Editing Brain (section)

==== Mammals ====
The most obvious difference between the brains of mammals and other vertebrates is their size. On average, a mammal has a brain roughly twice as large as that of a bird of the same body size, and ten times as large as that of a reptile of the same body size.<ref name=Northcutt2002>{{cite journal |last=Northcutt |first=RG |title=Understanding vertebrate brain evolution |journal=Integrative and Comparative Biology |volume=42 |pages=743–756 |pmid=21708771 |doi=10.1093/icb/42.4.743 |year=2002 |issue=4|doi-access=free }}</ref>

Size, however, is not the only difference: there are also substantial differences in shape. The hindbrain and midbrain of mammals are generally similar to those of other vertebrates, but dramatic differences appear in the forebrain, which is greatly enlarged and also altered in structure.<ref name=Barton>{{cite journal |last1=Barton |first1=RA |title=Mosaic evolution of brain structure in mammals |year=2000 |journal=Nature |volume=405 |pages=1055–1058 |pmid=10890446 |doi=10.1038/35016580 |last2=Harvey |first2=PH |issue=6790|bibcode=2000Natur.405.1055B |s2cid=52854758 }}</ref> The cerebral cortex is the part of the brain that most strongly distinguishes mammals. In non-mammalian vertebrates, the surface of the [[cerebrum]] is lined with a comparatively simple three-layered structure called the [[pallium (neuroanatomy)|pallium]]. In mammals, the pallium evolves into a complex six-layered structure called [[neocortex]] or ''isocortex''.<ref name=Aboitiz>{{cite journal |title=The evolutionary origin of the mammalian isocortex: Towards an integrated developmental and functional approach |journal=Behavioral and Brain Sciences |year=2003 |volume=26 |pages=535–552 |pmid=15179935 |doi=10.1017/S0140525X03000128 |last1=Aboitiz |first1=F |last2=Morales |first2=D |last3=Montiel |first3=J |issue=5 |s2cid=6599761 }}</ref> Several areas at the edge of the neocortex, including the hippocampus and [[amygdala]], are also much more extensively developed in mammals than in other vertebrates.<ref name=Barton/>

The elaboration of the cerebral cortex carries with it changes to other brain areas. The [[superior colliculus]], which plays a major role in visual control of behavior in most vertebrates, shrinks to a small size in mammals, and many of its functions are taken over by visual areas of the cerebral cortex.<ref name=Northcutt2002/> The cerebellum of mammals contains a large portion (the [[neocerebellum]]) dedicated to supporting the cerebral cortex, which has no counterpart in other vertebrates.<ref>{{cite book |year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |page=531 |isbn=978-0-03-910284-5 |last1=Romer |first1=AS |last2=Parsons |first2=TS}}</ref>

In [[placental]]s, there is a wide nerve tract connecting the cerebral hemispheres called the [[corpus callosum]].

===== Primates =====
{{See also|Human brain}}

{| class="wikitable" align="right" style="margin-left: 10px;"
|+Encephalization Quotient
!Species
!EQ<ref name=Roth2005>{{cite journal |title=Evolution of the brain and Intelligence |last1=Roth |first1=G |last2=Dicke |first2=U |journal=Trends in Cognitive Sciences |volume=9 |issue=5 |pages=250–257 |year=2005 |doi=10.1016/j.tics.2005.03.005 |pmid=15866152|s2cid=14758763 }}</ref>
|-
|Human||7.4–7.8
|-
|[[Common chimpanzee]]||2.2–2.5
|-
|[[Rhesus macaque|Rhesus monkey]]||2.1
|-
|[[Bottlenose dolphin]]||4.14<ref name=Marino>{{cite journal |last=Marino |first=Lori |title=Cetacean Brain Evolution: Multiplication Generates Complexity |journal=International Society for Comparative Psychology |issue=17 |pages=1–16 |year=2004 |url=http://www.cogs.indiana.edu/spackled/2005readings/CetaceanBrainEvolution.pdf |access-date=2010-08-29 |archive-url=https://web.archive.org/web/20180916132752/http://www.cogs.indiana.edu/spackled/2005readings/CetaceanBrainEvolution.pdf |archive-date=2018-09-16 |url-status=dead }}</ref>
|-
|[[Elephant]]||1.13–2.36<ref>{{Cite journal |doi=10.1016/j.brainresbull.2006.03.016 |last1=Shoshani |first1=J |last2=Kupsky |first2=WJ |last3=Marchant |first3=GH |title=Elephant brain Part I: Gross morphology, functions, comparative anatomy, and evolution |journal=Brain Research Bulletin |volume=70 |issue=2 |pages=124–157 |year=2006 |pmid=16782503|s2cid=14339772 }}</ref>
|-
|[[Dog]]||1.2
|-
|[[Horse]]||0.9
|-
|[[Rat]]||0.4
<!--|-
|colspan="2" style="text-align: left;" |EQ relative to the cat as standard species: EQ(cat)=1-->
|-
|}

