Editing Motor cortex

{{short description|Region of the cerebral cortex}}
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| name            = Motor cortex
| Latin           = cortex motorius
| image           = Human motor cortex.jpg
| caption         = Topography of human motor cortex. Supplementary motor area labelled SMA.
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The '''motor cortex''' is the region of the [[cerebral cortex]] involved in the planning, [[motor control|control]], and execution of voluntary movements.
The motor cortex is an area of the [[frontal lobe]] located in the posterior [[precentral gyrus]] immediately anterior to the central sulcus.

[[File:Figure 35 03 04.jpg|thumb|261x261px|Motor cortex controls different muscle groups]]

==Components==
{{See also|Cerebral cortex#Motor areas}}

The motor cortex can be divided into three areas:

1. The [[primary motor cortex]] is the main contributor to generating neural impulses that pass down to the spinal cord and control the execution of movement.  However, some of the other motor areas in the brain also play a role in this function. It is located on the anterior paracentral lobule on the medial surface.

2. The [[premotor cortex]] is responsible for some aspects of motor control, possibly including the preparation for movement, the sensory guidance of movement, the spatial guidance of reaching, or the direct control of some movements with an emphasis on control of proximal and trunk muscles of the body. Located anterior to the primary motor cortex.

3. The [[supplementary motor area]] (or SMA), has many proposed functions including the internally generated planning of movement, the planning of sequences of movement, and the coordination of the two sides of the body such as in bi-manual coordination. Located on the midline surface of the hemisphere anterior to the primary motor cortex.
* The [[posterior parietal cortex]] is sometimes also considered to be part of the group of motor cortical areas; however it is best to regard it as an association cortex rather than motor. It is thought to be responsible for transforming multisensory information into motor commands, and to be responsible for some aspects of [[motor planning]], in addition to many other functions that may not be motor related.
* The [[primary somatosensory cortex]], especially the part called area 3a, which lies directly against the motor cortex, is sometimes considered to be functionally part of the motor control circuitry.

Other brain regions outside the cerebral cortex are also of great importance to motor function, most notably the [[cerebellum]], the [[basal ganglia]], [[pedunculopontine nucleus]] and the [[red nucleus]], as well as other subcortical [[nucleus (neuroanatomy)|motor nuclei]].

===The premotor cortex===
In the earliest work on the motor cortex, researchers recognized only one cortical field involved in motor control. [[Alfred Walter Campbell]]<ref name=Campbell/> was the first to suggest that there might be two fields, a "primary" motor cortex and an "intermediate precentral" motor cortex. His reasons were largely based on [[cytoarchitectonics of the cerebral cortex|cytoarchitectonics]], or the study of the appearance of the cortex under a microscope. The primary motor cortex contains cells with giant cell bodies known as "[[Betz cell]]s". These cells were mistakenly thought to be the main outputs from the cortex, sending fibers to the spinal cord.<ref name=Campbell/> It has since been found that [[Betz cell]]s account for about 2-3% of the projections from the cortex to the spinal cord, or about 10% of the projections from the primary motor cortex to the spinal cord.<ref name=Rivara&etal>{{cite journal |vauthors=Rivara CB, Sherwood CC, Bouras C, Hof PR | year=2003 | title=Stereologic characterization and spatial distribution patterns of Betz cells in the human primary motor cortex | journal=The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology | volume=270 | pages=137–151 | doi=10.1002/ar.a.10015 | pmid=12524689 | issue=2| doi-access=free }}</ref><ref name=Lassek>{{cite journal | author=Lassek, A.M. | year=1941 | title=The pyramidal tract of the monkey | journal=J. Comp. Neurol. | volume=74 | pages=193–202 | doi=10.1002/cne.900740202 | issue=2| s2cid=83536088 }}</ref> The specific function of the [[Betz cell]]s that distinguishes them from other output cells of the motor cortex remains unknown, but they continue to be used as a marker for the primary motor cortex.

Other researchers, such as [[Oskar Vogt]], [[Cécile Vogt-Mugnier]]<ref name=Vogt&Vogt/> and [[Otfrid Foerster]]<ref name=Foerster/> also suggested that motor cortex was divided into a primary motor cortex (area 4, according to [[Korbinian Brodmann|Brodmann's]]<ref name=Brodmann1909>{{cite book | author=[[Korbinian Brodmann|Brodmann, K]] | year=1909 | title=Vergleichende Lokalisationslehre der Grosshirnrinde | url=https://archive.org/details/b28062449| publisher=J.A. Barth | location=Leipzig}}</ref> naming scheme) and a higher-order motor cortex (area 6 according to [[Korbinian Brodmann]]).

[[Wilder Penfield]]<ref name=Penfield&Boldrey/><ref name=Penfield/> notably disagreed and suggested that there was no functional distinction between area 4 and area 6. In his view both were part of the same map, though area 6 tended to emphasize the muscles of the back and neck. Woolsey<ref name=Woolsey&etal>{{cite journal | last1=Woolsey|first1=C.N.|last2=Settlage|first2=P.H.|last3=Meyer|first3= D.R.|last4=Sencer|first4=W.|last5=Hamuy|first5=T.P.|last6=Travis|first6=A.M. | year=1952 | title=Pattern of localization in precentral and "supplementary" motor areas and their relation to the concept of a premotor area | journal=Association for Research in Nervous and Mental Disease |volume=30 | pages=238–264 | publisher=Raven Press | location=New York, NY}}</ref> who studied the motor map in monkeys also believed there was no distinction between primary motor and premotor. M1 was the name for the proposed single map that encompassed both the primary motor cortex and the premotor cortex.<ref name=Woolsey&etal/> Although sometimes "M1" and "primary motor cortex" are used interchangeably, strictly speaking, they derive from different conceptions of motor cortex organization.{{Citation needed|date=May 2017}}

Despite the views of Penfield and Woolsey, a consensus emerged that area 4 and area 6 had sufficiently different functions that they could be considered different cortical fields. Fulton<ref name=Fulton>{{cite journal | author=Fulton, J | year=1935 | title=A note on the definition of the "motor" and "premotor" areas | journal=Brain | volume=58 | pages=311–316 | doi=10.1093/brain/58.2.311 | issue=2}}</ref>  helped to solidify this distinction between a primary motor cortex in area 4 and a premotor cortex in area 6. As Fulton pointed out, and as all subsequent research has confirmed, both primary motor and premotor cortex project directly to the spinal cord and are capable of some direct control of movement. Fulton showed that when the primary motor cortex is damaged in an experimental animal, movement soon recovers; when the premotor cortex is damaged, movement soon recovers; when both are damaged, movement is lost and the animal cannot recover.

