Editing Triune brain (section)

== Status of the model ==
MacLean originally formulated the triune brain hypothesis in the 1960s, drawing on comparative neuroanatomical work done by [[Ludwig Edinger]], [[Elizabeth C. Crosby]] and Charles Judson Herrick early in the twentieth century.<ref>{{cite journal |last1=Reiner |first1=A. |title=The Triune Brain in Evolution. Role in Paleocerebral Functions. Paul D. MacLean. Plenum, New York, 1990. xxiv, 672 pp., illus. $75 |journal=Science |date=12 October 1990 |volume=250 |issue=4978 |pages=303–305 |doi=10.1126/science.250.4978.303-a |pmid=17797318 |s2cid=11754163 }}</ref><ref name = PrinciplesBrainEvolution>[[Georg F. Striedter|Striedter, G. F.]] (2005) ''Principles of Brain Evolution.'' Sinauer Associates.{{page needed|date=November 2020}}</ref> The 1980s saw a rebirth of interest in comparative neuroanatomy, motivated in part by the availability of a variety of new neuroanatomical techniques for charting the circuitry of animal brains. Subsequent findings according to human brain evolution expert Terrence Deacon, have refined the traditional neuroanatomical ideas upon which MacLean based his hypothesis. Deacon mentioned that 'the evolutionary addition of different parts of the brain is simply not realistic. However, all the parts of the brain were already existing, they were just further developed upon as the homosapien species evolved and gained life experiences.'<ref>{{Cite web |title=A theory abandoned but still compelling |url=https://medicine.yale.edu/news/yale-medicine-magazine/article/a-theory-abandoned-but-still-compelling/ |access-date=2022-09-28 |website=medicine.yale.edu |language=en}}</ref> 

For example, the basal ganglia (structures derived from the floor of the forebrain and making up MacLean's reptilian complex) were shown to take up a much smaller portion of the forebrains of reptiles and birds (together called [[sauropsids]]) than previously supposed, and to exist in [[amphibians]] and [[fish]] as well as [[mammals]] and sauropsids. Because the basal ganglia are found in the forebrains of all modern vertebrates, they most likely date to the common evolutionary ancestor of the vertebrates, more than 500 million years ago, rather than to the origin of reptiles.{{citation needed|date=November 2020}}

Recent behavioral studies do not support the traditional view of sauropsid behavior as stereotyped and ritualistic (as in MacLean's reptilian complex). Birds have been shown to possess highly sophisticated cognitive abilities, such as the toolmaking of the [[New Caledonian crow]] and the language-like categorization abilities of the [[grey parrot]].<ref>{{cite news | first=Paul | last=Patton |title= One World, Many Minds: Intelligence in the Animal Kingdom |url= http://www.sciam.com/article.cfm?id=one-world-many-minds |work= Scientific American |date= December 2008|access-date=29 December 2008}}</ref> Structures of the limbic system, which MacLean proposed arose in early mammals, have now been shown to exist across a range of modern vertebrates. The "paleomammalian" trait of parental care of offspring is widespread in birds and occurs in some fishes as well.  Thus, like the basal ganglia, the evolution of these systems presumably dates to a common vertebrate ancestor.<ref name = PrinciplesBrainEvolution /><ref name="ReferenceA">Butler, A. B. and Hodos, W. Comparative Vertebrate Neuroanatomy: Evolution and Adaptation, Wiley{{page needed|date=November 2020}}</ref>

[[File:Comparative evolution of the striatum and pallium in vertebrates.png|thumb|The ratio of the brain mass devoted to the pallium increase in parallel in various vertebrates' taxa<ref>{{cite journal |last1=Boraud |first1=Thomas |last2=Leblois |first2=Arthur |last3=Rougier |first3=Nicolas P. |title=A natural history of skills |journal=Progress in Neurobiology |date=December 2018 |volume=171 |pages=114–124 |doi=10.1016/j.pneurobio.2018.08.003 |pmid=30171867 |url=https://hal.inria.fr/hal-01874690/file/A%20Natural%20History%20of%20Skills-V1.pdf }}</ref>]]

Finally, recent studies based on paleontological data or comparative anatomical evidence strongly suggest that the neocortex was already present in the earliest emerging mammals.<ref name="PrinciplesBrainEvolution"/> In addition, although non-mammals do not have a neocortex in the true sense (that is, a structure comprising part of the forebrain roof, or pallium, consisting of six characteristic layers of neurons), they possess [[Pallium (neuroanatomy)|pallial]] regions, and some parts of the pallium are considered homologous to the mammalian neocortex. While these areas lack the characteristic six neocortical layers, birds and reptiles generally possess three layers in the dorsal pallium (the homolog of the mammalian neocortex).<ref name = PrinciplesBrainEvolution /><ref name="ReferenceA"/> The [[telencephalon]] of birds and mammals makes neuroanatomical connections with other telecencephalic structures<ref name = PrinciplesBrainEvolution /> like those made by neocortex. It mediates similar functions such as perception, learning and memory, decision making, motor control, conceptual thinking.