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Séminaire Neurocybernétique : Chaos in the brain

Titre du séminaire

Chaos in the brain.

Date et lieu du séminaire

Lundi 19 décembre 2011, de 14h à 16h.
Université de Cergy-Pontoise, site de Saint-Martin 1, 5ème étage, bâtiment A. [plan d'accès]

Pour assister au séminaire, contacter Alexandre Pitti.

Exposés

Cantor sets meet the brain

Ichiro Tsuda, Research Institute for Electronic Science & Research Center for Integrative Mathematics, Hokkaido University

Abstract:

The Cantor set is a set satisfying the following three conditions: it is closed, totally-disconnected and perfect. Its structure gave me a hint to make a mathematical model of the hippocampus which is responsible for the formation of episodic memory. Actually, I found several chaotic behaviors in a model CA3, and also a Cantor set in a model CA1. Based on these findings, I have proposed a hypothesis on the formation of episodic memory. After my predictions, chaotic behaviors at a network level have been observed in hippocampal CA3, and also a Cantor set in CA1. This example suggests a promising relationship between mathematical and experiment studies.

Références:

  • Chaotic Dynamics, Episodic Memory, and Self-identity, in Advances in Cognitive Neurodynamics(II): Proceedings of the Second International Conference on Cognitive Neurodynamics, 2009, eds. R. Wang and F. Gu, Springer (2011) pp. 11-18
  • Hypotheses on the functional roles of chaotic transitory dynamics, CHAOS 19, 015113-1 - 015113-10 (2009)

Why/How people see things that are not there? Brain Viewed from Dynamical Systems

Hiroshi Fujii, Kyoto Sangyo University

Abstract:

Acetylcholine (ACh) is the first substance identified as neurotransmitter by Otto Loewi (1921). Traditionally it is known to work in the brain as the control system of global brain states such as arousal, and transitions between sleep stages as well as sleep-awake alternation. The focus of my talk is, however, not on such global cholinergic control systems, but on higher cognitive functions as attention, conscious flow and so on, the significance of which has been increasingly recognized.

Loss of ACh in the cortex, either due to diseases such as Alzheimer's disease or dementia with Lewy bodies (DLB), or due to pharmacological treatments with an ACh antagonist (such as scopolamine or atropine) causes aberrant cognitive disorders such as deficits of attention(s) and hallucinations (recurrent complex visual hallucinations; RCVH). Here people see things that are not there. They see vivid color images of persons or animals that are not there. Why does just a chemical substance as ACh contribute to such cognitive (mal-)functions?

Seeing things that are not there is, however, an important mental activity, not only in brain's malfunctioning. The brain mechanisms of such internal processes depend essentially on cortical dynamics, and consequently we must rely on dynamical systems viewpoints. Here I would like to introduce some of our recent hypothetical arguments to tackle the questions mentioned above, where the concept of quasi-attractor (attractor ruins) may play the key role. Cortically projecting ACh released in association with conscious attention(s) may in a sense play the role of bifurcation parameter.

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