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Earthquakes, Forest Fires, Stars and Brains

Posted By Prucia Buscell, Thursday, April 10, 2014

Human brain activities that give rise to thinking may be akin to the dynamics of earthquakes, forest fires, the spread of contagious disease, the distribution of galaxies in the universe and the sand in an hourglass.

Flip an hour glass upside down, and sand running into the bottom of the glass forms a pile that eventually becomes so unstable that one more grain can cause the pile to collapse into an avalanche. When that happens, the base of the sand pile flattens out, another pile begins, and then it too reaches a point where it collapses. Through several avalanches of varying sizes, the sand pile maintains overall stability. It's a process Danish-American scientist Per Bak called "self organized criticality."

When he died in 2002, The New York Times described Dr. Bak as an "intellectually pugnacious physicist who sought to understand how complexity arises in the world," and how the simple particles that make up the universe could be transformed into the extraordinarily intricate order found in nature. A story by Jennifer Ouellette in Quanta Magazine and reprinted in the Scientific American, explains that Dr. Bak found an answer in phase transition, the process in which materials pass from one state to another. The phase change of water to steam, for example, depends only on temperature and air pressure. Ouellette explains Dr. Bak proposed phase change in which local interactions among many elements of a complex system could spontaneously self organize to reach the tipping point he called criticality. In a 1987 paper in Physical Review Letters, Dr. Bak and coauthors described self organized criticality as the underlying mechanism behind the flow of rivers, the luminosity of stars, and what happens in sand piles and other dynamical systems. His book How Nature Works expands on the idea.

Neuroscientists didn't immediately embrace Dr. Bak's idea on brain function when he proposed it 15 years ago. In the last decade, however, EEG recordings of the interactions among individual brain neurons, large scale studies comparing computer model predictions and fMRI images, and examinations of slides of cortical tissue, have produced evidence that the brain exhibits properties of criticality. Neurophysiologist Dante Chialvo, from the University of California at Los Angeles, is among the renowned scientists who now think self organized criticality could explain brain activity. The idea is also being explored by national and international research efforts.

Getting back to the hour glass. Ouellette explains that when the sand pile-a complex system with millions of tiny elements-reaches the critical point, there is no way to predict which next grain will cause the avalanche, how big any avalanche will be, or how many there will be before all the sand is in the bottom of the glass. The things you can predict are that the falling of one extremely tiny grain can have a big impact; and that while overall stability of the system is maintained-there's still a pile-and there will be more small avalanches than big ones, in line with what mathematicians call power laws.

The exact moment of transition in a phase change is the critical point when the system is half way between one phase and the next. Each of the tens of billions of neurons in our brains, their connections and their interactions, produce "the emergent process we call thinking," the Quanta article says. It goes on to say that Dr. Bak's idea "implies that most of the time, the brain teeters on the edge of a phase transition, hovering between order and disorder."

Tags:  buscell  complexity matters  nature  neuroscience  science 

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