title: Short-term enhancement and suppression of dolphin auditory evoked responses following echolocation click emission.
abstract: Biosonar gain control mechanisms in a bottlenose dolphin were investigated by measuring the auditory steady-state response (ASSR) to an external tone while the animal echolocated. The dolphin performed an echo change-detection task that utilized electronically synthesized echoes with echo delays corresponding to 25- and 50-m target range. During the task, amplitude modulated tones with carrier frequencies from 25 to 125 kHz were continuously presented and the instantaneous electroencephalogram stored for later analysis. ASSRs were extracted from the electroencephalogram by synchronously averaging time epochs temporally aligned with the onset of the external tone modulation cycle nearest to each of the dolphin's echolocation clicks. Results showed an overall suppression of the ASSR amplitude for tones with frequencies near the click center frequencies. A larger, temporary suppression of the ASSR amplitude was also measured at frequencies above 40-50 kHz, while a temporary enhancement was observed at lower frequencies. Temporal patterns for ASSR enhancement or suppression were frequency-, level-, and range-dependent, with recovery to pre-click values occurring within the two-way travel time. Suppressive effects fit the patterns expected from forward masking by the emitted biosonar pulse, while the specific mechanisms responsible for the frequency-dependent enhancement are unknown.
authors.affiliation: U.S. Navy Marine Mammal Program, Space and Naval Warfare Systems Center Pacific, Code 71510, 53560 Hull Street, San Diego, California 92152, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: Finneran
authors.affiliation: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106, USA.
authors.forename: Roxanne
authors.initials: R
authors.lastname: Echon
authors.affiliation: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Mulsow
authors.affiliation: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106, USA.
authors.forename: Dorian S
authors.initials: DS
authors.lastname: Houser
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D050681:Bottle-Nosed Dolphin / Q000502:physiology*; D004455:Echolocation; D004569:Electroencephalography; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D008297:Male