Several physiological and anatomical observations suggest a degree of dolphin brain hemispheric independence. Left and right hemispheres alternate SWS by some unknown mechanism. The findings also demonstrate the potential value of functional scans to explore other aspects of dolphin brain physiology as well as pathology.ĭolphins and related small whales in the delphinoid cetacean family have shown slow wave sleep (SWS) electroencephalograms (EEG) in one brain hemisphere while producing waking EEG in the other( Serafetinides et al., 1970 Mukhametov et al., 1977 Mukhametov, 1984 Mukhametov, 1987 Ridgway, 2002 Lyamin et al., 2001 Lyamin et al., 2004). The findings suggest that unihemispheric reduction in blood flow and glucose metabolism in the hemisphere showing USW are important features of unihemispheric sleep.įunctional scans may also help to elucidate the degree of hemispheric laterality of sensory and motor systems as well as in neurotransmitter or molecular mechanisms of unihemispheric sleep in delphinoid cetaceans.
Scans using PET revealed hemispheric differences in brain glucose consumption when scans with and without diazepam were compared. Scans using SPECT revealed unihemispheric blood flow reduction following diazepam doses greater than 0.55 mg kg -1 for these 180-200 kg animals. MRIs were used to register functional brain scans with single photon emission computed tomography (SPECT)and positron emission tomography (PET) in trained dolphins. Diazepam has been shown to induce unihemispheric slow waves (USW), therefore we used functional imaging of dolphins with and without diazepam to observe hemispheric differences in brain metabolism and blood flow. This report documents the first use of magnetic resonance images (MRIs) of living dolphins to register functional brain scans, allowing for the exploration of potential mechanisms of unihemispheric sleep.
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