Role of frequency band integration in sharpening frequency tunings of the inferior colliculus neurons in the big brown bat, Eptesicus fuscus

By means of a particular two-tone stimulation paradigm in combination of using a pair of electrodes for simultaneously recoring from two inferior colliculus (IC) neurons,the current in vivo study is undertaken to explore the role of frequency band integration (FBI) in sharpening of frequency tuning in the big brown bat, Eptesicus fuscus. Three major results are found: (1) The paired neurons cor- related to FBI are located not only within the same frequency filter bandwidth (FFB), but also across different FFBs. The relations of their frequency tuning curves (FTCs) are mainly of two types: the flank-overlapped and overlaid patterns. (2) Although the sharpness of FTCs between paired neurons is mutual, the sharpening efficiency of neurons located within the same FFB is higher than that of neurons across FFBs, and the FTCs of neurons with the best frequencies (BF) of 20 --30 kHz are most strongly sharpened. (3) The strength of FBI is weak near the BF but gradually increased with fre- quencies away from the BF of sound stimuli. This suggests that the dynamical FBI of the IC neurons located within and across the FFBs might be involved in the formation of func- tional FFB structures.