How to only use 2 of my 4 cores (intel i5) to train neural network?

I tried following codes to train NN. But instead of using 2 cores, the train() still uses 4 cores because I can see all of my 4 cores are running high in the Windows 7 task manager. How do I use only two cores to train NN? So that I can use the rest of two cores to do something else?

%%%%%%%%%%%%Code starts
N=2;
myCluster=parcluster('local'); myCluster.NumWorkers=N; parpool(myCluster,N)

net2 = train(net1,x,t,'useParallel','yes','showResources','yes');
y = net2(x,'useParallel','yes','showResources','yes');

Answer 1

[Edric Ellis]

I tried the following:

N=2;
myCluster=parcluster('local'); 
myCluster.NumWorkers=N; 
parpool(myCluster,N)

[x,t] = vinyl_dataset;
net = fitnet(140,'trainscg');

net2 = train(net,x,t,'useParallel','yes','showResources','yes');

and did not see any excessive CPU usage - the two MATLAB workers each used a single CPU. (I tried in R2015a on both Windows and Linux)...