[[File:Motor Cortex monkey.jpg|thumb|Some commonly accepted divisions of the cortical motor system of the monkey]]

The premotor cortex is now generally divided into four sections.<ref name=Graziano&2008/><ref name=Matelli&etal>{{cite journal | last1=Matelli|first1=M.|last2=Luppino|first2=G.|last3=Rizzolati|first3=G | year=1985 | title=Patterns of cytochrome oxidase activity in the frontal agranular cortex of the macaque monkey | journal=Behav. Brain Res. | volume=18 | pages=125–136 | doi=10.1016/0166-4328(85)90068-3 | pmid=3006721 | issue=2| s2cid=41391502 }}</ref><ref name=Preuss&etal>{{cite journal | last1=Preuss|first1=T.M.|last2=Stepniewska|first2=I.|last3=Kaas|first3=J.H | year=1996 | title=Movement representation in the dorsal and ventral premotor areas of owl monkeys: a microstimulation study | journal=J. Comp. Neurol. | volume=371 | pages=649–676 | doi=10.1002/(SICI)1096-9861(19960805)371:4<649::AID-CNE12>3.0.CO;2-E | pmid=8841916 | issue=4|s2cid=37009687 | doi-access=free }}</ref> First it is divided into an upper (or dorsal) premotor cortex and a lower (or ventral) premotor cortex. Each of these is further divided into a region more toward the front of the brain (rostral premotor cortex) and a region more toward the back (caudal premotor cortex). A set of acronyms are commonly used: PMDr (premotor dorsal, rostral), PMDc, PMVr, PMVc. Some researchers use a different terminology. Field 7 or F7 denotes PMDr; F2 = PMDc; F5=PMVr; F4=PMVc.

PMDc is often studied with respect to its role in guiding reaching.<ref name=Hochermann&Wise>{{cite journal |author1=Hochermann, S.  |author2=Wise, S.P  | year=1991 | title=Effects of hand movement path on motor cortical activity in awake, behaving rhesus monkeys | journal=Exp. Brain Res. | volume=83 | pages=285–302 | pmid=2022240 | issue=2 | doi=10.1007/bf00231153|s2cid=38010957 }}</ref><ref name=Cisek&Kalaska>{{cite journal |author1=Cisek, P  |author2=Kalaska, J.F  | year=2005 | title=Neural correlates of reaching decisions in dorsal premotor cortex: specification of multiple direction choices and final selection of action | journal=Neuron | volume=45 | pages=801–814 | doi=10.1016/j.neuron.2005.01.027 | pmid=15748854 | issue=5|s2cid=15183276 | doi-access=free }}</ref><ref name=Churchland&etal>{{cite journal | last=Churchland | first=M. M. | title=Neural Variability in Premotor Cortex Provides a Signature of Motor Preparation | journal=Journal of Neuroscience | publisher=Society for Neuroscience | volume=26 | issue=14 | date=5 April 2006 | issn=0270-6474 | doi=10.1523/jneurosci.3762-05.2006|doi-access=free | pages=3697–3712| pmid=16597724 | pmc=6674116 }}</ref> Neurons in PMDc are active during reaching. When monkeys are trained to reach from a central location to a set of target locations, neurons in PMDc are active during the preparation for the reach and also during the reach itself. They are broadly tuned, responding best to one direction of reach and less well to different directions. Electrical stimulation of the PMDc on a behavioral time scale was reported to evoke a complex movement of the shoulder, arm, and hand that resembles reaching with the hand opened in preparation to grasp.<ref name=Graziano&2008/>

PMDr may participate in learning to associate arbitrary sensory stimuli with specific movements or learning arbitrary response rules.<ref name=Weinrich&etal>{{cite journal | last1=WEINRICH | first1=M. | last2=WISE | first2=S. P | last3=MAURITZ | first3=K.-H. | title=A Neurophysiological Study of the Premotor Cortex in the Rhesus Monkey | journal=Brain | publisher=Oxford University Press (OUP) | volume=107 | issue=2 | year=1984 | issn=0006-8950 | doi=10.1093/brain/107.2.385 | pages=385–414| pmid=6722510 }}</ref><ref name=Brasted&Wise>{{cite journal |author1=Brasted, P.J.  |author2=Wise, S.P  | year=2004 | title=Comparison of learning-related neuronal activity in the dorsal premotor cortex and striatum | journal=European Journal of Neuroscience | volume=19 | pages=721–740 | doi=10.1111/j.0953-816X.2003.03181.x | issue=3 | pmid=14984423|s2cid=30681663 |url=https://zenodo.org/record/1230597 }}</ref><ref name=Muhammad&etal>{{cite journal | author=Muhammad, R., Wallis, J.D. and Miller, E.K | title=A comparison of abstract rules in the prefrontal cortex, premotor cortex, inferior temporal cortex, and striatum | journal=J. Cogn. Neurosci. | volume=18 | pages=974–989 | doi=10.1162/jocn.2006.18.6.974 | year=2006 | issue=6 | pmid=16839304| s2cid=10212467 }}</ref> In this sense it may resemble the prefrontal cortex more than other motor cortex fields. It may also have some relation to eye movement. Electrical stimulation in the PMDr can evoke eye movements<ref name=Bruce&etal>{{cite journal |vauthors=Bruce CJ, Goldberg ME, Bushnell MC, Stanton GB | year=1985 | title=Primate frontal eye fields. II. Physiological and anatomical correlates of electrically evoked eye movements | journal=J. Neurophysiol. | volume=54 | pages=714–734 | pmid=4045546 | issue=3 | doi=10.1152/jn.1985.54.3.714}}</ref> and neuronal activity in the PMDr can be modulated by eye movement.<ref name=Boussaoud&1995>{{cite journal | author=Boussaoud D | year=1985 | title=Primate premotor cortex: modulation of preparatory neuronal activity by gaze angle | journal=J. Neurophysiol. | volume=73 | pages=886–890 | pmid=7760145 | issue=2 | doi=10.1152/jn.1995.73.2.886}}</ref>

