Echolocation calls evoke precise EFP in bat IC.

(A, B) Two example neural recordings from a bat (R63) illustrating peaks (red dots) identified from the wideband signal (black), MUA (orange), and EFP (blue) by an adaptive threshold (gray dashed line). Both EFP and MUA were derived from the same wideband neural recording with different cutoff frequencies for the digital filters. The right column shows the spectrogram of the stimulus, the “standard” call (top), and the response latencies of the first peaks. The “standard” call was 3 ms in duration, 70-dB SPL in amplitude, and consisted of two quadratic harmonics with the first harmonic sweeping down from 55 kHz to 25 kHz. (C) Similar response latencies of EFPs were observed when the bat (R14) was either listening to simulated echolocation calls from a loudspeaker or spontaneously vocalizing bats. (D) Response latencies of EFPs were selective for stimulus parameters. Number n indicates the total number of EFP peaks detected over 20 trials, i.e., 20 repetitions of the same acoustic stimulus (gray inset). All stimuli were 3 ms in duration. The first harmonic swept down from 55 kHz to 25 kHz and the second harmonic from 110 kHz to 50 kHz. The white noise was from 110 kHz to 25 kHz. Response latency is not shown for the lower panels of (D) due to the very few responses. Data shown here were from a single bat (R63) and data from all three bats were shown in S1 Fig and S1 Data. All response latency data are presented as mean ± SD. EFP, extracellular field potential; IC, inferior colliculus; MUA, multiunit activity; SPL, sound pressure level.