Editing Brain (section)

==== Reptiles ====
[[File:Comparative_zoology,_structural_and_systematic_-_for_use_in_schools_and_colleges_(1883)_(20482913440).jpg|thumb|394x394px|Anatomical comparison between the brain of a lizard (A and C) and the brain of a turkey (B and D). Abbreviations: ''Olf, olfactory lobes; Hmp, cerebral hemispheres; Pn, pineal gland ; Mb, optic lobes of the middle brain ; Cb, cerebellum; MO, medulla oblongata; ii, optic nerves; iv and vi, nerves for the muscles of the eye; Py, pituitary body.''[[File:Origin_of_Vertebrates_Fig_019.png|center|thumb|384x384px]]Comparison of Vertebrate Brains: Mammalian, Reptilian, Amphibian, Teleost, and Ammocoetes. ''CB., cerebellum; PT., pituitary body; PN., pineal body; C. STR., corpus striatum; G.H.R., right ganglion habenulæ. I., olfactory; II., optic nerves.'']]
Modern [[reptile]]s and [[mammal]]s diverged from a common ancestor around 320 million years ago.<ref name=":1">{{Cite journal |last1=Reiter |first1=Sam |last2=Liaw |first2=Hua-Peng |last3=Yamawaki |first3=Tracy M. |last4=Naumann |first4=Robert K. |last5=Laurent |first5=Gilles |date=2017 |title=On the Value of Reptilian Brains to Map the Evolution of the Hippocampal Formation |url=https://www.karger.com/Article/FullText/478693 |journal=Brain, Behavior and Evolution |language=english |volume=90 |issue=1 |pages=41–52 |doi=10.1159/000478693 |issn=0006-8977 |pmid=28866680}}</ref> The number of extant reptiles far exceeds the number of mammalian species, with 11,733 recognized species of reptiles<ref>{{Cite web |title=Species Statistics Aug 2019 |url=http://www.reptile-database.org/db-info/SpeciesStat.html |access-date=2022-12-06 |website=www.reptile-database.org}}</ref> compared to 5,884 extant mammals.<ref>{{Cite web |year=2022 |title=The IUCN Red List of Threatened Species. Version 2022-1 - Summary Statistics |url=https://www.iucnredlist.org/resources/summary-statistics |access-date=December 6, 2022 |website=IUCN Red List |issn=2307-8235}}</ref> Along with the species diversity, reptiles have diverged in terms of external morphology, from [[Slender glass lizard|limbless]] to [[Draco (lizard)|tetrapod gliders]] to [[Turtle|armored chelonians]], reflecting adaptive radiation to a diverse array of environments.<ref name=":9">{{Cite journal |last1=Nomura |first1=Tadashi |last2=Kawaguchi |first2=Masahumi |last3=Ono |first3=Katsuhiko |last4=Murakami |first4=Yasunori |date=March 2013 |title=Reptiles: A New Model for Brain Evo-Devo Research: REPTILES FOR EVO-DEVO RESEARCH |url=https://onlinelibrary.wiley.com/doi/10.1002/jez.b.22484 |journal=Journal of Experimental Zoology Part B: Molecular and Developmental Evolution |language=en |volume=320 |issue=2 |pages=57–73 |doi=10.1002/jez.b.22484|pmid=23319423 }}</ref><ref name=":0">{{Cite journal |last1=Salas |first1=Cosme |last2=Broglio |first2=Cristina |last3=Rodríguez |first3=Fernando |date=2003 |title=Evolution of Forebrain and Spatial Cognition in Vertebrates: Conservation across Diversity |url=https://www.karger.com/Article/FullText/72438 |journal=Brain, Behavior and Evolution |language=english |volume=62 |issue=2 |pages=72–82 |doi=10.1159/000072438 |issn=0006-8977 |pmid=12937346}}</ref>

Morphological differences are reflected in the nervous system [[phenotype]], such as: absence of lateral motor column neurons in snakes, which innervate limb muscles controlling limb movements; absence of motor neurons that innervate trunk muscles in tortoises; presence of innervation from the trigeminal nerve to [[Infrared sensing in snakes|pit organs]] responsible to infrared detection in snakes.<ref name=":9" /> Variation in size, weight, and shape of the brain can be found within reptiles.<ref name=":6">{{Cite journal |last=Northcutt |first=R. Glenn |date=2013 |title=Variation in Reptilian Brains and Cognition |url=https://www.karger.com/Article/FullText/351996 |journal=Brain, Behavior and Evolution |language=english |volume=82 |issue=1 |pages=45–54 |doi=10.1159/000351996 |issn=0006-8977 |pmid=23979455}}</ref> For instance, crocodilians have the largest brain volume to body weight proportion, followed by turtles, lizards, and snakes. Reptiles vary in the investment in different brain sections. Crocodilians have the largest telencephalon, while snakes have the smallest. Turtles have the largest diencephalon per body weight whereas crocodilians have the smallest. On the other hand, lizards have the largest mesencephalon.<ref name=":6" />

