# Setting up connections with hoc

## Model

A simplified NEURON implementation of the Hopfield and Brody model described in
JJ Hopfield and CD Brody, PNAS 97:13919 (2000)
and
JJ Hopfield and CD Brody, PNAS 98:1282 (2001)

For detailed information about the original model see http://str.princeton.edu/mus/Organism/

## Implementation

The file model_hb_ex.hoc contains the specifications of cells and synapses. The "event times pattern" is read from the exemplar.txt file into the chan[inchan] vector. The cells in the processing layer (alpha and beta) are arranged in an array and, thus, each cell is identified by two indexes. A subset of 30 cells has been preselected to recognize the input pattern. A list of the indexes for these cells is read from the connections.txt file into the index[dimcon][2] array.

## Exercise

Go to the course/hb directory and compile the mod files for the Na+ and K+ conductances that are used in this exercise.

Before running the hb_ex.hoc simulation, edit the model_ex_hb.hoc file to add the hoc code that establishes all-to-all connections among the preselected cells. Look at the NEURON help file for the syntax and parameters for the NetCon() statements, and use the following pseudocode for hints:

    for i=0, dimcon-1 {
        x0=index[i][0]
        y0=index[i][1]
        connect a[x0][y0] with gamma
        connect b[x0][y0] with gamma

        for j=0, dimcon-1 {
            x1=index[j][0]
            y1=index[j][1]

            if (j!=i) {
                connect a[x0][y0] with a[x1][y1]
                connect b[x0][y0] with b[x1][y1]
            }

            connect a[x0][y0] with b[x1][y1]
            connect b[x0][y0] with a[x1][y1]
        }
    }

In model_ex_hb.hoc there are predefined object names that you should use to define the connections :
netga[ ] for alpha -- gamma,
netgb[ ] for beta -- gamma,
netaa[ ] [ ] for alpha -- alpha,
netbb[ ] [ ] for beta -- beta,
netab[ ] [ ] for alpha -- beta,
and netba[ ] [ ] for beta -- alpha.

The connection weights between the preselected cells are initialised before each simulation (look at the run_x procedures in the hb_ex.hoc simulation file).

NEURON hands-on course

Copyright © 2001 by M. Migliore, all rights reserved.