Abstract

Relative to body size, the cerebellum of members of the dolphin family is the largest among Cetacea and possibly among all mammals. In the human brain about half of all neurons are in the cerebellum. Neuron density in the dolphin cerebellum is second only to that of humans, and because the dolphin cerebellum is 50% larger than that of humans relative to brain mass, the total number of neurons in the dolphin cerebellum is around 40% larger than in humans.

Experiments relative to function of the cerebellum are quite difficult and often very invasive. What has been learned about cerebellar function has been derived from damaging disease or injury to humans or invasive experiments in laboratory animals. Relatively non-invasive methods have now been developed for study of the dolphin cerebellum. For the first time, we have employed functional imaging by magnetic resonance imaging (MRI), positron emission tomography (PET) and single photon emission tomography (SPECT) to study metabolism and blood flow in the living dolphin. MRI was used to provide anatomical detail for registering PET and SPECT scans. In keeping with a high cell density, the dolphin cerebellum is metabolically active and shows a relatively high blood flow.