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First published online July 20, 2006
Journal of Experimental Biology 209, 2902-2910 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02348
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Functional imaging of dolphin brain metabolism and blood flow

Sam Ridgway1,2,*, Dorian Houser3, James Finneran1, Don Carder1, Mandy Keogh1, William Van Bonn1, Cynthia Smith1, Miriam Scadeng2, David Dubowitz2, Robert Mattrey2 and Carl Hoh2

1 SPAWAR Systems Center San Diego, Division 235, 53560 Hull Street, San Diego, CA 92152-5001, USA
2 School of Medicine, University of California, San Diego, CA 92093, USA
3 BIOMIMETICA, 7951 Shantung Drive, Santee, CA 92071, USA

* Author for correspondence at address 2 (e-mail: sridgway{at}UCSD.edu)

Accepted 25 May 2006

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. 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. MRIs were used to register functional brain scans with single photon emission computed tomography (SPECT) and positron emission tomography (PET) in trained dolphins. Scans using SPECT revealed unihemispheric blood flow reduction following diazepam doses greater than 0.55 mg kg-1 for these 180-200 kg animals. Scans using PET revealed hemispheric differences in brain glucose consumption when scans with and without diazepam were compared. The findings suggest that unihemispheric reduction in blood flow and glucose metabolism in the hemisphere showing USW are important features of unihemispheric sleep.

Functional 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. The findings also demonstrate the potential value of functional scans to explore other aspects of dolphin brain physiology as well as pathology.

Key words: dolphin, Tursiops, functional imaging, diazepam, SPECT scan, MRI scan, PET scan, brain, unihemispheric sleep, slow wave, hemisphere autonomy.


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