Generating a unit impulse function

Hey all,

I have a function which:

function xprime=nagumo(t,x,i);
a=i(1); %CONTROL LOCATION AT WHICH PULSE OCCURS
b=i(2);
xprime=[x(1)-(1/3)*(x(1))^3-x(2)+***INSERT UNIT IMPULSE***;0.08*(x(1)+0.7-0.8*x(2))];

I need to use this nagumo function with ode45 in the form:

 [t,x]=ode45(@nagumo,tspan,x0,[],i);

I need the unit impulse to be a signal as a time series with at least two time samples as being 1, and the rest of the samples being zero. Which is basically a rectangular pulse, occuring only once at the t i specify for the duration I specify. The height of the pulse is 1.

Thanks