Brain and cognition: cetacean encephalisation compared

The most complex brains in the animal kingdom

The sperm whale has the largest brain in the animal kingdom (~8.5 kg); the common bottlenose dolphin reaches the second highest encephalisation quotient (EQ) after humans. But size is not everything: the highly folded neocortex, the number of neurons (1.5 billion in humans, 5.8 billion in the common bottlenose dolphin) and the cellular organisation tell the story of an intelligence of another kind. This comparison tool puts the key figures in perspective.

Further reading

Cetacean intelligence is measured in several ways: see the cognitive tests (mirror, language), the catalogue of tools, the overview of cetacean intelligence and the senses (hearing, vision).

Encephalisation, neocortex and von Economo cells

The cetacean brain has one of the highest encephalisation quotients (EQ) in the animal kingdom after humans: ~5.3 in the common bottlenose dolphin, ~2.6 in the killer whale, against 1.0 for the “average mammal”. This increase falls mainly on the neocortex and in particular the parietal lobes, associated with sensory integration.

As early as 2006, the researchers Patrick Hof and Estel Van der Gucht identified von Economo cells (spindle neurons) in cetaceans, until then thought to be confined to the great apes and humans. These neurons are involved in social cognition, empathy and self-awareness, which sheds light on the success of cetaceans in the mirror test (Reiss & Marino, PNAS 2001) and on their capacity for vocal imitation documented in the beluga, the killer whale and the common bottlenose dolphin.