Basal ganglia-thalamocortical loop model of action selection (Humphries and Gurney 2002)

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Accession:83562
We embed our basal ganglia model into a wider circuit containing the motor thalamocortical loop and thalamic reticular nucleus (TRN). Simulation of this extended model showed that the additions gave five main results which are desirable in a selection/switching mechanism. First, low salience actions (i.e. those with low urgency) could be selected. Second, the range of salience values over which actions could be switched between was increased. Third, the contrast between the selected and non-selected actions was enhanced via improved differentiation of outputs from the BG. Fourth, transient increases in the salience of a non-selected action were prevented from interrupting the ongoing action, unless the transient was of sufficient magnitude. Finally, the selection of the ongoing action persisted when a new closely matched salience action became active. The first result was facilitated by the thalamocortical loop; the rest were dependent on the presence of the TRN. Thus, we conclude that the results are consistent with these structures having clearly defined functions in action selection.
References:
1 . Humphries MD (2003) High level modeling of dopamine mechanisms in striatal neurons Technical Report ABRG 3
2 . Humphries MD, Gurney KN (2002) The role of intra-thalamic and thalamocortical circuits in action selection. Network 13:131-56 [PubMed]
Model Information (Click on a link to find other models with that property)
Model Type: Connectionist Network;
Brain Region(s)/Organism:
Cell Type(s):
Channel(s):
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s): Dopamine;
Simulation Environment: MATLAB; Simulink;
Model Concept(s): Parkinson's; Action Selection/Decision Making;
Implementer(s): Humphries, Mark D [m.d.humphries at shef.ac.uk];
Search NeuronDB for information about:  Dopamine;
/* general purpose sigmoid:
 * use as template for single input, single output function system (no states)
 */

#define RAND_FACT 2147483647.0	/* largest random number generated */

#define S_FUNCTION_NAME Msigmoid2 /* same as filename */

#include "simstruc.h"
extern double exp();
extern double log();
/* extern long random(); */

/* input arguments (parameters) */

#define SLOPE    ssGetArg(S, 0)
#define THRESH  ssGetArg(S, 1)

/*
 * mdlInitializeSizes - initialize the sizes array
 *
 * for single input, single output function system (no states)
 * notice use of ssSetNumInputArgs() to set number of input pars 
 */

static void mdlInitializeSizes(S)
    SimStruct *S;
{
    ssSetNumContStates(    S, 0);      /* number of continuous states */
    ssSetNumDiscStates(    S, 0);      /* number of discrete states */
    ssSetNumInputs(        S, 1);      /* number of inputs */
    ssSetNumOutputs(       S, 1);      /* number of outputs */
    ssSetDirectFeedThrough(S, 1);      /* direct feedthrough flag */
    ssSetNumSampleTimes(   S, 1);      /* number of sample times */
    ssSetNumInputArgs(     S, 2);      /* number of input arguments */
    ssSetNumRWork(         S, 0);      /* number of real work vector elements */
    ssSetNumIWork(         S, 0);      /* number of integer work vector elements */
    ssSetNumPWork(         S, 0);      /* number of pointer work vector elements */
}

/*
 * mdlInitializeSampleTimes - initialize the sample times array
 *
 * This function is used to specify the sample time(s) for your S-function.
 * If your S-function is continuous, you must specify a sample time of 0.0.
 * Sample times must be registered in ascending order.
 */

static void mdlInitializeSampleTimes(S)
    SimStruct *S;
{
    ssSetSampleTimeEvent(S, 0, 0.0);
    ssSetOffsetTimeEvent(S, 0, 0.0);
}

/* have to have th efiollowing functions even though they are empty 
 * otherwise get segmentation violations */

static void mdlInitializeConditions(x0, S)
    double *x0;
    SimStruct *S;
{
}

static void mdlUpdate(x, u, S, tid)
    double *x, *u;
    SimStruct *S;
    int tid;
{
}

static void mdlDerivatives(dx, x, u, S, tid)
    double *dx, *x, *u;
    SimStruct *S;
    int tid;
{
}

static void mdlTerminate(S)
    SimStruct *S;
{
}

/***************** main function calculation **********/
/*
 * mdlOutputs - compute the outputs
 *
 */

static void mdlOutputs(y, x, u, S, tid)
    double *y, *x, *u;
    SimStruct *S;
    int tid;
{
     double slope, thresh;
     double act;
     double y_out;

     slope = mxGetPr(SLOPE)[0];
     thresh = mxGetPr(THRESH)[0];

     act = u[0];
     if (act <= thresh) {
	  y_out = 0;
     }
     else if ((act > thresh) && (act < 1/slope + thresh)) {
	  y_out = slope * (act - thresh);
     }
     else {
	  y_out = 1;
     }
     y[0] = y_out;

}


#ifdef	MATLAB_MEX_FILE    /* Is this file being compiled as a MEX-file? */
#include "simulink.c"      /* MEX-file interface mechanism */
#else
#include "cg_sfun.h"       /* Code generation registration function */
#endif

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