The elephant brain in numbers

Herculano‐Houzel, Suzana; Avelino-de-Souza, Kamilla; Neves, Kleber; Porfírio, Jairo; Messeder, Débora; Feijó, Larissa Mattos; Maldonado, J.; Manger, Paul R.

doi:10.3389/fnana.2014.00046

Cited by 113 publications

(106 citation statements)

References 57 publications

(107 reference statements)

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“…Humans, by contrast, have three times more neurons in the cerebral cortex than the African elephant [22], but require a much larger 8-9 h of sleep daily [7]. I propose that the reason why humans and other primates as a whole require many more hours of sleep for a similar number of cortical neurons than non-primates is that because of the way the primate cortex evolved to be built, this number of neurons is accompanied by a larger D/A in primates than in non-primates.…”

Section: (D) Implications For Mammalian Evolutionmentioning

confidence: 99%

“…Here I examine this second prediction that total sleep duration decreases together with neuronal density mm 22 across mammalian species and in their development. To this end, I present an analysis of a set of 24 species belonging to six mammalian clades for which cortical numbers of neurons, neuronal density and surface area were available [18][19][20][21][22][23][24][25][26][27][28][29], as well as data for total number of sleep hours per day [7]. Data are provided in table 1.…”

Section: Introductionmentioning

confidence: 99%

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Decreasing sleep requirement with increasing numbers of neurons as a driver for bigger brains and bodies in mammalian evolution

Herculano‐Houzel

2015

Proc. R. Soc. B.

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Mammals sleep between 3 and 20 h d 21 , but what regulates daily sleep requirement is unknown. While mammalian evolution has been characterized by a tendency towards larger bodies and brains, sustaining larger bodies and brains requires increasing hours of feeding per day, which is incompatible with a large sleep requirement. Mammalian evolution, therefore, must involve mechanisms that tie increasing body and brain size to decreasing sleep requirements. Here I show that daily sleep requirement decreases across mammalian species and in rat postnatal development with a decreasing ratio between cortical neuronal density and surface area, which presumably causes sleepinducing metabolites to accumulate more slowly in the parenchyma. Because addition of neurons to the non-primate cortex in mammalian evolution decreases this ratio, I propose that increasing numbers of cortical neurons led to decreased sleep requirement in evolution that allowed for more hours of feeding and increased body mass, which would then facilitate further increases in numbers of brain neurons through a larger caloric intake per hour. Coupling of increasing numbers of neurons to decreasing sleep requirement and increasing hours of feeding thus may have not only allowed but also driven the trend of increasing brain and body mass in mammalian evolution.

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Section: (D) Implications For Mammalian Evolutionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Decreasing sleep requirement with increasing numbers of neurons as a driver for bigger brains and bodies in mammalian evolution

Herculano‐Houzel

2015

Proc. R. Soc. B.

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“…The largest number of cortical neurons in non-primate mammals is found in the false killer whale with 10 500 million and the African elephant with 11 000 million, which is less than the number found in humans, despite the much larger brains of the former two. Herculano-Houzel et al [35] reported a much lower number of 5600 million neurons in the African elephant, which is about one-third of the number of neurons found in the human cerebral cortex. The reason for this is that the cortices of whales and elephants, despite their very large surface area, are much thinner, their cortical neurons are much larger and accordingly their NPDs are much lower.…”

Section: The Cortex As a Dominant Contributor To The 'Seat' Of Intellmentioning

confidence: 99%

Neuronal factors determining high intelligence

Dicke¹,

Roth²

2016

Phil. Trans. R. Soc. B

131

107

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One contribution of 16 to a discussion meeting issue 'Homology and convergence in nervous system evolution'. Many attempts have been made to correlate degrees of both animal and human intelligence with brain properties. With respect to mammals, a much-discussed trait concerns absolute and relative brain size, either uncorrected or corrected for body size. However, the correlation of both with degrees of intelligence yields large inconsistencies, because although they are regarded as the most intelligent mammals, monkeys and apes, including humans, have neither the absolutely nor the relatively largest brains. The best fit between brain traits and degrees of intelligence among mammals is reached by a combination of the number of cortical neurons, neuron packing density, interneuronal distance and axonal conduction velocity-factors that determine general information processing capacity (IPC), as reflected by general intelligence. The highest IPC is found in humans, followed by the great apes, Old World and New World monkeys. The IPC of cetaceans and elephants is much lower because of a thin cortex, low neuron packing density and low axonal conduction velocity. By contrast, corvid and psittacid birds have very small and densely packed pallial neurons and relatively many neurons, which, despite very small brain volumes, might explain their high intelligence. The evolution of a syntactical and grammatical language in humans most probably has served as an additional intelligence amplifier, which may have happened in songbirds and psittacids in a convergent manner.

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“…For instance, the largest land mammal, the elephant, has a cerebral cortex that weighs twice as much as the human cortex. However, because the brains of different animals are built in different ways, the elephant's gigantic cortex has only a third of the neurons that humans have in their cerebral cortex [3,4]. The lesson here is that size may be important, but it is far from everything when it comes to comparing brains.…”

Section: Carnivoresmentioning

confidence: 98%