The [[human brain|brains of humans]] and other [[primate]]s contain the same structures as the brains of other mammals, but are generally larger in proportion to body size.<ref name=Finlay>{{cite journal |year=2001 |title=Developmental structure in brain evolution |journal=Behavioral and Brain Sciences |volume=24 |pages=263–308 |pmid=11530543 |last1=Finlay |first1=BL |last2=Darlington |first2=RB |last3=Nicastro |first3=N |issue=2 |doi=10.1017/S0140525X01003958|s2cid=20978251 }}</ref> The [[encephalization quotient]] (EQ) is used to compare brain sizes across species. It takes into account the nonlinearity of the brain-to-body relationship.<ref name=Roth2005/> Humans have an average EQ in the 7-to-8 range, while most other primates have an EQ in the 2-to-3 range. Dolphins have values higher than those of primates other than humans,<ref name=Marino/> but nearly all other mammals have EQ values that are substantially lower.

Most of the enlargement of the primate brain comes from a massive expansion of the cerebral cortex, especially the [[prefrontal cortex]] and the parts of the cortex involved in [[Visual perception|vision]].<ref>{{cite book|last=Calvin|first=William H.|url=https://archive.org/details/howbrainsthinkev00calv|title=How Brains Think|publisher=BasicBooks|year=1996|isbn=978-0-465-07278-1|edition=1st|location=New York, NY |url-access=registration}}</ref> The visual processing network of primates includes at least 30 distinguishable brain areas, with a complex web of interconnections. It has been estimated that visual processing areas occupy more than half of the total surface of the primate neocortex.<ref name = Sereno1995>{{cite journal |doi=10.1126/science.7754376 |last1=Sereno |first1=MI |last2=Dale |first2=AM |last3=Reppas |first3=AM |last4=Kwong |first4=KK |last5=Belliveau |first5=JW |last6=Brady |first6=TJ |last7=Rosen |first7=BR |last8=Tootell |first8=RBH |year=1995 |title=Borders of multiple visual areas in human revealed by functional magnetic resonance imaging |journal=Science |volume=268 |issue=5212 |pages=889–893 |url=http://www.cogsci.ucsd.edu/~sereno/papers/HumanRetin95.pdf |archive-url=https://web.archive.org/web/20060523153637/http://cogsci.ucsd.edu/~sereno/papers/HumanRetin95.pdf |archive-date=2006-05-23 |url-status=live |pmid=7754376 |bibcode=1995Sci...268..889S}}</ref> The [[prefrontal cortex]] carries out functions that include [[foresight (psychology)|planning]], [[working memory]], [[motivation]], [[attention]], and [[executive functions|executive control]]. It takes up a much larger proportion of the brain for primates than for other species, and an especially large fraction of the human brain.<ref>{{cite book|last=Fuster|first=Joaquín M.|url=https://archive.org/details/prefrontalcortex00fust_846|title=The Prefrontal Cortex|publisher=Elsevier|year=2008|isbn=978-0-12-373644-4|edition=4th |pages=[https://archive.org/details/prefrontalcortex00fust_846/page/n15 1]–7|url-access=limited}}</ref>