[Sleep and wakefulness in Callorhinus ursinus]

Area of Science:

• Marine Mammal Biology
• Neuroscience
• Sleep Research

Background:

• Understanding sleep patterns in marine mammals is crucial for their conservation and welfare.
• Previous research on pinniped sleep has not extensively explored interhemispheric brain activity.
• Northern fur seals (Callorhinus ursinus) represent a unique model for studying marine mammal sleep.

Purpose of the Study:

• To investigate the sleep-wakefulness cycles of northern fur seals.
• To analyze the electrocorticogram (ECoG) for interhemispheric asymmetry during sleep.
• To compare sleep characteristics of northern fur seals with other pinnipeds and cetaceans.

Main Methods:

• Implantation of electrodes in three subadult male northern fur seals for continuous monitoring.
• Recording of electrocorticogram (ECoG), neck electromyogram (EMG), electrooculogram (EOG), and electrocardiogram (ECG).
• Analysis of sleep stages (active wakefulness, relaxed wakefulness, slow-wave sleep, paradoxical sleep) and sleep cycle duration.

Main Results:

• Northern fur seals spent approximately 32.0% in active wakefulness, 31.7% in relaxed wakefulness, 30.5% in slow-wave sleep, and 5.8% in paradoxical sleep.
• The average sleep cycle duration was 22.6 minutes.
• Pronounced interhemispheric asymmetry in ECoG slow waves was observed in all individuals, occupying 15.0% of recording time, a novel finding in pinnipeds.

Conclusions:

• Northern fur seals exhibit a distinct sleep architecture with significant interhemispheric ECoG asymmetry.
• This asymmetry distinguishes them from Caspian seals but shows similarity to dolphins.
• The findings highlight unique neurophysiological adaptations in northern fur seals' sleep.