Birds have primate-like numbers of neurons in the forebrain.
Some birds achieve primate-like levels of cognition, even though their brains tend to be much smaller in absolute size. This poses a fundamental problem in comparative and computational neuroscience, because small brains are expected to have a lower information-processing capacity. Using the isotropic fractionator to determine numbers of neurons in specific brain regions, here we show that the brains of parrots and songbirds contain on average twice as many neurons as primate brains of the same mass, indicating that avian brains have higher neuron packing densities than mammalian brains. Additionally, corvids and parrots have much higher proportions of brain neurons located in the pallial telencephalon compared with primates or other mammals and birds. Thus, large-brained parrots and corvids have forebrain neuron counts equal to or greater than primates with much larger brains. We suggest that the large numbers of neurons concentrated in high densities in the telencephalon substantially contribute to the neural basis of avian intelligence.
Department of Zoology, Faculty of Science, Charles University in Prague, CZ-12844 Prague, Czech Republic;
Seweryn
S
Olkowicz
Department of Zoology, Faculty of Science, Charles University in Prague, CZ-12844 Prague, Czech Republic;
Martin
M
Kocourek
Department of Zoology, Faculty of Science, Charles University in Prague, CZ-12844 Prague, Czech Republic;
Radek K
RK
Lučan
Department of Zoology, Faculty of Science, Charles University in Prague, CZ-12844 Prague, Czech Republic;
Michal
M
Porteš
Department of Cognitive Biology, University of Vienna, 1090 Vienna, Austria;
W Tecumseh
WT
Fitch
Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, CEP 21941-902, Rio de Janeiro, Brazil; Instituto Nacional de Neurociência Translacional, Ministério da Ciência e Tecnologia/Conselho Nacional de Pesquisas, CEP 04023-900, São Paulo, Brazil.
Suzana
S
Herculano-Houzel
Department of Zoology, Faculty of Science, Charles University in Prague, CZ-12844 Prague, Czech Republic; pgnemec@natur.cuni.cz.
Pavel
P
Němec
D000818:Animals; D001717:Birds; D001921:Brain / Q000166:cytology*; D002452:Cell Count; D005260:Female; D008297:Male; D009474:Neurons; D011323:Primates
birds; brain size; evolution; intelligence; number of neurons