Two-tone suppression and song coding by ascending neurones in the cricketGryllus campestris L.

Summary

• 1. A new type of ascending interneurone (AN3) responding to airborne sound has been characterised morphologically and physiologically in the prothoracic ganglion of the cricketGryllus campestris (Fig. 1).

• 2. The structure of AN3 is generally similar to that of two ascending neurons described previously (AN1, AN2).

• 3. AN3 is highly tuned and very sensitive (threshold at CF, 30–35 dB SPL; Q₁₀=3) to the calling song frequency. The tuning is enhanced by inhibitory sidebands on both the low and high frequency side (tuned to 3 kHz and 16 kHz respectively; Fig. 1).

• 4. The other two AN types also show two-tone suppression effects which generally act so as to enhance the contrast of the response to the best frequency (Fig. 3–5). In contrast to AN3 and AN1, AN2 shows a great variability in its responses to low frequency sounds.

• 5. AN3 and AN1 respond preferentially to the conspecific calling and aggression songs, supplementing each other in the intensity domain. AN2 responds only unspecifically to the calling and aggression songs but strongly to courtship syllables (Fig. 6).

• 6. Stimulation with artificial song models reveals that the song specificity of AN3 and AN2 is due mainly to the frequency content of the songs. In AN2, an additional influence from the temporal structure becomes apparent (Fig. 6).