PMVc or F4 is often studied with respect to its role in the sensory guidance of movement. Neurons here are responsive to tactile stimuli, visual stimuli, and auditory stimuli.<ref name=Rizzolatti&etal1981>{{cite journal | last1=Rizzolatti | first1=Giacomo | last2=Scandolara | first2=Cristiana | last3=Matelli | first3=Massimo | last4=Gentilucci | first4=Maurizio | title=Afferent properties of periarcuate neurons in macaque monkeys. II. Visual responses | journal=Behavioural Brain Research | volume=2 | issue=2 | year=1981 | issn=0166-4328 | doi=10.1016/0166-4328(81)90053-x| pmid=7248055| s2cid=4028658 | pages=147–163}}</ref><ref name=Fogassi&etal1996>{{cite journal | last1=Fogassi | first1=L. | last2=Gallese | first2=V. | last3=Fadiga | first3=L. | last4=Luppino | first4=G. | last5=Matelli | first5=M. | last6=Rizzolatti | first6=G. | title=Coding of peripersonal space in inferior premotor cortex (area F4) | journal=Journal of Neurophysiology| volume=76 | issue=1 | date=1 July 1996 | issn=0022-3077 | doi=10.1152/jn.1996.76.1.141| pmid=8836215 | pages=141–157}}</ref><ref name=Graziano&etal&1994>{{cite journal | author=[[Michael Graziano|Graziano, M.S.A.]], Yap, G.S. and Gross, C.G | year=1994 | title=Coding of visual space by premotor neurons | journal=Science | volume=266 | pages=1054–1057 | doi=10.1126/science.7973661 | pmid=7973661 | issue=5187| bibcode=1994Sci...266.1054G | url=http://wexler.free.fr/library/files/graziano%20(1994)%20coding%20of%20visual%20space%20by%20premotor%20neurons.pdf }}</ref><ref name=Graziano&etal&1999>{{cite journal | author=[[Michael Graziano|Graziano, M.S.A.]], Reiss, L.A. and Gross, C.G | year=1999 | title=A neuronal representation of the location of nearby sounds | journal=Nature | volume=397 | pages=428–430 | doi=10.1038/17115 | pmid=9989407 | issue=6718| bibcode=1999Natur.397..428G | s2cid=4415358 }}</ref> These neurons are especially sensitive to objects in the space immediately surrounding the body, in so-called peripersonal space. Electrical stimulation of these neurons causes an apparent defensive movement as if protecting the body surface.<ref name=Graziano&Taylor&Moore>{{cite journal | author=[[Michael Graziano|Graziano, M.S.A.]], Taylor, C.S.R. and Moore, T. | year=2002 | title=Complex movements evoked by microstimulation of precentral cortex | journal=Neuron | volume=34 | pages=841–851 | doi=10.1016/S0896-6273(02)00698-0 | pmid=12062029 | issue=5| s2cid=3069873 | doi-access=free }}</ref><ref name=Cooke&Graziano>{{cite journal | author=Cooke, D.F. and [[Michael Graziano|Graziano, M.S.A]] | year=2004 | title=Super-flinchers and nerves of steel: Defensive movements altered by chemical manipulation of a cortical motor area | journal=Neuron | volume=43 | pages=585–593 | pmid=15312656 | issue=4 | doi=10.1016/j.neuron.2004.07.029| s2cid=16222051 | doi-access=free }}</ref> This premotor region may be part of a larger circuit for maintaining a margin of safety around the body and guiding movement with respect to nearby objects.<ref name=Graziano&Cooke>{{cite journal | author=[[Michael Graziano|Graziano, M.S.A.]] and Cooke, D.F. | year=2006 | title=Parieto-frontal interactions, personal space, and defensive behavior | journal=Neuropsychologia | volume=44 | pages=845–859 | doi=10.1016/j.neuropsychologia.2005.09.009 | pmid=16277998 | issue=6| s2cid=11368801 }}</ref>

PMVr or F5 is often studied with respect to its role in shaping the hand during grasping and in interactions between the hand and the mouth.<ref name=Rizzolatti&etal&1988>{{cite journal | author=Rizzolatti, G., Camarda, R., Fogassi, L., Gentilucci, M., Luppino, G. and Matelli, M | year=1988 | title=Functional organization of inferior area 6 in the macaque monkey. II. Area F5 and the control of distal movements | journal=Exp. Brain Res. | volume=71 | pages=491–507 | pmid=3416965 | issue=3 | doi=10.1007/bf00248742| s2cid=26064832 }}</ref><ref name=Murata&etal>{{cite journal | author=Murata, A., Fadiga, L., Fogassi, L., Gallese, V. Raos, V and Rizzolatti, G | year=1997 | title=Object representation in the ventral premotor cortex (area F5) of the monkey | journal=J. Neurophysiol. | volume=78 | issue=4 | pages=2226–22230 | doi=10.1152/jn.1997.78.4.2226 | pmid=9325390}}</ref> Electrical stimulation of at least some parts of F5, when the stimulation is applied on a behavioral time scale, evokes a complex movement in which the hand moves to the mouth, closes in a grip, orients such that the grip faces the mouth, the neck turns to align the mouth to the hand, and the mouth opens.<ref name=Graziano&2008/><ref name=Graziano&Taylor&Moore/>

