Comparative anatomical description of brain hemisphere surfaces in toninha dolphin and humans

Pontoporia blainvillei (cetacean order and odontoceti suborder), popularly known in Brazil as Toninha, is a small dolphin with a long, thin beak found on the southern shore waters of the western Atlantic. The brain development of dolphins (expressed by the encephalization coefficient) in relation to body size is quite high, and is second only to humans. This high correlation in brain development between dolphins and humans was targeted in this research to describe and compare the morphology of cerebral hemisphere surfaces of these two species. Five brains of Pontoporia blainvillei donated by the BioPesca Project (a non-governmental organization) were analyzed. The brains were fixed in 20% formaldehyde solution for further description and comparison to human brains described in books of neuroanatomy. The telencephalon of Pontoporia blainvillei is rostrally tapered and expanded at the caudal end and it has a greater number of folds/gyrus when compared to human species. Some encephalic grooves/sulcus are similar to grooves found in the human species, such as the cruciate sulcus (central sulcus), lateral fissure (Sylvian cleft), cingulate sulcus and calcarine sulcus. The same encephalic lobes are seen in both species; however the parietal and temporal lobes are highly developed in the Pontoporia blainvillei. These differences are associated with specific function of the species, as the presence of the an efficient auditive system in dolphins.