This is the keynote address and talk 3 (of 31) at the Conference on Brain Network Dynamics held at the University of California at Berkeley on January 26-27, 2007. Speaker is Walter J Freeman, Department of Molecular & Cell Biology, University of California at Berkeley, Berkeley, CA 94720. http://sulcus.berkeley.edu/
Slides for this talk (with transcript!) are available in both PDF and Powerpoint format from the All files section on the left, or click pdf [6.2MB] or ppt [12MB].
Abstract:
Fifty years ago EEG was widely regarded as noise, the roar of a crowd. It still is, advisedly, because cortical neurons form great crowds, and the task of systems neuroscience is to comprehend them. I perceived EEG as an opportunity to make a contribution. I chose to study three-layered allocortex in the olfactory system as simpler than neocortex yet closer to the senses than the hippocampus. I began by pulsing it with pairs of electric shocks in order to identify a small-signal near-linear range, in which I could model the dynamics with linear equations. From the patterns of relaxation on perturbation — evoked potentials — I modeled the system with differential equations, evaluated the parameters, solved them to simulate the evoked potentials, and deduced the mechanisms of stabilization. I summarized 20 years of linear analysis in my 1975 book, from which I concluded that I had reached the limits of linear analysis. Trying to understand brain function that way was like trying to cross an ocean in a dugout canoe. I conceived a boundary in the imaginary axis of the complex plane. Contemplating that, I felt as Isaac Newton felt, playing with pebbles on a seashore.
In the following 30 years I have explored the design of foundations for ocean crossings. You will hear five promising approaches in this Conference on Brain Network Dynamics. Steve Bressler will describe nonlinear metastability in terms of basin-attractor theory deriving in part from Hermann Haken’s synergetics. Robert Kozma will describe phase transitions in terms of neuropercolation, which he derives from random graph theory. Bert Dreyfus will describe the isomorphism he perceives between brain dynamics and the phenomenology of Martin Heidegger and Maurice Merleau-Ponty. Giuseppe Vitiello will describe the mapping of dissipative brain dynamics into quantum field theory, stemming from the pioneering work of Ricciardi and Umezawa. I will try to show how to map solution sets of nonlinear differential equations into a phase portrait in the self-organizing, far-from-equilibrium thermodynamics that leads from disorder to order: Ilya Prigogine’s ‘dissipative structures’ that feed on energy.
None of these five tools can be used alone with full success; each approach contributes necessary insights. Together they provide a launch pad for vehicles that will carry us arduously but freely to new discoveries across the ocean of nonlinear brain dynamics before us. Like other true explorers, we don’t know what we will find, and we don’t yet have the proper framework in which to describe whatever is there. This broad view from an open mind is my legacy.
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