Study On The Behavior-relativity And Species-specificity Of The Mode Of The CF-FM Sound Signal Processing In Bats And Mice

Our previous studies demonstrated that the auditory midbrain, inferior colliculus (IC) neurons of Hipposideros armiger, showed two discharging or response patterns of single-on (SO) and double-on (DO) under constant frequency-frequency modulation (CF-FM) sound stimulus condition. But it’s not clear the role of FM component in these two response patterns, so we study the effect of the FM component on the responses (the number of impulses) and response latency to the CF component with in vivo extracellular recording. In addition, it still is unknown whether these two discharge patterns is the species-specific for the CF-FM bat, or commonly exists in the mammals. By using auditory evoked potential combined with the computer averaging technique, we comparatively studied the responses of the ICs of echolocation bats, including Hipposideros pratti (a CF-FM bat) and Pipistrellus abramus (a FM bat), and non-echolocation animal, Mus musculus mice (Km), to CF, FM and CF-FM stimuli. The results were obtained in present study as following.1. Total 116 SO neurons and 37 DO neurons were isolated from inferior colliculus of Hipposideros armiger with extracellular recording. By comparing the discharge numbers and response latencies of the SO and DO neurons under CF and CF-FM simulation conditions, we found that the FM component could decrease the number of impulses elicited by CF in the SO and DO neurons and shorten the response latency to CF in the DO neurons.2. By comparative study with auditory evoked potential recoding in ICs of three animal species, the significant results were obtained. The IC of Hipposideros pratti generated the on-off response with 2～7 waves to CF stimulus, and off response of on-off affected by the recording depth, the duration, amplitude and frequency of CF; just generated the on response with 2～4 waves to FM stimulus; and generated the DO response with the harmonic relativity of calls emitted by this bat to CF-FM stimulus. In the Pipistrellus abramus, the IC generated the on response with 2～5 waves to CF and FM stimuli; but generated the DO response to CF-FM stimulus, responsed selectively to the duration or modulation rate of FM sound and expressed in the response amplitude and latency. However, the ICs of mice generated severally one on response with 2～4 waves to CF, FM and CF-FM stimuli. The results described in above text strongly indicated that these two types of the neurons possibly play different roles at different phases during hunting. Also these results imply that there exist the species-diversity and species-difference between the echolocating and non-echolocating mammals in the sound signal processing, and the formation of these response properties to different sound stimuli possibly have direct relativity with the evolution of auditory behavior.