Faculty Research Page

Walter Freeman

Walter Freeman

Professor Emeritus of Neurobiology*
*And Member, Graduate Group in Biophysics, Graduate Group in Bioengineering

Lab Homepage: http://sulcus.berkeley.edu/

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Research Interests

My research is on analyses of measurements of electroencephalographic (EEG) and unit activity patterns in cortex that occur during goal-directed behavior. Behaviorally relevant information is expressed in spatial patterns of amplitude modulation of gamma waves (20-80 Hz in rabbits, 35-60 Hz in cats, 25-55 Hz in humans) that are triggered in the cortex by input from receptors. The patterns recur like frames cinematographic frames at rates in the theta range (2-7 Hz). Behavioral testing has shown that amplitude patterns of gamma activity are invariant with respect to learned odor stimuli, but change with context and reinforcement under conditioning. The same algorithms hold for olfactory, visual, auditory and somatic cortexes. These spatial patterns are shaped by inputs from the limbic system in the form of corollary discharges, as the basis for attention and expectancy, and by the history of experience with stimuli that is embedded in the cortical neuropil by synaptic modifications that accrue in learning. I conclude that the patterns manifest not the features of stimuli, but the meaning of the stimuli for the animals as an expression of their knowledge base. I model the dynamics of the cortex by networks of nonlinear differential equations. The solutions to these equations show landscapes of equilibrium, limit cycle and chaotic attractors, which I display with interactive graphics. The models sumulate the most essential functions of sensory cortex: abstraction, generalization, and classification.

Selected Publications

How Brains Make Up Their Minds. [W. J. Freeman (2001) New York: Columbia University Press]

Neurodynamics; An Exploration of Mesoscopic Brain Dynamics. [W. J. Freeman (2000) London UK: Springer-Verlag]

Biocomplexity: Adaptive behavior in complex stochastic dynamical systems. [W.J. Freeman, R. Kozma, P. Werbos (2001) BioSystems 59: 109-123]

Chaotic resonance: Methods and applications for robust classification of noisy and variable patterns. [R. Kozma, W.J. Freeman (2001) International Journal of Bifurcation and Chaos 10: 2307-2322]

A neurobiological theory of meaning in perception. Part 1. Information and meaning in nonconvergent and nonlocal brain dynamics. Int. J. Bifurc. Chaos 13: 2493-2511. [Freeman, W.J. [2003a]]

A neurobiological theory of meaning in perception. Part 2. Spatial patterns of phase in gamma EEG from primary sensory cortices reveal the properties of mesoscopic wave packets. Int. J. Bifurc. Chaos 13: 2513-2535. [Freeman, W.J. [2003b]]

Spatial spectra of scalp EEG and EMG from awake humans. Clin. Neurophysiol. 114: 1055-1060. [Freeman, W.J., Burke, B.C., Holmes, M.D. & Vanhatalo, S. [2003]]

Origin, structure, and role of background EEG activity. Part 1. Analytic amplitude. Clin. Neurophysiol. 115: 2077-2088. [Freeman W.J. [2004a]]

Origin, structure, and role of background EEG activity. Part 2. Analytic phase. Clin. Neurophysiol. 115: 2089-2107. [Freeman W.J. [2004b]]

Origin, structure, and role of background EEG activity. Part 3. Neural frame classification. Clin. Neurophysiol. 116: 1117-1129. [Freeman W.J. 2005]]

Last Updated 2005-08-31