[[Mirror neurons]] were first discovered in area F5 in the monkey brain by Rizzolatti and colleagues.<ref name=diPellegrino&etal>{{cite journal | author=di Pellegrino, G., Fadiga, L., Fogassi, L., Gallese, V. and Rizzolatti, G | year=1992 | title=Understanding motor events: a neurophysiological study | journal=Exp. Brain Res. | volume=91 | pages=176–180 | pmid=1301372 | issue=1 | doi=10.1007/bf00230027| s2cid=206772150 }}</ref><ref name=Rizzolatti&Sinigaglia>{{cite journal |author1=Rizzolatti, G.  |author2=Sinigaglia, C  | year=2010 | title=The functional role of the parieto-frontal mirror circuit: interpretations and misinterpretations | journal=Nature Reviews Neuroscience | volume=11 | pages=264–274 | doi=10.1038/nrn2805 | pmid=20216547 | issue=4|hdl=2434/147582 |s2cid=143779 | url=https://air.unimi.it/bitstream/2434/147582/2/Rizzolatti%26Sinigaglia2010.pdf | hdl-access=free }}</ref> These neurons are active when the monkey grasps an object. Yet the same neurons become active when the monkey watches an experimenter grasp an object in the same way. The neurons are therefore both sensory and motor. Mirror neurons are proposed to be a basis for understanding the actions of others by internally imitating the actions using one's own motor control circuits.

===The supplementary motor cortex===
Penfield<ref name=Penfield&Welch>{{cite journal |author1=Penfield, W.  |author2=Welch, K  | year=1951 | title=The supplementary motor area of the cerebral cortex: A clinical and experimental study | journal=A.M.A. Arch. Neurol. Psychiatry | volume=66 | pages=289–317 | pmid = 14867993 | doi=10.1001/archneurpsyc.1951.02320090038004 | issue=3}}</ref> described a cortical motor area, the supplementary motor area (SMA), on the top or dorsal part of the cortex. Each neuron in the SMA may influence many muscles, many body parts, and both sides of the body.<ref name=Gould&etal>{{cite journal | author=Gould, H.J. III, Cusick, C.G., Pons, T.P. and Kaas, J.H | year=1996 | title=The relationship of corpus callosum connections to electrical stimulation maps of motor, supplementary motor, and the frontal eye fields in owl monkeys | journal=J. Comp. Neurol. | volume=247 | pages=297–325 | pmid=3722441 | issue=3 | doi=10.1002/cne.902470303| s2cid=21185898 }}</ref><ref name=Luppino&etal>{{cite journal | author=Luppino, G., Matelli, M., Camarda, R.M., Gallese, V. and Rizzolatti, G | year=1991 | title=Multiple representations of body movements in mesial area 6 and the adjacent cingulate cortex: an intracortical microstimulation study in the macaque monkey | journal=J. Comp. Neurol. | volume=311 | pages=463–482 | doi=10.1002/cne.903110403 | pmid=1757598 | issue=4| s2cid=25297539 }}</ref><ref name=Mitz&Wise>{{cite journal |author1=Mitz, A.R.  |author2=Wise, S.P.  | year=1987 | title=The somatotopic organization of the supplementary motor area: intracortical microstimulation mapping | journal=J. Neurosci. | volume=7 | pages=1010–1021 | pmid=3572473 | issue=4 | pmc=6568999 | doi=10.1523/JNEUROSCI.07-04-01010.1987}}</ref> The map of the body in SMA is therefore extensively overlapping. SMA projects directly to the spinal cord and may play some direct role in the control of movement.<ref name=He&etal>{{cite journal | author=He, S.Q., Dum, R.P. and Strick, P.L | year=1995 | title=Topographic organization of corticospinal projections from the frontal lobe: motor areas on the medial surface of the hemisphere | journal=J. Neurosci. | volume=15 | pages=3284–3306 | pmid=7538558 | issue=5 Pt 1 | pmc=6578253 | doi=10.1523/JNEUROSCI.15-05-03284.1995}}</ref>

Based on early work using brain imaging techniques in the human brain, Roland<ref name=Roland&etal>{{cite journal | author=Roland, P.E., Larsen, B., Lassen, N.A. and Skinhoj, E | year=1980 | title=Supplementary motor area and other cortical areas in organization of voluntary movements in man | journal=J. Neurophysiol. | volume=43 | pages=118–136 | pmid=7351547 | issue=1 | doi=10.1152/jn.1980.43.1.118}}</ref> suggested that the SMA was especially active during the internally generated plan to make a sequence of movements. In the monkey brain, neurons in the SMA are active in association with specific learned sequences of movement.<ref name=Halsband&etal>{{cite journal | author=Halsband, U., Matsuzaka, Y. and Tanji, J. | year=1994 | title=Neuronal activity in the primate supplementary, pre-supplementary and premotor cortex during externally and internally instructed sequential movements | journal=Neurosci. Res. | volume=20 | pages=149–155 | doi=10.1016/0168-0102(94)90032-9 | pmid=7808697 | issue=2| s2cid=5930996 }}</ref>

Others have suggested that, because the SMA appears to control movement bilaterally, it may play a role in inter-manual coordination.<ref name=Brinkman>{{cite journal | author=Brinkman, C | year=1981 | title=Lesions in supplementary motor area interfere with a monkey's performance of a bimanual coordination task | journal=Neurosci. Lett. | volume=27 | pages=267–270 | doi=10.1016/0304-3940(81)90441-9 | pmid=7329632 | issue=3| s2cid=41060226 }}</ref>

Yet others have suggested that, because of the direct projection of SMA to the spinal cord and because of its activity during simple movements, it may play a direct role in motor control rather than solely a high level role in planning sequences.<ref name=He&etal/><ref name=Picard&Strick>{{cite journal |author1=Picard, N.  |author2=Strick, P.L  | title=Activation of the supplementary motor area (SMA) during performance of visually guided movements | journal=Cereb. Cortex | volume=13 | pages=977–986 | doi=10.1093/cercor/13.9.977 | pmid=12902397 | year=2003 | issue=9| doi-access=free }}</ref>

On the basis of the movements evoked during electrical stimulation, it has been suggested that the SMA may have evolved in primates as a specialist in the part of the motor repertoire involving climbing and other complex locomotion.<ref name=Graziano&2008/><ref name=Graziano&Aflalo&Cooke>{{cite journal | author=[[Michael Graziano|Graziano, M.S.A.]], Aflalo, T.N. and Cooke, D.F | year=2005 | title=Arm movements evoked by electrical stimulation in the motor cortex of monkeys | journal=J. Neurophysiol. | volume=94 | pages=4209–4223 | doi=10.1152/jn.01303.2004 | pmid=16120657 | issue=6}}</ref>

Based on the pattern of projections to the spinal cord, it has been suggested that another set of motor areas may lie next to the supplementary motor area, on the medial (or midline) wall of the hemisphere.<ref name=He&etal/> These medial areas are termed the cingulate motor areas. Their functions are not yet understood.

