FIGURE 9.2-1 Four nonlinearities relating generator potential (mp) to (analog) instantaneous frequency (r) in the NSL modeling language.

set up the GUI, control the simulations and plot results. Neuron effects the simulation on a molecular and ionic level, using a modified HH approach. It permits both voltage- and current-clamping simulations on active nerve membranes. Axons, dendrites, and soma are modeled as cylindrical sections; they can be sized and connected, and given specified membrane properties (e.g., HH or passive). Synapses are not modeled per se, but the action potential at the end of an axon can be used to activate specific conductance changes on the soma or dendrites of the postsynaptic neuron through point processes. To achieve synaptic connection between a presynaptic axon and a postsynaptic dendrite or soma, the user must write a subroutine in the Neuron MODL modeling language. This process must be performed for each synapse. The delay, size, and time course of the conductance changes producing the epsp or ipsp can be specified in the KINETIC section of the MODL subroutine. When using multiple neurons, their locations are specified in three-dimensional space. The user has a choice of two integration routines to solve the conductance ODEs: backward Euler and a "variant of Crank-Nicholson (C-N)."

The reader interested in learning more about Neuron and what it can do is urged to visit the following web sites: ("What is NEURON?"); (Kevin E. Martin's "NEURON Programming Tutorial"); (Kimberly Spillman's "Beginning with Neuron"); http:/ (N.T. Carnevale and M.L. Hines' digital preprint of "The NEURON Simulation Environment"). Neuron software is located at the anonymous ftp site:

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