place_cells.cpp

/*
	Place cell functions

	One modification to note compared to original formulas this work is
	derived from is that boundary cell input to place cells is limited to
	a local region around the active place cell. This prevents boundary cell
	signal from simply making an increase in signal of all place cells 
	indiscriminately.
*/

double get_distance(int x1, int y1, int x2, int y2, char pd, P *p) {
	// d = sqrt((e_x - i_x - o_x)^2+(e_y - i_y - o_y)^2)
	double x2_x1 = (x2 - x1);
	double y2_y1 = (y2 - y1);
	double half_point = p->x_size / 2; // layer length divided by 2

	// preferred direction bias
	if (pd == 'u') {
		y2_y1 = y2_y1 - 1;
	}
	if (pd == 'd') {
		y2_y1 = y2_y1 + 1;
	}
	if (pd == 'r') {
		x2_x1 = x2_x1 - 1;
	}
	if (pd == 'l') {
		x2_x1 = x2_x1 + 1;
	}	

	// torus wrap around
	if (abs(x2_x1) >= half_point) {
		// distance wraps half way around
		x2_x1 = (p->x_size - abs(x2_x1));
	}
	if (abs(y2_y1) >= half_point) {
		y2_y1 = (p->y_size - abs(y2_y1));
	}

	double d = sqrt(pow(x2_x1,2)+pow(y2_y1,2));

	return d;
}

double pc_rate(double d, P *p) {
	double rate = 0;

	if (d < p->dist_thresh) { // skip calculation for too distant neurons for computational efficiency
		rate = p->pc_level * exp(-((pow(d,2))/(2*pow(p->pc_sig,2))));
	}

	return rate;
}

void place_cell_firing(CARLsim* sim, P *p) {
	/*
		generate place cell firing
	*/
	double pc_current, bc_firing, theta_mod, phase_prec, d;
	int gc_i; 

	for (int p_y = 0; p_y < p->y_size; p_y++) {
		for (int p_x = 0; p_x < p->x_size; p_x++) {
			// find firing
			pc_current = 0.0;
			if (p->pc_active) {
				d = get_distance(p_x, p_y, p->bpos[0], p->bpos[1], 'n', p);
				pc_current = pc_rate(d, p);
				phase_prec = (PI/2) * (d + 1);
				theta_mod = (sin((((PI*2)/p->theta_freq)*(p->t))+phase_prec))/2 + 1;
				pc_current = pc_current * theta_mod;
			}

			// add boundary cell input
			/*
			if (p->bc_to_pc) {
				bc_firing = bc_for_pc(p_x, p_y, cb_x, cb_y, p);
				pc_current = pc_current + bc_firing;
			}
			*/

			gc_i = (p_y * p->x_size) + p_x;
			p->pc_activity[gc_i] = pc_current;
		}
	}

	sim->setExternalCurrent(p->CA1_Pyramidal_Group, p->pc_activity); // apply computed pc current levels
}