The Effect Of Stimulus Duration On IC Function Of Dealing Doppler Shift Compensation In Hipposideros Armiger

Echolocation is an essential ability for bats,which is necessary for environmental detection and preying.To complete echolocation task better,CF-FM(constant frequency-frequency modulation)bat have evolved some special abilities,among which the most representative is doppler shift compensation(DSC).Bats can adjust their vocal frequency to maintain echo frequency within the most sensitive range,which can reduce the influence of doppler shift effect.Behavioral studies have shown that the frequency of compensation will change with flight phases.Bats accelerate their fight speed in search phase,and speed reaches a peak in approach phase,then decrease in terminal phase until finish the preying.In such process,many other sound parameters,include echo delay,sound amplitude,duration and pulse repetition etc.,change with the frequency of compensation.Current electrophysiological studies have shown a covariant relationship among these sound parameters,which will affect neural response.But how the change of these parameters influence DSC still remains unknown.Since the sound duration,which constantly decreases when bat is approaching to the target,can be used as the labor of flight phase changing.We simulate the duration changing in the fight of Hipposideros armiger to explore how duration changing influence the analysis of DSC signal in the IC neurons of Hipposideros armiger,and the obtained results are summarized as following:(1)97 auditory neurons were found in this study,among which 48 neurons(49.5%)were duration selective and 49 neurons(50.5%)were non-duration selective.We found that the frequency of best compensation of duration selective and non-duration selective neurons were significantly different(p<0.05).The frequency of best compensation of duration selective neurons centralized in 1-2 kHz,and non-duration selective neurons centralized beyond 2 kHz,which is far beyond the frequency of compensation recorded in behavioral study.This suggest a division of labor among duration selective neurons and non-duration selective neurons,otherwise,the non-duration selective neurons may not participate in DSC coding.(2)The result of One-way ANOVAs showed that the frequency of best compensation in duration selective neurons change significantly with the variation of duration(p<0.05),and there is no significant differences in non-duration selective neurons.What’s more,the frequency of best compensation under 7 ms was higher than other flight phase in duration selective neurons,which was consistent to behavioral recording,This suggest that there is a covariant relationship between the frequency of best compensation and duration in duration selective neurons.(3)We found that the trend in frequency of compensation-50%IPI curve is different between duration selective and non-duration selective neurons.50%IPI of duration selective neurons was minimum when frequency of compensation is about 1 kHz.But in non-duration selective neurons 50%IPI decreased when the frequency of compensation was increased,which was similar to the result we found in Kuming mice and FM bats that never have DSC behavior.We assume that duration selective neuron may evolve a mechanism to decrease the influence of masking,which can maintain the sensitivity if neurons to handle DSC signal better.(4)In this study,we also found that nonlinear regression curve of best duration(BD)and the frequency of best compensation is y=(2.566*x)/(5.136+x),that was frequency of best compensation increased when the best duration increased,which was not consistent to behavioral recording.But the frequency of best compensation under different duration is consistent to behavioral recording,which suggest that frequency of best compensation is not the characteristic parameter,but mediated by other sound parameters,and one neuron can code multiple frequency of compensation.This mechanism could be the result of amplification in outer hair cell.In conclusion,duration selective and non-duration selective neurons may have division of labor.Variation in duration can affect the preference of duration selective neuron in frequency of compensation.And DSC may decrease the effect of masking to duration selective neurons.The DSC signal may be coded by single neuron rather than the cooperation of multi-neurons.Above results will contribute to the study in collaborative coding of duration and DSC signal.