Isabella
 Here would be my method for simulating Matt's rendering effect:
  1. Download the attached shader "overlay_surface.txt"
  2. Put this file in MRIcroGL's "shaders" folder (for Mac users: click on MRIcroGL.app, click on the Finder "gear" icon and choose "Show Package Contents", then go to the Contents/Resources/shaders folder).
 3. Restart MRIcroGL - notice the "overlay_surface" shader now appears in the shader menu - select this for the effect. Note that the "overlayOpacity" and "overlayDepth" sliders allow you to control the translucency of the overlay on the background and the search depth for finding activity beneath the surface of the brain.
 4. You can use the shader interactively through the graphical interface, but if you choose the View/Scripting menu item you can paste the script below into the scripting window and choose Script/Run from the scripting window to showcase the shader:

begin
resetdefaults;
loadimage('mni152_2009_256');
overlayload('motor');
overlayminmax(1, 1.6, 4);
overlaycolorname(1, '5redyell');
overlayload('motor');
overlayminmax(2, -2.6, -4);
overlaycolorname(2, '2winter');
shadername('overlay_surface');
cutout(0.0, 0.5, 0.5, 0.5, 1.0, 1.0);
backcolor(255, 255, 255);
end.