M1, F1, MC, Area 4, precentral cortex
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Short Answer: A lot!
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M1 has a large number of pyramidal tract neurons (PTNs). These neurons discharge in relation to the force applied in a wrist flexion/extension task, but do not respond much to the direction of displacement. (Evarts, '68) Small diameter PTNs are the majority of M1 efferents (see connections) and receive continuous feedback during postures as well as during movement. (Fromm, Wise, Evarts '84) M1 has classically been thought to have very strong somatotopic organization, but recently within limb somatotopy has been challenged. (Schieber, 2001) Both sensory and motor stimuli evoke M1 responses, including both passive and active motions. (Fetz et. al. '80) M1 responds significantly to isometric force and inertial load tasks. (Kalaska) Later studies (Georgopoulis) looked at direction tuning and population vectors, and implied that M1 was an encoding force - it did not fit the population vector model. Directional tuning in M1 was found to increase from stimulus (25%) to set (61%) to movement (86%). (Crutcher and Shen) The majority of corticomotoneuronal (CM) cells produce post spike effects in 2 or more muscles. Crutcher and Alexander ('90) recorded from a number of cells in M1. They found that during the preparatory phase of movement, 37% of cells showed task related discharge, but only 11% of cells showed this discharge only during the preparatory phase. In most cases this was independent of the loading activity. |
Classic Penfield Homunculus showing somatotopic organization of M1 |
Unsurprisingly, M1 connects to many, many other areas. Afferents come from other motor areas, the hypothalamus, the thalamus, and beyond. Efferents go to some of the same areas, and also go down important spinal pathways. Table from Leichnetz '86.
M1 Connections - The long version
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Afferents TO Primary Motor Cortex |
Efferents FROM Primary Motor Cortex |
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Supplemental motor area (SMA) (area 6) Postcentral gyrus (areas 2, 1 a.k.a. SI) Superior parietal lobule (PE/PEa) Inferior parietal lobule (PF, PFop) Cingulate cortex (dorsal LA)
Claustrum (dorsal)
Nucleus diagonal band of Broca Nucleus basalis of Meynert
Lateral hypothalamus
Ventral lateral nucleus (Vlo, Vlc) Ventral posterolateral nucleus (VPLo) Mediodorsal nucleus Intralaminar complex: Central lateral nucleus Centromedian nucleus
Dorsal raphe nucleus Superior central nucleus Locus ceruleus and subceruleus |
Supplemental motor area (SMA) (area 6) Postcentral gyrus (areas 2, 1 a.k.a. SI) Superior parietal lobule (PE/PEa) Inferior parietal lobule (PF, PFop) Cingulate cortex (dorsal LA)
Claustrum (dorsal) Putamen
Nucleus reticularis thalami Subthalamic nucleus Prerubral field
Ventral lateral nucleus (Vlo, Vlc) Ventral posterolateral nucleus (VPLo) Mediodorsal nucleus Intralaminar complex: Central lateral nucleus Centromedian nucleus
Nucleus of Darkschewitsch Parvicellular red nucleus (VL) Magnocellular red nucleus Nucleus of the posterior commissure
Pontine reticular formation Nucleus reticularis tegmenti pontis (lateral) Basilar pontine gray (peduncular) Medullary reticular formation Lateral reitcular nucleus |
Yes, in fact, we do have an M1. It's very important for humans too.
There appears to be a body map of some sort in our M1. Lotze et. al. 2000 found adjacent lip and tongue representation.
A task modulated coherence has been found between M1 and hand EMG. (Lomon, 2000)
In a hand - based task, disruption of ipsilateral motor cortex was found to cause timing errors, disruption of contralateral motor cortex was found to cause accuracy errors. (Chen, 1997)
There is reorganization of activity in M1 with practice, suggesting slowly evolving, long-term, experience-dependent reorganization of the adult M1. This could underlie the acquisition and retention of the motor skill. (Korni et. al. 1995)