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Modeling Neural Networks Paul Nuytten CPSC 607 Outline Why model neural networks? A brief look at the neuron. A look at some current works. Adding an evolutionary strategy. Why Model Neural Networks? The nervous system is a


  1. Modeling Neural Networks Paul Nuytten CPSC 607

  2. Outline  Why model neural networks?  A brief look at the neuron.  A look at some current works.  Adding an evolutionary strategy.

  3. Why Model Neural Networks?  The nervous system is a very complex system with many hidden properties.  Many experiments cannot be performed in vivo without destroying the specimen; leaving many questions unanswered.  When looking at a model many of the redundant structures and processes can be removed leaving a more focused picture.  The nervous system is a very efficient and massively parallel computational device. Models may capture this property to solve a certain class of problems.

  4. The Neuron

  5. The Neuron  The neuron shares many of the same components as many other types of cells.  It’s the unique structures that make the neuron a powerful communication and computational device.

  6. The Neuron  The unique components are  The dendrites  The axon  The synapses

  7. The Dendrites  The dendrites are short strands that protrude from the cell body or the soma.  The dendrites are very receptive to connections from other neurons.  The dendrites carry signals from the synapses to the soma.

  8. The Axon  The axon is a long extension from the soma.  Each neuron only has one axon.  The axon is myelinated if it is insulated with Schwann cells.

  9. The Axon  If the axon is myelinated the action potential will travel much faster.  The axon carries action potentials from the soma to the synapses.

  10. The Synapse  The synapses are the connections made by an axon to another neuron.  When an action potential arrives at a synapse from the postsynaptic cell, neurotransmitter is released into the synaptic cleft.

  11. The Synapse  The neurotransmitter will interact with ion channels on the membrane of the postsynaptic cell causing them to open letting some ions into the cell while letting other ions escape.  A synapse is call excitatory if it raises the local membrane potential of the post synaptic cell.  Inhibitory if the potential is lowered.

  12. What level should be modeled?

  13. Some Current Works  NEURON  GENISIS  Neural Swarm  Evolutionary Artificial Neural Networks

  14. NEURON  NEURON is a simulation environment for neurons and neural networks.  The NEURON simulation allows a user to focus on the biological and biophysical aspects of a neurological system.  Great tool for biologists.

  15. NEURON

  16. GENISIS  GEneral NEural SImulation System  Provides a simulation environment for biologically realistic models.  Very similar to NEURON.  Allows for parallel processing.

  17. Neural Swarm  Uses the concepts of swarm intelligence when creating neurological models.  Still in its infancy.  Instead of designing the network and defining processes in mathematical terms, the network and processes are allowed to emerge from the simple interactions within the system.  The results are then compared to biologically observed results.

  18. Neural Swarm

  19. Evolutionary Artificial Neural Networks  Focuses more on the computational aspect of artificial neural networks (using them to solve problems).  Uses outgrowth and pruning rules to grow a neural network.  Spontaneous neural activity also contributes to the development of the network.  What is nice about this simulation is its ability to apply a genetic algorithm to the above rules and the network’s morphology to specialize the network to a given problem.

  20. Evolutionary Artificial Neural Networks

  21. Evolutionary Artificial Neural Networks

  22. Conclusion  When creating a simulation it is important to identify the level at which to model.  It is also important to identify the target audience and intended use of your simulation.  Start simple and gradually add complexity.  Collaborate.

  23. References F. Bloom, C. Nelson, A. Lazerson. Brain, Mind and Behavior Third  Edition. Worth Publishers, USA, 2001. N. Campbell. Biology Fourth Edition, pages 993-1009. The  Benjamins/Cummings Publishing Company, Inc., Menlo Park, California, 1996. R. Rojas. Neural Networks A Systematic Introduction. Springer-  Verlag, Berlin, 1996. Rust A.G., Adams R., Schilstra M. and Bolouri H. Evolving  computational neural systems using synthetic developmental mechanisms. 2003. http://www.rwc.uc.edu/koehler/biophys/4d.html  http://www.neuron.yale.edu/neuron/  http://www.genesis-sim.org/GENESIS/  http://strc.herts.ac.uk/bio/alistairr/neural_interests.html 

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