criticality

After a long hiatus, I am back to blogging.

Yesterday's physics colloquium was given by Bill Bialek, physicist and theoretical biologist at Princeton (and the PhD thesis advisor of my PhD thesis advisor). His talk was based on a recent paper titled "Are biological systems poised at criticality?". In the context of neuroscience, Bialek's basic observation is that, yes, neural systems appear to have this special "critical" property.

In particular, the observed correlations between the activities of two neurons are such that, if they were any stronger, the brain would be epileptic (recall that, in epileptics, the activities of neurons are amplified such that you get huge cascades of activity, resulting in seizures), but if those correlations were any weaker, the brain would effectively be "dead" (there would be no significant collective behavior).

Now, Bialek's work also discusses criticality in protein sequences, and collective animal behavior, but my interest is mainly in the brain.

Now, from a purely functional standpoint, this "criticality" seems to be sensible, and I could imagine it arising as a product of evolution; animals with more strongly correlated neurons would be epileptic, and they would die off, but so would those with less strongly correlated neurons, as they might be unable to effectively process information.

However, the brain is not static over the lifetime of the animal. We learn and adapt, and as we do, the correlations between neurons in our brains change.

How, then, is this criticality maintained? In other words, is there some kind of homeostatic mechanism that adjusts the correlations (or synaptic connection strengths that, presumably, alter these correlations), to keep them at this critical point?

These are, admittedly, ill-formed ideas at present, but I may very well get back to them when I have a chance.

In other news, my first biology paper was just accepted for publication in "frontiers in computational neuroscience." I will post a link to the paper when it is all copy edited and ready for public consumption.