Inhibitory Background Field Hypothesis Generated by Gap Junction-Coupled Interneuron Systems in the Neocortex

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The presence of multiple systems of inhibitory interneurons, densely coupled by gap junctions, i.e., electrical couplings, has been known. We studied possible dynamics of such GJ-coupled interneuron systems, and their functional roles in perception and cognition. We reported before that a system of "class I" neurons, with a particular nonlinearity, may exhibit extensive spatio-temporal chaos together with transient synchrony among neurons' spike firings. We give a mathematical characterization of the nonlinear structure of such a neuron class, and call them class I*. We studied the dynamics of such class I* systems, and showed the possibility that a non-classical attractor of Milnor type may control the whole dynamics.We argued that the phenomenon of transient synchrony, appeared in accordance with perceptual bindings in the real brain, could be explained as a phenomenon caused by the inhibitory background field organized by some GJ-coupled interneuron system(s), and which organizes th … More e pyramidal neuron system in relation to generations of functional cell assemblies and dynamic perceptual bindings.We presented also the dynamical systems-theoretic concept of memory based on the Milnor attractor, which may extend and found a basis of the concept of chaotic itinerancy in memory dynamics originally presented by I. Tsuda. As an application of our Milnor theory of memory in the brain, we presented a new hypothesis on the functional relevance of depolarizing GABA_A actions in cortical interneurons. In fact, although GABA is known as the principal mediator of inhibition, there exist numerous report that GABA may play an excitatory role under some conditions even after developmental period. We theorized that such "depolarizing" GABA actions may serve to temporarily invoke attractor-like memories when extensively activated by, e.g., top-down signals, while an ongoing background state of GABA changes its action to inhibition, returning the dynamical nature of the memory back to attractor ruins. Less