==History==
In 1870, [[Eduard Hitzig]] and [[Gustav Fritsch]] demonstrated that electrical stimulation of certain parts of the dog brain resulted in muscular contraction on the opposite side of the body.<ref name=Fritsch&Hitzig>{{cite journal | author=[[Gustav Fritsch|Fritsch, G]] and [[Eduard Hitzig|Hitzig, E]] | title=Über die elektrische Erregbarkeit des Grosshirns | journal=Archiv für Anatomie, Physiologie und Wissenschaftliche Medicin | year=1870 | pages=300–332}} Translated in: {{cite book | editor=von Bonin, G. | title=Some Papers on the Cerebral Cortex | year=1960 | publisher=Charles Thomas |location= Springfield IL | pages=73–96}}</ref> This confirmed experimentally the existence of a cortical motor center, which was inferred by Jackson a few years earlier on the basis of clinical observations.<ref>{{Cite book |last=Jackson |first=JH |title=Selected writings of John Hughlings Jackson |publisher=Hodder and Stoughton |year=1931}}</ref> Together with Broca's (1861)<ref>{{Cite journal |last=Broca |first=P |date=1861 |title=Sur le principe des localisations cérébrales |journal=Bulletin de la Société d'Anthropologie |volume=2 |pages=190–204}}</ref> discovery of a language center in the left hemisphere of the cerebral cortex, the demonstration of a cortical motor center put an end to Flourens' <ref>{{Cite book |last=Flourens |first=MJP |title=Recherches expérimentales sur les propriétés et les fonctions du systeme nerveux dans les animaux vertébrés |date=1842 |publisher=Crevot |location=Paris}}</ref> doctrine (1842) that function was widely distributed across the cerebral cortex (i.e., not localized).<ref>{{Cite journal |last=Capaday |first=Charles |date=2004 |title=The Integrated Nature of Motor Cortical Function |url=http://journals.sagepub.com/doi/10.1177/107385403262109 |journal=The Neuroscientist |language=en |volume=10 |issue=3 |pages=207–220 |doi=10.1177/107385403262109 |issn=1073-8584 |pmid=15155060 |s2cid=7174916}}</ref>

A little later, in 1874, [[David Ferrier]],<ref name=Ferrier>{{cite journal | author=[[David Ferrier|Ferrier, D]] | year=1874 | title=Experiments on the brain of monkeys - No. 1 | journal=Proc. R. Soc. Lond. | volume= 23 | pages=409–430 | doi=10.1098/rspl.1874.0058 | issue=156–163| s2cid=144533070 }}</ref> working in the laboratory of the [[Stanley Royd Hospital|West Riding Lunatic Asylum]] at [[Wakefield]] (at the invitation of its director, [[James Crichton-Browne]]), mapped the motor cortex in the monkey brain using electrical stimulation.  He found that the motor cortex contained a rough map of the body with the feet at the top (or dorsal part) of the brain and the face at the bottom (or ventral part) of the brain. He also found that when electrical stimulation was maintained for a longer time, such as for a second, instead of being discharged over a fraction of a second, then some coordinated, seemingly meaningful movements could be caused, instead of only muscle twitches.

After Ferrier's discovery, many neuroscientists used electrical stimulation to study the map of the motor cortex in many animals including monkeys, apes, and humans.<ref name=Campbell>{{cite book | author=Campbell, A. W. | year=1905 | title=Histological Studies on the Localization of Cerebral Function | location=Cambridge, MA | publisher=Cambridge University Press | oclc=6687137 | url=https://archive.org/details/histologicalstu00campgoog | url-status=live | archive-url=https://web.archive.org/web/20160602130611/https://archive.org/details/histologicalstu00campgoog | archive-date=2016-06-02 }}</ref><ref name=Vogt&Vogt>{{cite journal | author1-link=Cécile Vogt-Mugnier|last1=Vogt|first1=C.|last2=Vogt|first2=O.|author2-link=Oskar Vogt| year=1919 | title=Ergebnisse unserer Hirnforschung | journal=Journal für Psychologie und Neurologie | volume=25 | pages=277–462}}</ref><ref name=Foerster>{{cite journal | author=[[Otfrid Foerster|Foerster, O]] | year=1936 | title=The motor cortex of man in the light of Hughlings Jackson's doctrines | journal=Brain | volume=59 | pages=135–159 | doi=10.1093/brain/59.2.135 | issue=2}}</ref><ref name=Beevor&Horsley>{{cite journal | author=[[Charles Edward Beevor|Beevor, C.]] and [[Victor Horsley|Horsley, V]] | year=1887 | title=A minute analysis (experimental) of the various movements produced by stimulating in the monkey different regions of the cortical centre for the upper limb, as defined by Professor Ferrier | journal=Phil. Trans. R. Soc. Lond. B | volume=178 | pages=153–167 | doi=10.1098/rstb.1887.0006| doi-access=free }}</ref><ref name=Grunbaum&Sherrington>{{cite journal | author=Grunbaum A. and [[Charles Sherrington|Sherrington, C]] | year=1901 | title=Observations on the physiology of the cerebral cortex of some of the higher apes. (Preliminary communication) | journal=Proc. R. Soc. Lond. | volume=69 | pages=206–209 | doi=10.1098/rspl.1901.0100 | issue=451–458| bibcode=1901RSPS...69..206G | doi-access= | s2cid=145245312 }}</ref>

