Recovery Cycle of Inferior Collicular Neurons Determine Pulse Following Rate in CF-FM Bat*

Abstract

The characteristics of recovery cycles in inferior collicular (IC) neurons of leaf-nosed bat (Hipposideros armiger) and effect of the recovery cycle on the following pulse repetition rate were studied using mimic CF-FM sound stimuli emitted by free flying bat. Recovery cycle of 93 IC neurons were obtained from IC of five bats with normal hearing. These neurons were classified into three types, i.e. long recovery (LR, 47.4%), moderate recovery (MR, 35.1%), and short recovery (SR, 17.5%), according to their inter pulse interval (IPI) (ms) of 50% recovery under two CF-FM sound stimulation condition. Each type of the neurons could also be categorized into different sub-types according to changes induced by IPI increasing such as single-IPI response area neurons, multi-IPI response area neurons, and monotonic-IPI response neurons. Mean IPIs of 50% recovery of LR, MR, and SR neurons were (64.0 ± 24.8), (19.6 ± 5.8), and (7.1 ± 2.4) ms, respectively (P 0.001). The calculated theoretically following pulse repetition rate (pulse per second, Hz) of LR, MR, and SR neurons by mean IPI of 50% recovery for each type were (18.2 ± 7.0), (55.4 ± 15.7), and (171.3 ± 102.9) Hz, respectively (P 0.001). These three types of IC neurons were well corresponding to their three hunting phases, search, approach, and catch phases. The sub-types of single-IPI response area neurons and multi-IPI response area neurons had hunting phase selectivity, and sub-type of monotonic-IPI response neurons had well sensitivity to IPI change, but their hunting phase selectivity was of a sort. These results demonstrated that recovery cycle of IC neurons determined the ability to follow pulse repetition rate and matched this bat's echolocation behavior.