The clearest example of the coordination of muscles into complex movement in the motor cortex comes from the work of Graziano and colleagues on the monkey brain.
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In neurophysiological studies, the motor system is modeled as a distributed, often hierarchical system with the spinal cord controlling the "most automatic" of movements such as stretch reflexes, and the cortex controlling the "most voluntary" actions such as reaching for an object, with the brainstem performing a function somewhere in between the two.
The stimulation of the surface of the cerebral cortex by using brain stimulation was used to investigate the motor cortex in animals by researchers such as Eduard Hitzig (1838–1907), Gustav Fritsch (1838–1927), David Ferrier (1842–1928) and Friedrich Goltz (1834–1902).
For example, in TMS studies it has been shown that during stimulation of parts of the motor cortex that are active during leg motions comprehension of sentences describing activities dealing with legs is improved.
Graziano and colleagues suggested an alternative principle of organization for the primary motor cortex and the caudal part of the premotor cortex, all regions that project directly to the spinal cord and that were included in the Penfield and Woolsey definition of M1.
or so-called readiness potentials which reflect the degree of motor activation in the brain's motor cortex and can be measured by electro-encephalographic methods.
The locomotion hypothesis is an example of interpreting the motor cortex in terms of the underlying behavioral repertoire from which abstract control functions emerge, an approach emphasized by Graziano and colleagues.