Imaging acoustic centers of the dolphin brain with positron emission tomography

Abstract

In human subjects, positron emission tomography (PET) has been used in diagnosis of disease, in studies of complex cognitive tasks, and in localizing areas of sensory activation, motor movement, and attention. Now, brain physiology of bottlenose dolphins, Tursiops truncatus, has been studied with PET. The dolphin brain is in the human size range but is more highly convoluted. The known acoustic centers of the dolphin brain are greatly enlarged compared with human brains. However, dolphins have a multi-tiered cortex with an extensive extra lobe, the paralimbic lobe, which does not occur in mammals or other animals outside the Order Cetacea. Because of its inaccessible location, there are no functional studies of the paralimbic cortex. PET offers an opportunity to study activity in this unique part of the dolphin brain during various stimulus conditions that may help to reveal functional aspects of the paralimbic cortex. For experimental scans, the dolphin was exposed to acoustic stimuli (tones or pulses) to reveal areas of relative brain metabolism after 18-F-FDG administration. These scans have revealed interesting features of the living dolphin brain including the paralimbic lobe as well as known acoustic areas in the cortex, midbrain, and acoustic nuclei.