Spreading cortical depression (SCD) is a wave of depolarization that spreads across the cortex at 2-5 mm/min and is followed by a 5-10 minute reduction in EEG activity. It is assumed that SCD is involved in the pathophysiology of migraine. We present a new model and a visualization technique for the spread of excitation on realistic brain surfaces. The usefulness of the technique is demonstrated on a rat brain that had been segmented from a three-dimensional magnetic resonance image data set. With the help of this methodology it is possible to create specific patient models to better understand the mechanisms of SCD.