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Motor cortex

The motor cortex is the region of the cerebral cortex involved in the planning, 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.

Motor cortex

The 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.

posterior parietal cortex

The , 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.

primary somatosensory cortex

History[edit]

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.[43] 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.[44] Together with Broca's (1861)[45] 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' [46] doctrine (1842) that function was widely distributed across the cerebral cortex (i.e., not localized).[47]


A little later, in 1874, David Ferrier,[48] working in the laboratory of the 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.[1][4][5][49][50]


One of the first detailed maps of the human motor cortex was described in 1905 by Campbell.[1] 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 Vogt and Vogt,[4] and the neurosurgeon Foerster.[5]


Perhaps the best-known experiments on the human motor map were published by Penfield in 1937.[7][8] 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 discoverer of the map in motor cortex. 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. It should be noted, however, that Penfield knew well that the idea of a homunculus was a caricature. He stated, 'It is a cartoon of representation in which scientific accuracy is impossible'.[51] Nearly fifty years before,[52] 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´. It is therefore important to realize that 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.[53]

Cortical homunculus

Motor skill

Canavero S. Textbook of therapeutic cortical stimulation. New York: Nova Science, 2009

Motor Cortex