This animation explains the difference between spreading depolarization and spreading depression of activity in the electrocorticogram. In order to simplify this, we look at the recordings from a single electrode, rather than several adjacent electrodes. This means that we cannot see the actual propagation of both phenomena and therefore, we refer to them as "spreading" depolarization and depression, respectively.
Illustration: Judith Carnaby http://www.judithcarnaby.com/
Animation: Sam Muirhead http://www.cameralibre.cc/