PULSE REPETITION RATE INCREASES THE MINIMUM THRESHOLD AND LATENCY OF AUDITORY NEURONS

The effect of pulse repetition rate on auditory sensitivity of the big brown bat, Eptesicus fuscus, was studied by determining the minimum t hreshold, response latency and recovery cycle of inferior collicular n eurons at different repetition rates under free field stimulation cond itions. In general, collicular neurons shortened the response latency and increased the number of impulses monotonically or non-monotonicall y with stimulus intensity. They recovered at least 50% when the interp ulse interval was 10-57 ms. In addition, they increased the minimum th reshold, lengthened the response latency, and reduced the number of im pulses discharged to each pulse with increasing repetition rate. The i ncrease in minimum threshold with repetition rate is partly because th e neuron can not recover from previous stimulation when the interpulse interval is shortened. This increase reduces a neuron's response sens itivity and thus diminishes its number of impulses to each presented p ulse. This increase also reduces the effectiveness of a given stimulus intensity which contributes to the lengthening of the neuron's respon se latency. Data obtained from single neuron recordings are used to hi ghlight these observations. Implications of present findings regarding the bat's echolocation are also discussed.