Criticality and the brain

Brain connections

Our understanding of how various parts of brain function is advancing at breakneck speed and yet we are as far away as ever from an overarching “theory of the brain” that attempts to encompass these discoveries. Such a theory would unite disparate discoveries in brain science under a unifying theme.

Now Dante Chialvo from Northwestern University in Chicago and colleagues attempt to do just that. Their proposal is that the brain is spontaneously posed at the border of a second order phase transition, just like the transition a ferromagnetic material undergoes as it swtches from a non-magnetic to a magnetic phase.

One of the features of these transitions is the existence of a critical point in which both phases exist simultaneously in a way that ensures that the distinction between them more or less disappears. At this so called “criticality”, all kinds of curious phenonena have been found, including self organising behaviour.

Chialvo and buddies say “all human behaviors, including thoughts, undirected or goal oriented actions or any state of mind, are the outcome of a dynamical system at or near a critical state.”

They make a list of features that they would expect the brain to demonstrate in experiment were it operating close to criticality.

At large scales, they say, we should see cortical long range correlations in space and time as well as large scale anti-correlated cortical states. That certainly seems to be true of our brains in general.

And at small scale, we should see “Neuronal avalanches”, as the normal homeostatic state for most neocortical circuits. And sure enough, the group point to evidence for this.

The trouble is that these look very much like an after-the-fact- predictions in this paper, a feeling that is backed up by the absence of any testable hypothesis about the brain.

If the brain is close to crticiallity (which doesn’t seem like too far fetched an idea), surely it would be possible to make some predictions about the results of experiments such as those involving human attention, optical illusions and the reaction to various stimuli.

So while Chialvo’s proposal may make the pretense of being a theory of the brain, to my mind they’ll have to settle for the status of “interesting idea” until somebody takes them significantly further.

Ref: The Brain: What is Critical about It?

4 Responses to “Criticality and the brain”

  1. DC says:

    Thanks for commenting on the paper. I can appreciatte the comments, and I would like to add that it is incorrect to assume that the proposal contains after-the-fact predictions.

    Indeed the paper recollects the natural sequence of results since Chialvo and Bak first propossed the idea that the brain is critical. The late Per Bak in his book, dedicated a chapter in 1997. As earlier as 1998, Chialvo and Bak discussed in their papers about “Could it be that the brain operates at a critical state, just as the sand models? Already, Turing has speculated that perhaps the working brain needs to operate at a barely critical level, to stay away from the two extremes, namely the too correlated subcritical level and the explosive supercritical dynamics.”

    The impression that the propossal is a convenient after-effect of others published results is baseless. Contrary to that, for instance, the experiments done by Plenz and colleagues describing -for the first time-neuronal avalanches consistent with criticality, were extensively discussed with Chialvo as well, as it is specifically aknowledged in Plenz papers.

    Furthermore, the most recent fMRI experiments (Baliki et al 2008)showing a balanced correlation-anticorrelations in healthy conditions and disrupted in chronic disease is another result guided by these ideas.

    Thus, it is clear that these results are experimental findings motivated by a theoretical idea born outside of mainstream brain science, which long preceded the experiments.

    No one claimed that propossing that the brain is near a second order phase transition is all we need to undestand how the brain works, but it suggest an angle that seems productive, which is inspiring for a number of people.
    And that it already a lot.


  2. Zephir says:

    The finding presented in the article is interesting even in context of Aether Wave Theory (AWT), which considers the vacuum as a critical system, composed of foamy density fluctuations (“strings” and “(mem)branes”) like condensing supercritical fluid. This view is consistent with the idea, the current Universe generation is formed by interior of superdense star, similar to black hole. After then the relevant question arises: which structure of such dense particle system should enable an illusion of the most large space-time as possible for us?

    Well, during supercritical fluid condensation it’s just the critical state, when the density fluctuations are formed and interconnected already, but they’re still not separated into compact droplets, i.e. it has a structure of both fluid, both gas.

    Such system can spread most energy at the distance, thus creating space-time and its behavior is the most complex as possible under given circumstances, because it has a behavior of nested quantum foam, which enables the most advanced evolution inside of such system. This is because every foam gets more dense after introducing of energy like soap foam shaken and the resulting density fluctuation (particles) have an ability to grow and evolve, while focusing the energy waves and collecting another density fluctuations from its neighborhood like food.

    In analogy with this the massive bodies composed of particles are behaving like live critters, which are collecting the another massive objects due their gravitation under gradual formation of more dense and complex systems, thus enabling the evolution of more and more complex structures.

    The Oparin theory considers, the living cells have formed from the coacervate foam on the surface of primeval oceans and the tissue of living organism can be considered as a system of critical density, because it has an structure of foam. Therefore its quite logical, even the structure of neuron network has an structure of foam and the system of electrochemical excitations inside of such system would behave like critical quantum foam as well (compare the Penrose theory of quantum consciousness). From this point of view we can say, the human brain is kinda Universe simulator, which has an apparent ability to simulate (“realize”) itself.

  3. KFC,
    I confirm that Chialvo and Bak suggestion in the nineties provided the heuristics for our work (the Nature Physics paper cited by Chialvo). And, as you can check, we also have discussed possible experimental tests of our theory, for example that mitral cells will display smaller dynamic range if gap junctions in their glomeruli are blocked.

  4. KFC says:

    Thanks guys. It’s a fair cop.