Whales and dolphins lose heat to their aquatic environment 90 times faster than terrestrial animals in air. 

Even a slight drop in brain temperature makes many neurons inactive, greatly reducing mental activity. In a recent study we demonstrate that whales and dolphins possess a specialized brain heat-producing system to combat this environmental pressure of heat loss. They have the internal chemistry that allows the brain to function as its own heating element. 

Proteins called uncoupling proteins (UCPs) are involved in this internal heat production by preventing efficient ATP production for normal neuronal functions and instead convert this energy as heat. Results of the study showed that 90% of the neurons in whale and dolphin brains contain UCPs, much more than closely related species (such as the river hippopotamus that only has 35% of UCP containing neurons). 

30 to 70% of glia cells of whales and dolphins contain UCPs, which is 30% denser than other related species. Furthermore,  nerve terminals that contain the neurotransmitter noradrenaline are about 30% denser in whale and dolphin brains when compared to closely related species. Noradrenaline is involved in processes that control the concentration and activity of UCPs. 

These findings show that cetaceans have an increased ability for thermogenesis due to higher expression of UCPs. These heat-regulation mechanisms may have contributed to the evolution of large brain size in whales and dolphins.