Editing Motor cortex (section)

==Evolution==
[[File:M1 microcircuit model.jpg|thumb|A biophysically realistic model of the mouse primary motor cortex microcircuit representing a cylindrical volume of 300  μm   diameter: 3D visualization, connectivity, dimensions, and neuronal densities, classes, and morphologies<ref>{{cite journal |last1=Dura-Bernal |first1=Salvador |last2=Neymotin |first2=Samuel A. |last3=Suter |first3=Benjamin A. |last4=Dacre |first4=Joshua |last5=Moreira |first5=Joao V.S. |last6=Urdapilleta |first6=Eugenio |last7=Schiemann |first7=Julia |last8=Duguid |first8=Ian |last9=Shepherd |first9=Gordon M.G. |last10=Lytton |first10=William W. |title=Multiscale model of primary motor cortex circuits predicts in vivo cell-type-specific, behavioral state-dependent dynamics |journal=Cell Reports |date=June 2023 |volume=42 |issue=6 |pages=112574 |doi=10.1016/j.celrep.2023.112574|doi-access=free |pmid=37300831 |pmc=10592234 }}</ref>]]
Mammals evolved from mammal-like reptiles over 200 million years ago.<ref name=Kass>{{cite journal | author=Kaas, J.H. | year=2004 | title=Evolution of somatosensory and motor cortex in primates. | journal=The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology | volume=281 | pages=1148–1156 | pmid=15470673 | doi=10.1002/ar.a.20120 | issue=1| doi-access=free }}</ref> These early mammals developed several novel brain functions most likely due to the novel sensory processes that were necessary for the nocturnal niche that these mammals occupied.<ref name="Jerison">{{cite book |author=Jerison, Harry |title=Evolution of the Brain and Intelligence |publisher=Academic Press Inc. |location=Elsevier |year=1973 }}</ref> These animals most likely had a somatomotor cortex, where somatosensory information and motor information were processed in the same cortical region. This allowed for the acquisition of only simple motor skills, such as quadrupedal locomotion and striking of predators or prey. Placental mammals evolved a discrete motor cortex about 100 [[mya (unit)|mya]].<ref name="Kass"/> According to the principle of proper mass, "the mass of neural tissue controlling a particular function is appropriate to the amount of information processing involved in performing the function.<ref name="Jerison"/>" This suggests that the development of a discrete motor cortex was advantageous for placental mammals, and the motor skills that these organisms acquired were more complex than their early-mammalian ancestors. Further, this motor cortex was necessary for the arboreal lifestyles of our primate ancestors.

Enhancements to the motor cortex (and the presence of opposable thumbs and stereoscopic vision) were evolutionarily selected to prevent primates from making mistakes in the dangerous motor skill of leaping between tree branches (Cartmill, 1974; Silcox, 2007). As a result of this pressure, the motor system of arboreal primates has a disproportionate degree of somatotopic representation of the hands and feet, which is essential for grasping (Nambu, 2011; Pons et al., 1985; Gentilucci et al., 1988).