Low-dimensional dynamics in sensory biology 2: Facial cold receptors of the rat

We report the results of a search for evidence of unstable periodic orbits in the sensory afferents of the facial cold receptors of the rat. Cold rece ptors are unique in that they exhibit a diversity of action potential firin g patterns as well as pronounced transients in firing rate following rapid temperature changes. These characteristics are the result of an internal os cillator operating at the level of the membrane potential. If such oscillat ors have three or more degree of freedom, and at least one of which also ex hibits a nonlinearity, they are potentially capable of complex activity. By detecting the existence of unstable periodic orbits, we demonstrate low-di mensional dynamical behavior whose characteristics depend on the temperatur e range, impulse pattern, and temperature transients.