Herbstakademie Wildbad Kreuth 2007 (19.8.07/Tsch)


Walter J. FREEMAN Berkeley (USA)

A far-from-equilibrium thermodynamic model of the action-perception cycle based in nonlinear brain dynamics

Cognitive neurodynamics describes the process by which brains direct the body into the world and learn by assimilation from the sensory consequences of the brain-directed actions. Repetition of the process constitutes the action-perception cycle by which knowledge is accumulated in small increments. Each new step yields a freshly constructed frame that is updated by microscopic input to each of the sensory cortices (Freeman, 2004a,b). The continually expanding knowledge base is embodied in attractor landscapes in each of the cortices. The global memory store is based in a rich hierarchy of landscapes of increasingly abstract generalizations (Freeman, 2005). At the base is the landscape of attractors for the primary categories of sensory stimuli in each modality, for example, the repertoire of odorant substances that an animal can seek, identify, and respond to at any stage of its lifelong experience. Each attractor is based in a Hebbian cell assembly of cortical neurons that have been pair-wise co-activated and sculpted by habituation and normalization (Freeman, 1975). Its basin of attraction is determined by the asymptotically expanding subset of receptors that has been accessed during learning. Convergence in the basin to the attractor gives the process of abstraction and generalization to the stimulus category. This categorization process holds in all sensory modalities (Freeman, 2006). The convergence to and holding of a cortical state by an attractor provides a frame of cortical activity that typically includes the entire primary sensory cortex and lasts about a tenth of a second. The action-perception cycle includes 3-6 frames that repeat at rates in the theta range (3-7 Hz). A nonequilibrium thermodynamic model describes how frames form by phase transitions between receiving and transmitting phases in bistable cortex. The marker for the phase transition is a discontinuity in the analytic frequency of the carrier oscillation of the pattern frames.


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