Vol. 50 No. 5, 2011

Frequency-Modulation Component of the Mimic Echolocation Sound can Increase the Sensitivity of Inferior Collicular Neurons to Sound Amplitude in the Leaf-Nosed Bat, Hipposideros armiger

Zi-Ying Fu, Jia Tang, Yang Li, Hong Zeng, and Qi-Cai Chen*

College of Life Sciences and Hubei Key Lab of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan 430079, China

Zi-Ying Fu, Jia Tang, Yang Li, Hong Zeng, and Qi-Cai Chen (2011) A frequency modulation (FM) component widely exists in many bats’ echolocation calls and human speech sounds. In order to investigate the role of the FM component in sound communication, 6 leaf-nosed bats, Hipposideros armiger, were used in this experiment. In total, 113 inferior collicular (IC) neurons were obtained, and the responses of 61 neurons among these neurons to constant frequency (CF) and mimic CF-FM sounds and their rate-amplitude functions (RAFs) were studied. According to the responses of the neurons to CF and CF-FM sounds at different amplitudes, RAFs of these neurons were classified into 3 types, monotonic, saturated, and non-monotonic. When CF sounds were changed into CF-FM sounds, the best amplitudes of the neurons decreased from 93.0 ± 9.8 to 84.4 ± 11.3 dB SPL (p < 0.01), and the dynamic ranges decreased from 27.5 ± 9.4 to 22.5 ± 8.5 dB (p < 0.05), but the slopes of the RAFs increased from 3.1 ± 1.4 to 4.1 ± 1.7%/dB (p < 0.05). By further analyzing the influence of the FM component on the firing rate of the neurons, it was shown that the FM component elevated the firing rate of the neurons at < 30 dB above the minimum threshold (MT), while reducing the firing rate at > 30 dB above the MT (p < 0.001). The results indicate that the FM component of CF-FM sound can increase the sensitivity of IC neurons to sound amplitude.

Key words: FM component, Rate-amplitude function, Sound amplitude sensitivity, Inferior collicular neurons.

*Correspondence: Tel: 86-27-67867229. Fax: 86-27-67861936. E-mail:qcchen2003@yahoo.com.cn