One of the first detailed maps of the human motor cortex was described in 1905 by Campbell.<ref name=Campbell/> He did autopsies on the brains of amputees. A person who had lost an arm would over time apparently lose some of the neuronal mass in the part of the motor cortex that normally controls the arm. Likewise, a person who had lost a leg would show degeneration in the leg part of motor cortex. In this way the motor map could be established. In the period between 1919 and 1936 others mapped the motor cortex in detail using electrical stimulation, including the husband and wife team [[Cécile Vogt-Mugnier|Vogt]] and [[Oskar Vogt|Vogt]],<ref name=Vogt&Vogt/> and the neurosurgeon [[Otfrid Foerster|Foerster]].<ref name=Foerster/>

Perhaps the best-known experiments on the human motor map were published by Penfield in 1937.<ref name=Penfield&Boldrey>{{cite journal | author1-link=Wilder Penfield|last1=Penfield|first1=W.|last2=Boldrey|first2=E. | year=1937 | title=Somatic motor and sensory representation in the cerebral cortex of man as studied by electrical stimulation | journal=Brain | volume=60 | pages=389–443 | doi=10.1093/brain/60.4.389 | issue=4}}</ref><ref name=Penfield>{{cite journal | author=[[Wilder Penfield|Penfield, W.]] | year=1959 | title=The interpretive cortex | journal=Science | volume=129 | pages=1719–1725 | pmid=13668523 | issue=3365|doi=10.1126/science.129.3365.1719 | bibcode=1959Sci...129.1719P | s2cid=37140763 }}</ref> Using a procedure that was common in the 1930s, he examined epileptic patients who were undergoing brain surgery. These patients were given a local anesthetic, their skulls were opened, and their brains exposed. Then, electrical stimulation was applied to the surface of the brain to map out the speech areas.  In this way, the surgeon would be able to avoid any damage to speech circuitry. The brain focus of the epilepsy could then be surgically removed. During this procedure, Penfield mapped the effect of electrical stimulation in all parts of the cerebral cortex, including motor cortex.

Penfield is sometimes mistakenly considered to be the motor cortex map discoverer. It was discovered approximately 70 years before his work. However, Penfield drew a picture of a human-like figure stretched over the cortical surface and used the term "homunculus" (diminutive of "homo", Latin for "man") to refer to it. It is perhaps for this reason that his work has become so popular in neuroscience. Penfield knew the homunculus idea was a caricature. He stated, '<nowiki/>''It is a cartoon of representation in which scientific accuracy is impossible''<nowiki/>'.<ref>{{Cite book |last=Penfield W and Rasmussen T |title=The cerebral cortex of man: a clinical study of localization of function |publisher=McMillan |year=1950 |location=New York}}</ref> Nearly fifty years before,<ref>{{Cite book |last=Sherrington |first=C.S. |title=The integrative action of the nervous system |publisher=Yale University Press |year=1947 |edition=2nd |location=New Haven}}</ref> Sherrington (1906) made the point more cogently stating '''The student looking over the political map map of a continent may little realise the complexity of the populations and states so simply represented. We looking at the brain chart of the text book may never forget the unspeakable complexity of the reactions thus rudely symbolised and spatially indicated''´. While pictures of an orderly representation of limb segments across the cortical surface (such as the one shown above) have endured in textbooks, they are erroneous and misleading.<ref>{{Cite journal |last1=Capaday |first1=Charles |last2=Ethier |first2=Christian |last3=Van Vreeswijk |first3=Carl |last4=Darling |first4=Warren G. |date=2013 |title=On the functional organization and operational principles of the motor cortex |journal=Frontiers in Neural Circuits |volume=7 |page=66 |doi=10.3389/fncir.2013.00066 |doi-access=free |issn=1662-5110 |pmc=3629310 |pmid=23616749}}</ref>

==The motor cortex map==
A simple view, that is almost certainly too limited and that dates back to the earliest work on the motor cortex, is that neurons in the motor cortex control movement by a [[Feed forward (control)|feed-forward]] direct pathway. In that view, a neuron in the motor cortex sends an [[axon]] or projection to the spinal cord and forms a [[synapse]] on a [[motor neuron]]. The motor neuron sends an electrical impulse to a muscle. When the neuron in the cortex becomes active, it causes a muscle contraction. The greater the activity in the motor cortex, the stronger the muscle force. Each point in the motor cortex controls a muscle or a small group of related muscles. This description is only partly correct.

Most neurons in the motor cortex that project to the spinal cord [[synapse]] on [[interneuron]] circuitry in the spinal cord, not directly onto [[motor neuron]]s.<ref name=Bortoff&Strick>{{cite journal |author1=Bortoff, G.A.  |author2=Strick, P.L.  | year=1993 | title=Corticospinal terminations in two new-world primates: further evidence that corticomotoneuronal connections provide part of the neural substrate for manual dexterity | journal=J. Neurosci. | volume=13 | pages=5105–5118 | pmid=7504721 | issue=12 | pmc=6576412 | doi=10.1523/JNEUROSCI.13-12-05105.1993 }}</ref> One suggestion is that the direct, cortico-motoneuronal projections are a specialization that allows for the fine control of the fingers.<ref name=Bortoff&Strick/><ref name=Heffner&Masterton>{{cite journal |author1=Heffner, R.  |author2=Masterton, B.  | year=1975 | title=Variation in form of the pyramidal tract and its relationship to digital dexterity | journal=Brain Behav. Evol. | volume=12 | pages=161–200 | doi=10.1159/000124401 | pmid=1212616 | issue=3}}</ref>

