Non-monotonic response-intensity characteristics of auditory receptor cells inLocusta migratoria

Abstract

1. Acoustic receptor cells of locusts adapt to long lasting stimulus trains. This temporal adaptation depends on the stimulus repetition rate (Fig. 1a) as well as on the sound pressure level (Fig. 1c). Beyond ca. 5 s train a ‘steady state’ is reached. 2. All receptor neurons show non-monotonic response characteristics if sound stimuli of modulation frequencies (sinusoidal modulation) or repetition rates (pulse-shaped modulation) higher than 5 Hz are applied (Fig. 2). Thus, the response (i.e. spikes/stimulus period) depends on both the sound pressure level L and the repetition rate f. The response characteristics form one response maximum, which shifts to lower L with increasing repetition rates. 3. The response latenciesΔt, however, decrease monotonically with increasing sound pressure levels for all applied repetition rates f (Fig. 3 a) and, thus, do not correlate linearily to the spike response as they do in the ‘static case’ (f≦2Hz) (Fig. 3b). In addition, the latency rises with higher f (Fig. 3a). 4. The consequences of these findings for previous investigations on the nervous system of locusts are discussed. The importance of both intensity coding and the stimulus repetition rate of receptor neurons for sound pattern processing is shown.