How many neurons
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AnimalHow many neurons?SDWhere?SourceMethod of counting
How many synapses?
Method of counting
Source, if different than neurons
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Nematoda
Nematode (Caenorhabditis elegans)
302Whole body
http://www.wormatlas.org/MoW_built0.92/MoW.html
Apparently sectioned and counted by hand under a microscope5000Also counted by hand?
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Ascarid lumbricoides2.54E+02Whole body
http://www.stri.si.edu/sites/publications/PDFs/2011_Eberhard_Wcislo_AdvIns_Physiol.pdf
Cited "Structure and Function in the Nervous Systems of Invertebrates", Bullock and Horridge, 1965. Apparently hand counted.
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MammaliaHuman (adult male)8.61E+108.10E+09Whole brain
http://onlinelibrary.wiley.com/doi/10.1002/cne.21974/abstract;jsessionid=FB6AC1F3B0F07CFA14087F187141E37E.f04t04
Whole-brain isotropic fractionation - apparatus that counts number of nuclei in a brain suspension, then determines the proportion of neuronal cells via immunocytochemical labelling of an antigen common to most neurons. http://www.sfn.org/~/media/SfN/Documents/Short%20Courses/2014%20SC%202/SC%202%20Chapters/Suzana%20HerculanoHouzel.ashx More details on this method.
1.6E+17
Estimated from a variety of data
http://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=4812&context=ujmm
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Rat2.10E+071.79E+05Cortex + cerebrum
https://www.ncbi.nlm.nih.gov/pubmed/2181205
Brain sectioned into thin random slices, stained with Gallocyanin-chromallum, a neuron stain, and counted.
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Rat1.89E+081.26E+07Whole brain
http://www.karger.com/Article/FullText/437413#T05
Whole-brain isotropic fractionation
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Rat5.52E+07Cortex
http://www.modha.org/C2S2/2009/11182009/content/SC09_TheCatIsOutofTheBag.pdf
(see cat neuron method)4.42E+11
(see cat neuron method)
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Cat7.63E+08Cortex
http://www.modha.org/C2S2/2009/11182009/content/SC09_TheCatIsOutofTheBag.pdf
From the source: "The total surface area of the two hemispheres of the rat cortex is roughly 6 cm^2 and that of the cat cortex is roughly 83 cm^2[29]. The number of neurons under 1mm^2 of the mouse cortex is roughly 9.2×10^4[34] and remains roughly the same in rat and cat [32]. Therefore, the rat cortex has 55.2×10^6 neurons and the cat cortex has 763×10^6 neurons. Taking the number of synapses per neuron to be 8,000[8], there are roughly 442×10^9 synapses in the rat cortex and 6.10×10^12 synapses in the cat cortex. The numbers for human are estimated in [22], and correspond to roughly 10,000 synapses per neuron.
6.10E+12
(see cat neuron method)
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African elephant (adult male)2.57E+11
http://journal.frontiersin.org/article/10.3389/fnana.2014.00046/full
Whole-brain isotropic fractionation (n=1)
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Smokey shrew (Sorex fumeus)3.65E+074.57E+06Whole brain
http://www.karger.com/Article/FullText/437413#T05
Whole-brain isotropic fractionation
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Mouse (Mus musculus)6.79E+071.04E+07Whole brain
http://www.karger.com/Article/FullText/437413#T05
Whole-brain isotropic fractionation
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Golden hamster (mesocricetus auratus)
8.42E+079.99E+06Whole brain
http://www.karger.com/Article/FullText/437413#T05
Whole-brain isotropic fractionation
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European rabbit (oryctolagus cuniculus)
4.94E+08Whole brain
http://www.karger.com/Article/FullText/437413#T05
Whole-brain isotropic fractionation (n=1)
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Domestic pig (Sus scrofa domesticus)
2.22E+09Whole brain
http://www.karger.com/Article/FullText/437413#T05
Whole-brain isotropic fractionation (n=1)
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Springbok (Antidorcas marsupialis)
2.72E+09Whole brain
http://www.karger.com/Article/FullText/437413#T05
Whole-brain isotropic fractionation (n=1)
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Rhesus macaque (Macaca mulatta)
6.38E+09Whole brain
http://www.karger.com/Article/FullText/437413#T05
Whole-brain isotropic fractionation (n=1)
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Orangutan (Pongo sp.)2.63E+102.47E+09Whole brain
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3064932/
Whole-brain isotropic fractionation (n=3)
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AvesRed junglefowl (gallus gallus)2.21E+084.45E+07Whole brain
http://www.pnas.org/content/113/26/7255/T1.expansion.html
Whole-brain isotropic fractionation, n of 3 birds
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Rock pigeon (Colombia livia)3.10E+083.33E+07Whole brain
http://www.pnas.org/content/113/26/7255/T1.expansion.html
Whole-brain isotropic fractionation, n of 3 birds
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Blackcap1.57E+081.89E+07Whole brain
http://www.pnas.org/content/113/26/7255/T1.expansion.html
Whole-brain isotropic fractionation, n of 3 birds
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Great tit2.26E+084.70E+07Whole brain
http://www.pnas.org/content/113/26/7255/T1.expansion.html
Whole-brain isotropic fractionation, n of 3 birds
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Starling4.83E+088.83E+07Whole brain
http://www.pnas.org/content/113/26/7255/T1.expansion.html
Whole-brain isotropic fractionation, n of 3 birds
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ReptiliaNile crocodile8.05E+07Whole brain
https://books.google.com/books?id=XTUYCwAAQBAJ&pg=PA177&lpg=PA177&dq=density+of+neurons+in+reptile+brain&source=bl&ots=In1mgZmQJY&sig=dGCCUiJPKTKNftmmiFpfxbRiqZU&hl=en&sa=X&ved=0ahUKEwju0eOXo5HVAhUS22MKHUV_C7YQ6AEIXDAJ#v=onepage&q=density%20of%20neurons%20in%20reptile%20brain&f=false
This actually seems wrong - a crocodile has about as many neurons as a mouse?
