| The inferior colliculus(IC)is an important relay station in the central auditory pathway of mammalian midbrain and a center of subcortical auditory information processing.In the previous study of our lab,we found that the neurons of inferior colliculus(IC)showed two response patterns of single-on(SO)and double-on(DO),when stimulated with CF-FM signal to constant frequency-frequency modulation(CF-FM)bat.CF-FM bats can obtain environmental information by using the CF and FM components of the CF-FM signal,such as the relative speed,distance and texture of the target et al,so the different response pattern of neurons to the CF-FM signal meant different function in the echolocation behavior.By studying the factors affected the response pattern of SO and DO would help us to further understand the bat's echolocation behavior even mammals' auditory behavior.In this experiment,we used free acoustic field stimulation and extracellular recording technique to explore the response difference of SO and DO neurons to different acoustic signals under CF signal masking and the difference of frequency tuning.The results were as follows:(1)A total of 216 IC neurons were recorded in the experiment,including 170(170/216,78.7%)SO neurons and 46(46/216,21.3%)DO neurons.All DO neurons responded to 2 ms FM signal,while only 65.9%(112/170)of SO neurons responded to FM signal.The latency of DO neuron responded to FM signal was significantly less than that of SO neurons(10.3±3.7 vs 12.3±4.6 ms,P<0.01),and the firing rate was significantly higher than that of SO neurons(72.0±39.3 vs 48.8±35.7,P<0.001).These results suggested that DO neurons had a stronger ability to deal with FM signal than SO neurons.(2)Under double-sound stimulation,the SO and DO neurons had different 50%Gap values(the Gap value which the impulses reache to the 50%of maximum value)when response to different probe sounds(CF or FM).When the probe was CF signal,there was no significant difference in 50%Gap values between SO and DO neurons(58.4±52.3 vs 34.4±41.3 ms,P>0.05);while the probe was FM signal,the 50%Gap value of SO neurons was significantly larger than DO neurons(83.6±56.8 vs 16.1±37.2 ms,P<0.001).This result suggested that the formation of SO and DO response patterns is related to the temporal integration of inhibition induced by CF components and the excitatory inputs induced by FM sound components.(3)Apply GABA-A receptor antagonist bicuculline(BIC)to recording neurons made the impulses to FM signal increased,and the 50%Gap value responded to FM probe shortened under masking effect of CF sounds.These result suggested that GABAergic inhibitory input regulated the ability of these two types neurons to detect FM signals.(4)The response of SO and DO neurons to FM sounds(different sweep frequency ranges)and frequency tuning(FT)were different.The response of SO neurons to FM sound can be shown in three types:type ?,All frequency band sensitive neurons(N=51,34.9%),type ?,Narrow frequency band sensitive neurons(N=44,30.2%),type ?,Non-sensitived neurons(N=51,34.9%),while DO neurons all showed to type ?(N=37,100%).There was no significant difference in bandwidth(BW)between type ? SO neurons and DO neurons(29.1±16.8 vs 19.9±13.5 kHz,P>0.05(BW10);31.8 ± 17.3 vs 31.6±15.3 kHz,P>0.05(B30));while the BW10(tyoe ?,5.2±3.2 vs 19.9± 13.5 kHz;type ?,4.1±3.6 vs 19.9±13.5 kHz)and the BW30(type ?,12.1 ± 9.7 vs 31.6 ±15.3 kHz;type ?,5.9 ± 5.6 vs 31.6±15.3 kHz)of type ? and type ? SO neurons were significantly smaller than DO neurons(P<0.001).These results suggested that DO neurons had a wider frequency tuning range than SO neurons,which can accept a lot of excitatory inputs,and therefore can react to FM signals with different sweep range,while SO neurons showed different reaction to FM signal due to the diversity of FTC,which suggested that the input of FM component may had a modulation effect on CF component.Our study showed that SO neurons were more suitable to analyze the frequency change of echo CF,due to its only responded to CF components of CF-FM signal.Bat can used SO neurons not only for Doppler shift(DS)compensation to adjust vocalization,but also for insect identification by comparing and detecting "glint" caused by the insect wing.While DO neurons responded to both CF and FM components of CF-FM signal,and the on response to FM component were also equivalent to the off response to CF component.Therefore,the time interval between the CF and FM component may be used to measure the duration of CF,to identify the echo of self-pulse and to regulate the subsequent vocal duration as reference information feedback;besides this,the FM components carryed the distance information and the details of the target,by analyzing the FM sound components can help bat to obtain the distance and details information of the target. |
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