[Frequency domain analysis of the dynamic properties of the encoder in the slowly adapting crayfish stretch receptor neuron].

The transfer properties of the slowly adapting stretch receptor neuron can be suitably described in the frequency domain. The measurements are carried out by means of sinusoidally varying intracellular currents. The frequency response at low stimulation frequencies has been calculated from responses to current steps. At very low input frequencies the amplitude-frequency characteristic in the Bode diagram is nearly parallel to the abscissa. With increasing stimulation frequency the gain becomes larger and has a maximum at 1--3 Hz (stimulation frequency/carrier frequency (f/fo approximately 0.2). The amplitude-frequency characteristic decreases then, at first slowly then more rapidly, and reaches in the range of carrier frequency (f/fo approximately 1) small values. The phase-frequency characteristic shows at low input frequencies a small positive magnitude of 8--10(0). With higher stimulation frequencies the phase angle decreases and reaches negative values. In the range of carrier frequency the phase shift runs to -180 degrees. The present findings demonstrate also that the transfer function of the encoder depends on the carrier frequency of the receptor neuron. Larger carrier frequencies cause a decrease of the gain but the peak remains. This maximum shifts with increasing fo in direction to higher stimulation frequencies. The elimination of the encoder adaptation by means of a suitable model results in the frequency response of the real encoder. The above statements hold for higher stimulation frequencies too, but the typical differential behaviour at low frequencies disappears.