The view that each point in the motor cortex controls a muscle or a limited set of related muscles was debated over the entire history of research on the motor cortex, and was suggested in its strongest and most extreme form by Asanuma<ref name=Asanuma>{{cite journal | author=Asanuma, H. | year=1975 | title=Recent developments in the study of the columnar arrangement of neurons within the motor cortex | journal=Physiol. Rev. | volume=55 | pages=143–156 | pmid=806927 | issue=2 | doi=10.1152/physrev.1975.55.2.143}}</ref> on the basis of experiments in cats and monkeys using electrical stimulation. However, almost every other experiment to examine the map, including the classic work of [[David Ferrier|Ferrier]]<ref name=Ferrier/> and of Penfield<ref name=Penfield&Boldrey/> showed that each point in the motor cortex influences a range of muscles and joints. The map is greatly overlapping. The overlap in the map is generally greater in the premotor cortex and supplementary motor cortex, but even the map in the primary motor cortex controls muscles in an extensively overlapped manner. Many studies have demonstrated the overlapping representation of muscles in the motor cortex.<ref name=Cheney&Fetz>{{cite journal |author1=Cheney, P.D.  |author2=Fetz, E.E.  | year=1985 | title=Comparable patterns of muscle facilitation evoked by individual corticomotoneuronal (CM) cells and by single intracortical microstimuli in primates: evidence for functional groups of CM cells | journal=J. Neurophysiol. | volume=53 | pages=786–804 | pmid=2984354 | issue=3 | doi=10.1152/jn.1985.53.3.786}}</ref><ref name=Schieber&Hibbard>{{cite journal |author1=Schieber, M.H.  |author2=Hibbard, L.S.  | year=1993 | title=How somatotopic is the motor cortex hand area? | journal=Science | volume=261 | pages=489–492 | doi=10.1126/science.8332915 | pmid=8332915 | issue=5120|bibcode=1993Sci...261..489S }}</ref><ref name=Rathelot&Strick>{{cite journal |author1=Rathelot, J.A.  |author2=Strick, P.L.  | year=2006 | title=Muscle representation in the macaque motor cortex: an anatomical perspective | journal=Proc. Natl. Acad. Sci. U.S.A. | volume=103 | pages=8257–8262 | doi=10.1073/pnas.0602933103 | pmid=16702556 | issue=21 | pmc=1461407|bibcode=2006PNAS..103.8257R |doi-access=free }}</ref><ref name=Park&etal>{{cite journal | author=Park, M.C., Belhaj-Saif, A., Gordon, M. and Cheney, P.D. | year=2001 | title=Consistent features in the forelimb representation of primary motor cortex in rhesus macaques | journal=J. Neurosci. | volume=21 | pages=2784–2792 | pmid=11306630 | issue=8 | pmc=6762507 | doi=10.1523/JNEUROSCI.21-08-02784.2001 }}</ref><ref name=Sanes&etal>{{cite journal | author=Sanes, J.N., Donoghue, J.P., Thangaraj, V., Edelman, R.R. and Warach, S. | year=1995 | title=Shared neural substrates controlling hand movements in human motor cortex | journal=Science | volume=268 | pages=1775–1777 | doi=10.1126/science.7792606 | pmid=7792606 | issue=5218| bibcode=1995Sci...268.1775S }}</ref><ref name=Donoghue&etal>{{cite journal | author=Donoghue, J.P., Leibovic, S. and Sanes, J.N. | year=1992 | title=Organization of the forelimb area in squirrel monkey motor cortex: representation of digit, wrist and elbow muscles | journal=Exp. Brain Res. | volume=89 | issue=1 | pages=1–10 | doi=10.1007/bf00228996 | pmid=1601087| s2cid=1398462 }}</ref><ref name=Meier&etal>{{cite journal | author=Meier, J.D., Aflalo, T.N., Kastner, S. and [[Michael Graziano|Graziano, M.S.A.]] | year=2008 | title=Complex organization of human primary motor cortex: A high-resolution fMRI study | journal=J. Neurophysiol. | volume=100 | pages=1800–1812 | doi=10.1152/jn.90531.2008 | pmid=18684903 | issue=4 | pmc=2576195}}</ref><ref name=":1">{{Cite journal |last1=Schneider |first1=Cyril |last2=Zytnicki |first2=Daniel |last3=Capaday |first3=Charles |date=2001 |title=Quantitative evidence for multiple widespread representations of individual muscles in the cat motor cortex |url=https://linkinghub.elsevier.com/retrieve/pii/S030439400102105X |journal=Neuroscience Letters |language=en |volume=310 |issue=2–3 |pages=183–187 |doi=10.1016/S0304-3940(01)02105-X |pmid=11585597 |s2cid=26687967}}</ref> To be clear as to what the often used term 'overlapping map' actually means, it is better to state that muscles are represented many times over on the cortical surface in non-contiguous loci, intermingled with the representation of other muscles acting at the same, or at a different, joint.<ref name=":1" />

It is believed that as an animal learns a complex movement repertoire, the motor cortex gradually comes to coordinate among muscles.<ref name=Nudo&etal>{{cite journal | author=Nudo, R.J., Milliken, G.W., Jenkins, W.M. and Merzenich, M.M. | year=1996 | title=Use-dependent alterations of movement representations in primary motor cortex of adult squirrel monkeys | journal=J. Neurosci. | volume=16 | pages=785–807 | pmid=8551360 | issue=2 | doi=10.1523/JNEUROSCI.16-02-00785.1996 | pmc=6578638}}</ref><ref name=Martin&etal>{{cite journal | author=Martin, J.H., Engber, D. and Meng, Z. | year=2005 | title=Effect of forelimb use on postnatal development of the forelimb motor representation in primary motor cortex of the cat | journal=J. Neurophysiol. | volume=93 | pages=2822–2831 | doi=10.1152/jn.01060.2004 | pmid=15574795 | issue=5}}</ref>

[[File:Human motor map.jpg|thumb|right|Map of the body in the human brain.]]

