An investigation of dolphin neocortex using computed tomography and magnetic resonance Imaging

Abstract

The value of the conventional medical imaging applications of Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) to areas such as medical diagnosis and surgical planning are widely documented; however, less conventional uses also exist for such technology. This paper documents an example of the diverse, interdiscipl inary value of neuroradiological techniques such as CT and MRI. An assumption has been made, in the absence of data for dolphins, that the uniquely high relative neocortex volume in primates is responsible for setting them apart from all other orders of mammals, in terms of social intelligence. An investigation of dolphin brain structure was undertaken to verify or dismiss this assertion using three species ofdiffering social structure: sol itary humpback (Sousachinensis), social bottlenose (Tursiops truncatus) and gregarious common (Delphinus delphis) dolphins. CT provided good quality images for calculation of cranial volume but only permitted gross imaging of the supra- and infratentorial regions. MRI provided greater differentiation of the different brain regions, therebya"owing volumetric measurements of the neocortical region for all subjects. There was no significant difference in neocortex calculations from fresh and frozen material, suggesting that this technique may be used on rare specimens which are frozen before examination by biologists. Correlation of neocortical development with group size was significant (pO.OOl ).