No abstract

SUMMARY  Unihemispheric and bihemispheric sleep deprivation were performed in bottlenose dolphins. One brain hemisphere was capable of being deprived of delta (0.5‐3.0 Hz) sleep in the former condition. Here, an increase in sleep pressure was observed during sleep deprivation in the deprived hemisphere. In the recovery sleep, following unihemispheric sleep deprivation, there was a rebound of delta sleep only in the deprived hemisphere. Following bihemispheric sleep deprivation the animals exhibited an increase in delta sleep in both hemispheres.

No abstract

Temporary threshold shifts can be short-lived in the bottlenosed dolphin and therefore difficult to measure with conventional trained behavioral psychophysical techniques. The time course of recovery from temporary threshold shifts was measured using evoked auditory potentials collected from a bottlenosed dolphin trained to wear rubber suction cups containing human EEG skin surface electrodes. During each session, following an initial measure of hearing thresholds using the evoked auditory potential procedure, the animal voluntarily positioned within a hoop 1 m underwater while 160 dB re 1 micropascal noise between 4 and 11 kHz was presented for 30 min. Immediately following the noise exposure, evoked thresholds were again obtained. The dolphin swam down into a second hoop located one meter in front of a calibrated hydrophone. Evoked potential thresholds were obtained 5, 10, 15, 25, 45, and 105 min following the exposure for amplitude modulated pure tones of 8, 11.2, 16, 22.5, and 32 kHz. Maximum shifts occurred 5 min following exposure and rapidly recovered. As has been observed with other animals and humans, threshold shifts depended on frequency. Shifts occurred at 8, 11.2, and 16 kHz but no shifts were detected at 22.5 and 32 kHz.