how can I plot topographic map for EEG signal?

I have two EEG channels in CSV format,I would like to see their topographic map for finding frequency distribution over head.Does any one know how it work?

[Borzou Alipourfard]

Hi Samaneh, For a topographic map of brain activity first you need to read your electrode locations( you can find electrode coordinates here:http://sccn.ucsd.edu/wiki/Channel_Location_Files ). Put these coordiantes in a matrix XY . With the data you have recorded, for example alpha activity at each electrode, you now have three column vectors, x, y and z corresponding to coordinates and the activity of each electrode. These set of vectors give you a scatter plot in 3D. To see the topography you will have to define an interpolate function using the following command:

if true
  vq = TriScatteredInterp(X,Y,Z);
end

Now you can use this function on a mesh and plot the response:

if true
ti = -.6:.05:.6;
[qx,qy] = meshgrid(ti,ti);
qz = vq(qx,qy);
mesh(qx,qy,qz);

Using this method for example I can get the following topography for brain activity during a blink.