Evoked potential study of the inferior collicular response to constant frequency-frequency modulation (CF-FM) sounds in FM and CF-FM bats.

The auditory system of echolocating bats is adapted for processing species-specific ultrasonic signals. While FM (frequency modulation) bats are strictly sensitive to the frequency ranges of their orientation signals or prey-generated noise, CF-FM (constant frequency-FM) bats have a disproportionate number of neurons tuned to frequencies near the CF component of their orientation sounds, and most of them are on-off responders. Furthermore, the inferior collicular neurons of the CF-FM bats discharged as single-on or double-on responders to CF-FM stimuli. To further study the differences in auditory signal processing of these two types of bats, as the first step we conducted an evoked potential response study in the inferior colliculus of the CF-FM bat, Hipposideros pratti and the FM bat, Pipistrellus abramus using CF, FM and CF-FM stimuli. The results showed that the CF sounds always evoked collicular on- and off-responses in CF-FM bats, but the FM bats only had on-responses to both CF and FM sounds, indicting species-specific neural circuits. However, when stimulated with CF-FM sounds, collicular responses were evoked by both the CF and FM components from both FM and CF-FM bats, suggesting they have some generic neural circuit.

Recovery cycle of inferior collicular neurons in Hipposideros pratti under behavior-related sound stimulus and the best Doppler-shift compensation conditions.

The Doppler-shift compensation (DSC) behavior of constant frequency - frequency modulation (CF-FM) bat (Hipposideros pratti) is vital for extraction and analysis of echo information. This type of behavior affects the recovery cycles of sound-sensitive neurons, but their precise relationship remains unclear. In this study, we investigated the effects of DSC on the recovery cycles of inferior collicular (IC) neurons in H. pratti. We simulated the pulse-echo pair in bats by changing the emitted pulse frequency and keeping the echo frequency constant during DSC in echolocation. The neuronal recovery cycles of IC neurons are categorized into four types: unrecovered, monotonic, single-peak, and multi-peak. The recovery cycle of IC neurons shortens after DSC; moreover, the amount of neurons with multi-peak recovery cycle increases and concentrates in the short recovery area. This paper also discusses the possible neural mechanisms and their biological relevance to different phases of bat predation behavior.

Sexual dimorphism in echolocation pulse parameters of the CF-FM bat, Hipposideros pratti.

BACKGROUND: Previousstudies of sexual dimorphism in the echolocation pulses of the constant frequency-frequency modulating (CF-FM) bat have been mainly concentrated on the difference in the frequency of the CF component of the predominant second harmonic while neglected other pulse parameters. However, recent studies have shown that other pulse parameters of the predominant second harmonic are also biologically significant to the bat hunting. To complement and advance these studies, we have examined sexual dimorphism of multiple parameters (e.g., duration, frequency, bandwidth of the FM component, and repetition rate of emitted pulses) of the echolocation pulses of the CF-FM bat, Hipposideros pratti. RESULTS: Our studies of the predominant second harmonic show that on average the male bat has higher frequency of the CF component, wider FM bandwidth, and higher pulse repetition rate while the female bat has longer duration of the CF and FM components. CONCLUSIONS: Theseobservations suggest that bats may potentially use this sexual dimorphism in echolocation pulse parameters for social communication and species and sex identification.