Editing Motor cortex (section)

==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.