Dispersion relation of spreading depression waves in the chicken retina

To describe the spatio-temporal patterns of excitable media, the relationship between frequency and propagating velocity of a wave (dispersion relation) is an important issue. Spreading depression (SD) waves in the brain and especially in the retina are an example of self-organized waves in excitable media (here in neuronal tissue). In the retina such waves are accompanied by a remarkable intrinsic optic signal (IOS), which allows to study the wave by standard video imaging techniques. In this study the dispersion relation of SD waves was investigated under different conditions. As expected from standard theories of excitable media, the velocity is a monotone function of the repetition rate, i.e. of the recovery state, with an absolute refractory phase of about 2.4 min. By increasing the temperature, the shape of the curve changes in a significant way. Physiological and theoretical considerations are given for the variation of the dispersion relation.