Frequency Selectivity For CF Component Of Behavior-related Sound Signal In Inferior Collicular Neurons Of Hipposideros Pratti

The echolocation sound of constant frequency-frequency modulated (CF-FM) consisted of CF component and FM component, which played different roles during bat’s echolocation. However, CF component and FM component could also affect each other. Our previous studies found the inferior collicular (IC) neurons could be classified into single-on (SO) and double-on (DO) neurons under CF-FM stimuli. However, whether there were any differences in the frequency selectivities between them are still unclear. Under free field stimulation condition, we studied the auditory response properties of IC neurons of 15 Hipposideros pratti [seven males, eight females,40.5～56.0 (46.3±3.6) g body weight] used extracellular recording in vivo. Results are as follows:1. The proportion of multipeak (MP) frequency spikes curves (FSCs) in DO neurons (20.9%) was more than that of SO neurons (2.3%) under CF sound stimuli. While under CF-FM sound stimuli, the proportion of lower-tail-upper-sharp (TL) FSCs decreased (31.8% to 9.1%) in SO neurons, but there were no significantly differences in DO neurons. There were no significantly differences in 75% Bandwidths (BWs) of FSCs between SO neurons and DO neurons under CF stimulation condition (p>0.05). Under CF-FM sound stimuli, BWs of 43.2% SO neurons decreased, while BWs of 50% DO neurons increased. Therefore, BWs of SO neurons were significantly lower than that of DO neurons (p<0.01) under CF-FM stimulation condition. These results indicated that the FM component could affect the frequency selectivity of CF component in the IC neurons of Hipposideros pratti, and the SO neurons had higher frequency selectivities than DO neurons, suggesting that SO and DO neurons played different roles during echolocation.2. Compare the BWs of FSCs under CF-FM sound stimuli of three phases duration in SO and DO neurons. The results showed the BWs decreased with the increasing of sound duration in SO neurons, but the BWs were unaffected by sound duration in DO neurons. And the BWs of DO neurons were always significantly higher than SO neurons (p<0.01) in all duration we tested. These results suggested the SO neurons had higher frequency selectivities than DO neurons in any phases, and the frequency selectivities were higher during searching phase than the other phases in SO neurons. These results prompted that SO neurons might be used to analysis the fine frequency change resulted from Doppler frequency shift, and DO neurons might be used to analysis the information of insects’flapping.