title: The elephant brain in numbers.
abstract: What explains the superior cognitive abilities of the human brain compared to other, larger brains? Here we investigate the possibility that the human brain has a larger number of neurons than even larger brains by determining the cellular composition of the brain of the African elephant. We find that the African elephant brain, which is about three times larger than the human brain, contains 257 billion (10(9)) neurons, three times more than the average human brain; however, 97.5% of the neurons in the elephant brain (251 billion) are found in the cerebellum. This makes the elephant an outlier in regard to the number of cerebellar neurons compared to other mammals, which might be related to sensorimotor specializations. In contrast, the elephant cerebral cortex, which has twice the mass of the human cerebral cortex, holds only 5.6 billion neurons, about one third of the number of neurons found in the human cerebral cortex. This finding supports the hypothesis that the larger absolute number of neurons in the human cerebral cortex (but not in the whole brain) is correlated with the superior cognitive abilities of humans compared to elephants and other large-brained mammals.
authors: Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil ; Instituto Nacional de Neurociência Translacional São Paulo, Brazil.
authors: Suzana
authors: S
authors: Herculano-Houzel
authors: Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil ; Instituto Nacional de Neurociência Translacional São Paulo, Brazil.
authors: Kamilla
authors: K
authors: Avelino-de-Souza
authors: Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil ; Instituto Nacional de Neurociência Translacional São Paulo, Brazil.
authors: Kleber
authors: K
authors: Neves
authors: Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil ; Instituto Nacional de Neurociência Translacional São Paulo, Brazil.
authors: Jairo
authors: J
authors: Porfírio
authors: Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil ; Instituto Nacional de Neurociência Translacional São Paulo, Brazil.
authors: Débora
authors: D
authors: Messeder
authors: Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil ; Instituto Nacional de Neurociência Translacional São Paulo, Brazil.
authors: Larissa
authors: L
authors: Mattos Feijó
authors: MBF Bioscience, Inc. Rio de Janeiro, Brazil.
authors: José
authors: J
authors: Maldonado
authors: School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand Johannesburg, South Africa.
authors: Paul R
authors: PR
authors: Manger
keywords: brain size; cerebellum; cerebral cortex; elephant; glia/neuron ratio; neuronal density; numbers of neurons