Neurons in the inferior colliculus, auditory cortex and pontine nuclei of the FM bat, Eptesicus fucus respond to pulse repetition rate differently.

Single-neuron responses to pulse repetition rate in the inferior colliculus, auditory cortex and pontine nuclei of the FM bat, Eptesicus fuscus were studied under free-field stimulation conditions. The best frequency (BF) and minimum threshold (MT) of each neuron were first determined with a 4 ms pulse broadcast from a specific point (response center) of the bat's frontal auditory space at which the neuron had maximal spatial sensitivity. The neuron's intensity-rate function was then studied with a 4 ms BF pulse delivered at 10 dB increments above its MT in order to determine the best intensity to which the neuron discharged maximally. The neuron's discharge pattern and number of impulses to 32 trials of 300 ms train stimuli, which consisted of different number of 4 ms BF and best intensity pulses (1, 2, 3, 8, 12, 19, 24, 29 pulses/train) and delivered at an interpulse interval of 1000, 250, 170, 100, 40, 25, 15, 12 and 10 ms (i.e. at a pulse repetition rate of 1, 4, 6, 10, 25, 40, 67, 83, 100 pulses/s), were sequentially recorded. All neurons recorded from the inferior colliculus, auditory cortex and pontine nuclei discharged phasically (1-3 impulses) but they responded to the pulse repetition rate in different manners. More than 63% of 38 inferior collicular and 65 pontine neurons studied discharged impulses to each pulse within a train stimulus when the pulse repetition rate was up to 40 pulses/s.(ABSTRACT TRUNCATED AT 250 WORDS)