The effect of sound intensity on duration-tuning characteristics of bat inferior collicular neurons

Previous studies have shown that inferior collicular neurons of the big bro wn bat, Eptesicus fuscus, serve as short-, band-, long- and all-pass filter s for sound durations. Neurons with band-, short- and long-pass filtering c haracteristics discharged maximally to a specific sound duration or a range of sound durations. In contrast, neurons with all-pass filtering character istics do not have duration selectivity. To determine if duration-tuning ch aracteristics of collicular neurons were tolerant to changes in sound inten sity, we examined the duration-tuning characteristics of collicular neurons using a wide range of sound intensities. Duration-tuning characteristics e xamined included the type, bandwidth and slope of duration-tuning curves. S ound intensity delivered within 20 dB of minimum threshold did not affect d uration-tuning characteristics of all collicular neurons studied. Sound int ensities at still higher levels did not affect the tuning characteristics o f two-thirds of collicular neurons but decreased the duration selectivity a nd changed the duration-tuning curves of the remaining one-third of neurons from one type to another. However, these two groups of duration-tuning col licular neurons were not separately organized inside the inferior colliculu s. The biological relevance of these findings to bat echolocation is discus sed.