Nonlinear cascade analysis of sensory transduction in a mechanoreceptor

Sensory transduction in the cockroach tactile spine can be represented as a single-input single-output nonlinear dynamic process. The major dynamic features of transduction in this receptor are produced during the encoding of action potentials from the receptor current. We have used a new functional expansion method to characterize the dynamic behavior of the tactile spine. This method, which yields similar kernels to the Wiener method, is efficient enough to obtain reasonable kernels in about one hour using a personal computer. The input stimulus was band-limited white noise and the output consisted of action potentials, which were unitized to give binary values. The kernels and the system input-output were used to identify a model for transduction comprising a cascade of dynamic linear, static nonlinear, and dynamic linear components. The two dynamic linear components had repeatable and distinctive forms with the first being low-pass and the second being band-pass. The static nonlinearity was fitted with a fifth-order polynomial function over the input amplitude range and had the form of a half-wave rectifier. The complete model gave a good approximation to the system output when subjected to the same input signal.