We conducted psychophysical and neurophysiological experiments to test the hypothesis that big brown bats suffer less severe temporary threshold shifts after noise exposure than other small mammals that also hear high frequency sounds. Five big brown bats were trained in psychophysical detection experiments to obtain thresholds to FM sweeps spanning the frequency range of their echolocation calls. Bats were then exposed to 115 dB of broadband noise for one hour, and thresholds re-measured 20 min and 24 hour after exposure. For all bats, threshold elevations at 20 min post-exposure were 3 dB or less, while at 24 hour post-exposure, thresholds were similar to those obtained pre-exposure. Local field potentials were recorded in the cochlear nucleus of anesthetized big brown bats before and after noise exposure. Neural thresholds to FM sweeps and to single tone frequencies were unaffected by noise exposure. These data suggest that big brown bats are an excellent model system to study naturally occurring immunity to noise damage. [Work supported by ONR and the Capita Foundation.]
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