Brain

Bowhead whales are one of the least encephalized mammals, possessing a small brain relative to their body size (e.g., a 3kg brain in a 30,000kg body). Features of the bowhead whale brain include a blunted temporal lobe and a gyrification index that is less than most cetaceans. Rather than having a cerebrum that is wider than long like odontocetes, the bowhead cerebrum is longer than it is wide. The hippocampus is very small and located within the lateral ventricle, which is ventral to the corpus callosum. The cytoarchitecture of the bowhead cerebral cortex is consistent with that of other cetaceans. The cortex is thin overall with a relatively thick, prominent layer I. As with other cetaceans, there is no granular layer IV. Notably, high numbers of von Economo neurons and fork neurons are found in all regions of the cortex. The highest numbers of these special neurons are observed at the apex of gyri.