[Electric stimulation of a sensory nerve with 70-micrometer electrodes].

Using the device of an implant (Fig. 1) for direct stimulation of the eighth cranial nerve (Zwicker et al., 1986) measurements have been performed after implantation of one electrode in the nervus suralis of the first author. The results show that threshold of sensation is reached at voltage amplitudes of about 600 mV for sinusoidal stimuli almost frequency independent in the range between 100 Hz and 3 kHz (Fig. 2). The impedance of the electrode (Fig. 3) was found to be remarkably smaller compared with values measured by Zollner (1982) in Ringer's solution. No clear relation between threshold value or impedance and active electrode area could be detected. However, there was a clear dependence of the threshold voltage on the angle between the direction of puncture of the electrode and the direction of the nerve. Parallel puncturing resulted in a 13 dB less sensitive threshold in relation to perpendicular puncturing. The practical dynamic range between the threshold of sensation and the threshold of pain was found to be 10 to 12 dB.