Spiral waves, organizers of temporal and spatial order in excitable media.

The notion "excitable medium' appears to be a unifying concept for the description of a class of wave phenomena observed in many fields of research, from material science to medicine. The analysis of the spatio temporal organization in excitable media reveals that significantly different time series of local activity at various sites may have a common origin in cooperative dynamic excitation structures; rotating spirals. A spiral-shaped pattern emanates from a small organizing center, the core of the spiral. The motion of the spiral tip within the core determines the frequency and the wavelength of a spiral and the peculiar filter properties of an excitable medium allow for the formation of regular spirals even in the case of an highly irregular motion of the tip. Computer-assisted video techniques are recommended to measure these intimate neighbourhood of regular and irregular time-space structures in living matter.