The Cetacean Brain

Cetaceans can be considered the pinnacle of evolution in terms of brain size, with the iconic sperm whale (Physeter macrocephalus) sporting the largest brain in known evolutionary history. In this chapter, we explore behind the scenes of cetaceans encephalization quotient, understanding how an ensemble of increasingly multidisciplinary, comparative, studies characterize the complexity of brain anatomy, cytoarchitecture, connectivity, and genetics in these aquatic specialists. While cetaceans are phylogenetically closer to hippopotamids, their brains are remarkably like those of humans and other large terrestrial animals, for example in being capable of complex social dynamics and prone to neurodegenerative disease, even though, they diverged significantly in terms of their diving adaptations and their neuroanatomy. Understanding neural adaptations in cetaceans can help us understand the nature of cognition and its malfunctions in large, long-lived homeotherms.