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Green lizard2.00E+06Whole brain
https://faculty.washington.edu/chudler/facts.html
Crocodile source found a neural density of 25000 neurons/mg. Multipled by the source's claim of 80 mg in green lizard brain. I think this might be too low.
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Amphibia
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TeleostZebrafish (adult) (Danio rerio)5.00E+06SE: 8E5
Total cells in whole brain
http://www.sciencedirect.com/science/article/pii/S0306452207001455
Brain was sectioned, sampled, digested with collegenase. Cells were stained with methylene blue and counted. 50% of cells were neurons.
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InsectaHoneybee9.60E+05
http://www.sciencedirect.com/science/article/pii/S1364661300016016#BIB3
Unclear
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Fruit fly (drosophilia melanogaster)
1.00E+05Whole brain
http://www.sciencedirect.com/science/article/pii/S0960982210015770
Unclear
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2.00E+05Whole brain
https://books.google.com/books?id=LWI_AAAAQBAJ&pg=PA121#v=onepage&q&f=false
Unclear
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Megaphragma (tiny parasitic wasps)
7.40E+03Whole body
https://www.researchgate.net/profile/Alexey_Polilov/publication/51793980_The_smallest_insects_evolve_anucleate_neurons/links/54566cf80cf2bccc490f28ef/The-smallest-insects-evolve-anucleate-neurons.pdf
Histological sections, which were stained and counted.
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Feather-winged beetles (nanosellini)
5.00E+04Whole body
https://www.researchgate.net/publication/225659105_Anatomy_of_the_smallest_Coleoptera_featherwing_beetles_of_the_tribe_Nanosellini_Coleoptera_Ptiliidae_and_limits_of_insect_miniaturization?el=1_x_8&enrichId=rgreq-f3e4ad4d3b9a796d81514388b1664b0e-XXX&enrichSource=Y292ZXJQYWdlOzUxNzkzOTgwO0FTOjE1OTEyNjU1NDQyMzI5NkAxNDE0OTUwMTM1OTQz
Sectioned and counted
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SpringtailsSpringtails5.80E+03
http://reducing-suffering.org/net-impact-vegetarianism-factory-farm-suffering-vs-invertebrates-pasture-fields/#R
Estimate from comparison to fruit fly size
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CrustaceaCopepod (Dactylopusia) (larval)4.00E+02Whole body
http://www.stri.si.edu/sites/publications/PDFs/2011_Eberhard_Wcislo_AdvIns_Physiol.pdf
Unclear, personal communication from T. Lacalli.
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1 mm copepod (adult)7.27E+02Whole body
According to a copepod breeding resource, http://www.fao.org/docrep/003/W3732E/w3732e0t.htm "The harpacticoid Tisbe holothuriae grows from a nauplius size of 55 µm to an adult size of more than 180 µm". The copepod studied w/r/t brain size was harpacticoid. According to http://www.sfrc.ufl.edu/planktonweb/taxonomy.htm , copepods are commonly 0.5 mm - 2 mm long, so 1 mm was used. Assuming the 55 - 100 µm growth in length correlateds to an 18.2x increase in brain size as well, 400 x 1.82 = 728 neurons.
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ArachnidaMite (Phytoseiidae persimilis)1.00E+04Cortex
https://www.ncbi.nlm.nih.gov/pubmed/17242982
Nucleic acid label YOYO-1, confocal laser scanning microscopy
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MolluscaOctopus4.20E+07Whole brain
https://books.google.com/books?id=LWI_AAAAQBAJ&pg=PA121#v=onepage&q&f=false
Unclear
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GastrotrichaGastrotrichs1.00E+02Whole body
https://books.google.com/books?id=hwCTBgAAQBAJ&pg=PA24&lpg=PA24#v=onepage&q&f=false
Based on estimating neuron count in individual features. While the book notes "it cannot be said with certainty how many neurons consitute the brain of Gastrotricha", the brain seems to contain around 50, and the whole body count appears to be less than 100.
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TODO:
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Rotifers
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A better copepod source would be good but may not exist
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Ants
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Antarctic krill
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Earthworms
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