Effect of echolocation behavior-related constant frequency–frequency modulation sound on the frequency tuning of inferior collicular neurons in Hipposideros armiger
In constant frequency–frequency modulation (CF–FM) bats, the CF–FM echolocation signals include both CF and FM components, yet the role of such complex acoustic signals in frequency resolution by bats remains unknown. Using CF and CF–FM echolocation signals as acoustic stimuli, the responses of inferior collicular (IC) neurons of Hipposideros armiger were obtained by extracellular recordings. We tested the effect of preceding CF or CF–FM sounds on the shape of the frequency tuning curves (FTCs) of IC neurons. Results showed that both CF–FM and CF sounds reduced the number of FTCs with tailed lower-frequency-side of IC neurons. However, more IC neurons experienced such conversion after adding CF–FM sound compared with CF sound. We also found that the Q20 value of the FTC of IC neurons experienced the largest increase with the addition of CF–FM sound. Moreover, only CF–FM sound could cause an increase in the slope of the neurons’ FTCs, and such increase occurred mainly in the lower-frequency edge. These results suggested that CF–FM sound could increase the accuracy of frequency analysis of echo and cut-off low-frequency elements from the habitat of bats more than CF sound.