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OCNC Statistical Approach to Neural Learning and Population Coding Introduction to Mathematical Neuroscience Shun-ichi Amari Laboratory for Mathematical Neuroscience RIKEN Brain Science Institute
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BRAIN biological science information science
Computational neuroscience Neurocomputing Mathematical Neuroscience
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II. Population Coding I. Mathematical Neuroscience ---- modern topics
----classical theories II. Population Coding ---- modern topics III. Bayesian Inference ---- its merits and critique
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Dynamics of Neuro-Ensembles Dynamics of Neuro-Fields
1. Mathematical Neurons Dynamics of Neuro-Ensembles Dynamics of Neuro-Fields Learning and Self-Organization 5. Self-Organization of Neuro-Fields
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I Mathematical Neurons
Simple model
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output function u
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spiking neuron integration-and-fire neuron rate coding
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synchrony : spatial correlations firing probability
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rate coding ensemble coding
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1-layer network
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Ensemble of networks macroscopic state macroscopic law
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stability = =
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Associative memory m pairs
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Randomly generated Random matrix
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II Dynamics of Neuro-Ensembles
spiking neurons : stochastic point process synchronization Ensemble coding : macrodynamics
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Simple examples Bistable S S Multi-stable
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oscillation Amari (1971); Wilson-Cowan (1972)
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competitive model (winner-take-all)
・・・ (winner-share-some)
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multistable associative memory decision process
(Anderson, Amari, Nakano, Kohonen Hopfield) decision process (Hopfield) travelling salesman problem
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General Theory Transient Attractors stable state limit cycle
chaos (strange attractors)
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Chaotic behavior random stable states chaos Chaotic memory search
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Associative memory (content-addressable memory)
dynamics random attractor
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Theory 1 =
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=
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Theory 2 …..
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Macroscopic state Amari & Maginu, 1998
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Dynamics of recalling processes
Direction cosine Correct pattern 1 time simulations
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Direction cosine 1 theory time
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simulation Threshold of recalling Spurious memory
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Dynamics of temporal sequence (Amari, 1972)
non-monotonic output function Morita model
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Nonmonotonic model non-monotonic
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memory capacity : sparse
exact : no spurious memories chaotic oscillation inhibitory connection
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Biology hippocumpus, Rolls et al Chaotic associative memory
Tonegawa et al CA3 Chaotic associative memory Aihara et al Chaotic search
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Associative Memory Dynamics of a Chaotic Neural Networks
Each neuron model shows chaotic dynamics Synaptic weights are determined by an auto-correlation matrix of the stored patterns Stored Patterns t=0 t=1 t=2 t=3 t=4
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t=5 t=6 t=7 t=8 t=9 t=10 t=11 t=12 t=13 t=14 t=15 t=16 t=17 t=18 t=19
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t=20 t=21 t=22 t=23 t=24 t=25 t=26 t=27 t=28 t=29 t
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III Field Dynamics of Neural Excitation
timing local excitations: travelling wave: oscillatory: memory decision Amari, Biol. Cybern,1978
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Dynamics of Neural Fields
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unstable stable
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excitatory and inhibitory fields
traveling wave oscillation
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Neural Learning (Hebbian)
classic theory ……… Information source I
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Amari, Biol,Cybern,1978 Hebbian correlation generalized inverse
principal component analyzer Perceptron ….
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Neural learning (STDP)
Spike-time dependent plasticity …. ……. emergence of synchrony LTP LTD
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Learning Potential ………
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1. Hebbian … 2. correlation associative memory …
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3. generalized inverse least square
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4. principal component analyzer
Amari (1978), Oja (1980) 5. perceptron
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Theory of Learning Networks
Amari, IEEE Trans.C,1967 PDP: backprop; natural gradient
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Learning algorithm
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outer world
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Self-organization …. …….
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Proof RF of a neuron :
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Special case Theorem: each : receptive field size of receptive field
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1.resolution 2.topological property Self-Organizing Nerve Field
signal space neural field 1.resolution 2.topological property
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higher-dimensional 2- dimensional
Topology Signal space Neural field higher-dimensional 2- dimensional position×orientation
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orientation Signal space Neural field position
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Self-organizing nerve field
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dynamical stability patch structure
variational equation stability : Takeuchi&Amari, Biol.Cybern, 35, 63-72, 1979
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Topological properties
emergence of block structure
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Bayesian vs Fisherian. Any confrontation. --- histrical New framework
Bayesian vs Fisherian? Any confrontation? histrical New framework? Amari, New in neuroscience?
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Bayesian framework mle vs map information and decision asymptotically equivalent regularization theory predictive distribution
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Priors: uniform, Jeffreys, smooth Hierarchical (empirical) Bayes decision of prior
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Singular statistical model Singular model and prior
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