what’s known as the “connectome.”

Videoing the birds at a fast speed enabled the videographer to mark out the path of each bird.This showed how the path and “personal space” around each bird evolved, and thus how the flock formed and reformed over a period of just a few seconds.

Flocking is well-known as a beautiful example of emergence. A flock may be enormous and create complex shapes, from the signature flying-V of geese to dynamic abstract shapes that change moment by moment. One of the amazing things about flocks is that they arise from three very simple rules:

  • Don’t hit any bird near you (keep your personal space)
  • Go in about the same speed and direction as the birds nearby
  • Steer toward the center of mass of birds near you

That’s it! With those three rules and no central coordination, incredible dynamic flocks of birds (and schools of fish, etc.) appear (you can see a simple demo of this, complete with code, here).

Emergence
We say phenomena like this are emergent because a new level of organization appears that has no direct reference to its components. In the case of birds, no bird is the “flock master.” Nowhere is there a plan for what they flock will look like at any given time; the “flock-ness” simply emerges on its own from the autonomous behavior of the individual birds in it.

This points out how you can tell when something is emergent, as so many interesting structures and behaviors are: not only are they driven by individual-but-connected behaviors of their constituents and not by central control, but they also create a structure that is more easily described as a whole rather than as the sum of its parts. it’s much easier to sketch or describe what a flock looks like as a flock than it is to give the same description by noting the precise position and direction of each bird in it.

To use another well-known example, Conway’s “Game of Life” plays out on a 2D grid in which any cell can be “alive” (occupied) or “dead” (vacant). The game consists of just a very few rules:

  • Any live cell with fewer than two neighbors dies (loneliness)
  • Any live cell with more than three neighbors dies (overcrowding)
  • Any live cell with just two or three neighbors lives on happily into the next turn
  • Any dead (vacant) cell with exactly three neighbors comes to life (reproduction)

Despite the simplicity of these rules, this game is well known for creating marvelously complex patterns. Perhaps the most famous is the “glider,” which appears to walk its way across the grid:Game_of_life_animated_glider While the shape itself, the “glider-ness” is persistent, each of the cells making up the glider changes over time. In one sense, there is no glider, since it is made up of individual cells turning on and off based on rules that have nothing to do with “making a glider” or any other shape. But the glider is nevertheless describable as a thing, an object that can be defined without reference to the rules the cells themselves are following. As with any emergent phenomena, it’s easier (more parsimonious) to describe the glider on its own — for example, as “moving down and to the right” against the background — than it is to describe the individual interactions between each of the cells turning on or off with each time step.

From Flocks to Brains
Which brings me back to the starlings above, and from there to neural organization. The birds flock together, moving and forming and reforming moment by moment, as we have all seen. But in the video above the addition of their “flight lines” gives them, and the flock they form, a persistence we don’t typically see.  Image by Jason D.Yeatman in Yeatman et al., Nature CommunicationsMRI diffusion map by Stephen Rose, University of QueenslandWhen I saw this, it immediately reminded me of some other images that have been appearing over the past several years of the “connectome,” — the “wiring plan” for the brain.

These images show the pathways of neurons in the brain — the parts of neurons in the cortex that connect to other parts of the brain, enabling thinking. Without taking a deep dive into the science of neural development and how individual neurons “find their way” from the deep core of the brain to the cortex during early development, the similarities between these pathways and those of starlings in flight is at least superficially apparent.

I suspect these similarities point us to the deeper corresponding processes in each case, and thus to the resulting emergent structures: the here-and-gone flock, and the somewhat more persistent brain — and mind — of each human.

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