Yet their brains share several characteristics revealed by recent anatomical, molecular, and [[Ontogeny|ontogenetic]] studies.<ref name=":3">{{Cite journal |last1=Naumann |first1=Robert K. |last2=Ondracek |first2=Janie M. |last3=Reiter |first3=Samuel |last4=Shein-Idelson |first4=Mark |last5=Tosches |first5=Maria Antonietta |last6=Yamawaki |first6=Tracy M. |last7=Laurent |first7=Gilles |date=2015-04-20 |title=The reptilian brain |journal=Current Biology |language=English |volume=25 |issue=8 |pages=R317–R321 |doi=10.1016/j.cub.2015.02.049 |issn=0960-9822 |pmc=4406946 |pmid=25898097|bibcode=2015CBio...25.R317N }}</ref><ref name=":4">{{Cite journal |last1=Hain |first1=David |last2=Gallego-Flores |first2=Tatiana |last3=Klinkmann |first3=Michaela |last4=Macias |first4=Angeles |last5=Ciirdaeva |first5=Elena |last6=Arends |first6=Anja |last7=Thum |first7=Christina |last8=Tushev |first8=Georgi |last9=Kretschmer |first9=Friedrich |last10=Tosches |first10=Maria Antonietta |last11=Laurent |first11=Gilles |date=2022-09-02 |title=Molecular diversity and evolution of neuron types in the amniote brain |url=https://www.science.org/doi/10.1126/science.abp8202 |journal=Science |language=en |volume=377 |issue=6610 |pages=eabp8202 |doi=10.1126/science.abp8202 |pmid=36048944 |issn=0036-8075}}</ref><ref>{{Cite journal |last1=Tosches |first1=Maria Antonietta |last2=Yamawaki |first2=Tracy M. |last3=Naumann |first3=Robert K. |last4=Jacobi |first4=Ariel A. |last5=Tushev |first5=Georgi |last6=Laurent |first6=Gilles |date=2018-05-25 |title=Evolution of pallium, hippocampus, and cortical cell types revealed by single-cell transcriptomics in reptiles |url=https://www.science.org/doi/10.1126/science.aar4237 |journal=Science |language=en |volume=360 |issue=6391 |pages=881–888 |doi=10.1126/science.aar4237 |pmid=29724907 |bibcode=2018Sci...360..881T |issn=0036-8075}}</ref> Vertebrates share the highest levels of similarities during [[Embryology|embryological]] development, controlled by [[Conserved sequence|conserved]] [[transcription factor]]s and [[Developmental signaling center|signaling centers]], including gene expression, morphological and cell type differentiation.<ref name=":3" /><ref name=":9" /><ref>{{Cite journal |last1=Blanton |first1=Mark G. |last2=Kriegstein |first2=Arnold R. |date=1991-08-22 |title=Morphological differentiation of distinct neuronal classes in embryonic turtle cerebral cortex |url=https://onlinelibrary.wiley.com/doi/10.1002/cne.903100405 |journal=The Journal of Comparative Neurology |language=en |volume=310 |issue=4 |pages=550–570 |doi=10.1002/cne.903100405 |pmid=1719040 |issn=0021-9967}}</ref> In fact, high levels of transcriptional factors can be found in all areas of the brain in reptiles and mammals, with shared neuronal clusters enlightening brain evolution.<ref name=":4" /> Conserved transcription factors elucidate that evolution acted in different areas of the brain by either retaining similar morphology and function, or diversifying it.<ref name=":3" /><ref name=":4" />

Anatomically, the reptilian brain has less subdivisions than the mammalian brain, however it has numerous conserved aspects including the organization of the spinal cord and cranial nerve, as well as elaborated brain pattern of organization.<ref name=":5">{{Cite book |last1=William |first1=Butler |first2=Ann B. |last2=Hodos |url=http://worldcat.org/oclc/489018202 |title=Comparative vertebrate neuroanatomy : evolution and adaptation |date=2005 |publisher=Wiley-Liss |isbn=0-471-21005-6 |oclc=489018202}}</ref> Elaborated brains are characterized by migrated neuronal cell bodies away from the periventricular matrix, region of neuronal development, forming organized nuclear groups.<ref name=":5" /> Aside from [[reptile]]s and [[mammal]]s, other vertebrates with elaborated brains include [[hagfish]], [[Shark|galeomorph sharks]], [[Skate (fish)|skates]], [[Batoidea|rays]], [[teleost]]s, and [[bird]]s.<ref name=":5" /> Overall elaborated brains are subdivided in forebrain, midbrain, and hindbrain.

The hindbrain coordinates and integrates sensory and motor inputs and outputs responsible for, but not limited to, walking, swimming, or flying. It contains input and output axons interconnecting the spinal cord, midbrain and forebrain transmitting information from the external and internal environments.<ref name=":5" /> The midbrain links sensory, motor, and integrative components received from the hindbrain, connecting it to the forebrain. The tectum, which includes the optic tectum and torus semicircularis, receives auditory, visual, and somatosensory inputs, forming integrated maps of the sensory and visual space around the animal.<ref name=":5" /> The tegmentum receives incoming sensory information and forwards motor responses to and from the forebrain. The isthmus connects the hindbrain with midbrain. The forebrain region is particularly well developed, is further divided into diencephalon and telencephalon. Diencephalon is related to regulation of eye and body movement in response to visual stimuli, sensory information, [[circadian rhythm]]s, olfactory input, and [[autonomic nervous system]].Telencephalon is related to control of movements, neurotransmitters and neuromodulators responsible for integrating inputs and transmitting outputs are present, sensory systems, and cognitive functions.<ref name=":5" />