dt=0.0001;
t=0:dt:5;
ntrials=10;

figure(1)
cumspikes=cumsum(spikes,2);

plot(t,cumspikes)

sqrcumspikes=cumspikes.*cumspikes;

meanN=sum(cumspikes)/ntrials;
sqrN=sum(sqrcumspikes)/ntrials;

figure(2)
subplot(3,1,1)
plot(t,meanN)
subplot(3,1,2)
plot(t,sqrN-meanN.*meanN)
subplot(3,1,3)
plot(t,(sqrN-meanN.*meanN)./meanN)