The interference of sound and movement stimuli in auditory interneurons ofLocusta migratoria L.

Summary

• 1. Auditory interneurons of the migratory locustLocusta migratoria were identified by intracellular recording and staining in the meso- and metathoracic ganglia. The response to (i) acoustic stimuli, (ii) movement of a hindleg and (iii) a combination of the two kinds of stimuli were analyzed.

• 2. During acoustic stimulation (10 ms, 70 dB, pure tones at 4 or 12 kHz) the interneurons discharge 1–4 AP per pulse, with a latency of 10–25 ms (Fig. 1A, F; Fig. 4A, E).

• 3. Sinusoidal rotation of a hindleg (frequency: 2.5–20 Hz, amplitude: 4 mm) elicits, in one group of interneurons, phase-coupled suprathreshold response (Fig. 1B, E) and in another group a subthreshold excitation (Fig. 4B).

• 4. When acoustic and movement stimuli are presented simultaneously, both groups of interneurons show a general reduction of the auditory response (Fig. 1G; Fig. 4F). In those interneurons with suprathreshold responses to sound and movement the responses to the two kinds of stimuli show phase-dependent, reciprocal, influences (Fig. 1I, K; Fig. 3B, D).

• 5. Interneurons with suprathreshold responses only to acoustic stimuli, fail to respond at certain phases of leg movement (Fig. 4I, J; Fig. 6B).

• 6. Two possible mechanisms for the suppression of movement-coupled activity in the latter interneurons are discussed: (i) a general elevation of threshold and (ii) an inhibition by fibers with movement-specific responses.