Auditory brainstem response recovery from forward masking in insectivorous and frugivorous bats

Echolocating bats rely on precise temporal processing of sound, as echolocation calls may be emitted at rates as high as 150–200 sounds per second in the terminal “buzz” phase that precedes prey capture by insectivorous species. High call repetition rates could introduce forward masking effects that interfere with echo detection; however, echolocating bats may have evolved auditory specializations to prevent repetition suppression of auditory responses and facilitate detection of sounds separated by very brief time intervals. We assessed the time course of post-stimulus recovery of the auditory brainstem response (ABR) in two bat species that differ in the temporal characteristics of their sonar behaviors: the insectivorous Eptesicus fuscus, which uses high sonar call rates to capture prey and the frugivorous Carollia perspicillata, which uses lower call rates to forage. We recorded forward-masking ABRs to paired clicks at varied inter-stimulus intervals and measured recovery from prior stimulation as the ratio of response amplitudes and latencies evoked by the second stimulus relative to the first. We observed significant species-specific effects of forward masking on ABR responses in which E. fuscus maintained comparable responses to ISIs less than 4 ms compared to longer post-stimulus response recovery times (>6 ms) in C. perspicillata.