The clearest example of the coordination of muscles into complex movement in the motor cortex comes from the work of [[Michael Graziano|Graziano]] and colleagues on the monkey brain.<ref name=Graziano&2008>{{cite book | author=[[Michael Graziano|Graziano, M.S.A.]] | year=2008 | title=The Intelligent Movement Machine | publisher=Oxford University Press | location=Oxford, UK}}</ref><ref name=Graziano&Taylor&Moore/> They used electrical stimulation on a behavioral time scale, such as for half a second instead of the more typical hundredth of a second. They found that this type of stimulation of the monkey motor cortex often evoked complex, meaningful actions. For example, stimulation of one site in the cortex would cause the hand to close, move to the mouth, and the mouth to open. Stimulation of another site would cause the hand to open, rotate until the grip faced outward, and the arm to project out as if the animal were reaching. Different complex movements were evoked from different sites and these movements were mapped in the same orderly manner in all monkeys tested. Computational models<ref name=Graziano&Aflalo2007>{{cite journal | author=[[Michael Graziano|Graziano, M.S.A.]] and Aflalo, T.N. | year=2007 | title=Mapping behavioral repertoire onto the cortex | journal=Neuron | volume=56 | pages=239–251 | doi=10.1016/j.neuron.2007.09.013 | pmid=17964243 | issue=2| doi-access=free }}</ref> showed that the normal movement repertoire of a monkey, if arranged on a sheet such that similar movements are placed near each other, will result in a map that matches the actual map found in the monkey motor cortex. This work suggests that the motor cortex does not truly contain a homunculus-type map of the body. Instead, the deeper principle may be a rendering of the movement repertoire onto the cortical surface. To the extent that the movement repertoire breaks down partly into the actions of separate body parts, the map contains a rough and overlapping body arrangement noted by researchers over the past century.

A similar organization by typical movement repertoire has been reported in the posterior parietal cortex of monkeys and [[galagos]]<ref name=Stepniewska&etal>{{cite journal | author=Stepniewska, I., Fang, P.C. and Kaas, J.H. | year=2005 | title=Microstimulation reveals specialized subregions for different complex movements in posterior parietal cortex of prosimian galagos | journal=Proc. Natl. Acad. Sci. U.S.A. | volume=102 | pages=4878–4883 | doi=10.1073/pnas.0501048102 | pmid=15772167 | issue=13 | pmc=555725| bibcode=2005PNAS..102.4878S | doi-access=free }}</ref><ref name=Gharbawie&etal>{{cite journal | author=Gharbawie, O.A., Stepniewska, I., Qi, H. and Kaas, J.H. | year=2011 | title=Multiple parietal-frontal pathways mediate grasping in macaque monkeys | journal=J. Neurosci. | volume=31 | pages=11660–11677 | doi=10.1523/JNEUROSCI.1777-11.2011 | pmid=21832196 | issue=32 | pmc=3166522}}</ref> and in the motor cortex of rats<ref name=Haiss&Schwartz>{{cite journal |author1=Haiss, F.  |author2=Schwarz, C  | year=2005 | title=Spatial segregation of different modes of movement control in the whisker representation of rat primary motor cortex | journal=J. Neurosci. | volume=25 | pages=1579–1587 | doi=10.1523/JNEUROSCI.3760-04.2005 | pmid=15703412 | issue=6 | pmc=6726007}}</ref><ref name=Ramanathan&etal>{{cite journal | author=Ramanathan, D., Conner, J.M. and Tuszynski, M.H. | year=2006 | title=A form of motor cortical plasticity that correlates with recovery of function after brain injury | journal=Proc. Natl. Acad. Sci. U.S.A. | volume=103 | pages=11370–11375 | doi=10.1073/pnas.0601065103 | pmid=16837575 | issue=30 | pmc=1544093| bibcode=2006PNAS..10311370R | doi-access=free }}</ref> and mice.<ref>{{Cite journal|title = Distinct Cortical Circuit Mechanisms for Complex Forelimb Movement and Motor Map Topography|journal = Neuron|issn = 0896-6273|pmid = 22542191|pages = 397–409|volume = 74|issue = 2|doi = 10.1016/j.neuron.2012.02.028|first1 = Thomas C.|last1 = Harrison|first2 = Oliver G. S.|last2 = Ayling|first3 = Timothy H.|last3 = Murphy|year=2012|doi-access = free}}</ref> Notwithstanding, direct tests of the idea that the motor cortex contains a movement repertoire have not corroborated this hypothesis.<ref name=":0">{{Cite journal |last=Capaday |first=Charles |date=2022 |title=Motor cortex outputs evoked by long-duration microstimulation encode synergistic muscle activation patterns not controlled movement trajectories |journal=Frontiers in Computational Neuroscience |volume=16 |doi=10.3389/fncom.2022.851485 |issn=1662-5188 |pmc=9434634 |pmid=36062251 |doi-access=free}}{{Creative Commons text attribution notice|cc=by4|from this source=yes}}</ref> Varying the initial position of the forelimb does not change the muscle synergies evoked by microstimulation of a motor cortical point. Consequently, the evoked movements reach nearly the same final end point and posture, with variability. However, the movement trajectories are quite different depending on the initial limb posture and the starting position of the paw. The evoked movement trajectory is most natural when the forelimb lays pendant ~ perpendicular to the ground (i.e., in equilibrium with the gravitational force). From other starting positions, the movements do not appear natural. The paths of the paw are curved with changes and reversals of direction and the passive influence of the gravitational force on the movements is obvious. These observations demonstrate that while the output of the cortical point evokes a seemingly coordinated limb movement from a rest position, it does not specify a particular movement direction or a controlled trajectory from other initial positions. Thus, in natural conditions a controlled movement must depend on the coordinated activation of a multitude of cortical points, terminating at a final locus of motor cortical activity, which holds the limb at a spatial location.<ref name=":0" /> These findings are inconsistent with the idea of the representation of the movement repertoire on the cortical surface.

==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).

==See also==
* [[Cortical homunculus]]
* [[Motor skill]]

==References==
{{reflist|30em}}

==Further reading==
* Canavero S. Textbook of therapeutic cortical stimulation. New York: Nova Science, 2009

==External links==
* [http://nba.uth.tmc.edu/neuroscience/s3/chapter03.html Motor Cortex]

{{commons category}}
{{Cerebral cortex}}

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[[Category:Cerebral cortex]]
[[Category:Motor system]]