Non-auditory, electrophysiological potentials preceding biosonar click production in bottlenose dolphins

Abstract

The auditory brainstem response (ABR) to a dolphin’s own emitted biosonar click may be measured by averaging epochs of the instantaneous electroencephalogram (EEG) that are time-locked to the emitted click. In this study, waves in the averaged EEG preceding the biosonar click-evoked ABR were measured using surface electrodes placed on the head in six configurations while dolphins performed an echolocation task. Simultaneously, clicks were measured using contact hydrophones on the melon and a hydrophone in the farfield. The results revealed an electrophysiological potential (the pre-auditory wave, PAW) preceding the production of each biosonar click. The largest PAW amplitudes occurred with the non-inverting electrode just posterior of the blowhole and right of the midline — the apparent side of biosonar click generation. Although the source of the PAW is unknown, the temporal and spatial properties rule out an auditory origin. The PAW may be a myogenic potential associated with click production; however, ...