How to Obtain a Portion of an n-dimensioned Matrix

I have a 6 dimensional matrix with dimensions 16x20x22x6x3x13. I identified specific elements of that matrix with the following:
y = find(spec_neg(:,:,:,:,:,1) ~= 0);
Since y is now the indices of the spec_neg and I would like these in matrix subscript form, I determined the subscripts by doing the following:
[i,j,k,l,m,n] = ind2sub([16,20,22,6,3,13],y);
and then concatenated these subscripts into matrix form:
y_ind = cat(2,i,j);
y_ind = cat(2,y_ind,k);
y_ind = cat(2,y_ind,l);
y_ind = cat(2,y_ind,m);
y_ind = cat(2,y_ind,n);

I want to obtain the values of spec_neg that correspond to the subscript values of y_ind but when I do the following:
spec_neg(y_ind)
I get all zeros so that is obviously not the values in y.

What am I doing wrong?