Cortical spreading depression (Leão 1944) is a slowly propagating (~3 mm/min) wave of near-complete depolarization followed by silence, underlying migraine aura and stroke penumbra. Modeled as a FitzHugh-Nagumo reaction-diffusion system: potassium floods out, glutamate releases, triggering neighboring neurons, while a recovery variable enforces a refractory period. Click the canvas to initiate a wave.