Premotor cortex

Infobox Brain
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Caption = Image of brain with Brodmann areas numbered


Caption2 = Brodmann area 6
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BrainInfoType = ancil
BrainInfoNumber = 44
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DorlandsSuf= The premotor cortex is an area of motor cortex in the frontal lobe of the brain. It extends 3mm in front of the Primary motor cortex near the Sylvian fissure before narrowing to approximately 1mm near the Medial longitudinal fissure, where it has the prefrontal cortex. It is responsible for sensory guidance of movement and control of proximal and trunk muscles of the body, and is more or less equivalent with Brodmann area 6.

Anatomy and structure

The premotor cortex is dysgranular (a transition between the agranular motor cortex and the granular eulaminate frontal cortex), which means that there is only a faint granular lamina IV. This correspond to the Brodmann area 6 and the Vogts (), except for the part located on the medial surface of the hemisphere that has been later recognised as the accessory motor cortex (supplementary motor area - SMA). It is recommended to avoid number that have no topographical indication. As for all other parts of the cortex, there are several cultural schools concerning the conception and naming of cortical parts. For von Economo and followers, the premotor cortex is FB. Matelli more recently proposed still another system. The lateral component is a place that phylogenetically evolved considerably, for instance from cercopithecidae (like macaques) to man through apes. In macaque it is accepted that there are a dorsal premotor cortex (Pmd) and a ventral one (Pmv). The boundary between the two is admitted to be a horizontal line starting from the angle of the arcuate sulcus. In apes, there is no more arcuate sulcus and the appearance of a discontinuous irregular precentral sulcus. This is also the case in the human brain .

The precise taxonomic placement of the premotor cortex may differ between authors: The distinction made by Bailey and von Bonin of a central (perirolandic) region places the premotor cortex in this central region, thus posteriorly to the proper frontal cortex.

Afferents

ubcortical

Cortical

Through "U fibers" (short cortico-cortical axons) the premotor cortex receives many axons from the motor cortex in an horizontal manner respecting the somatotopic map of the motor cortex.

Efferents

ubcortical

Cortico-spinal

The axons of the premotor cortex contribute to the pyramidal bundle

triatum

Axons of the Vth layer contribute to the corticostriate connection ; a massive connection involving almost all parts of the cortex

Thalamus

The premotor cortex cortex sends axons to the motor thalamus. This (see thalamus) comprises a part receiving cerebellar axons (nucleus Ventralis Intermedius Vim or VL), a part receiving pallidal axons (nucleus Ventralis oralis VO) and a part receiving nigral axons (nucleus Ventralis anterio VA). The Vim is separated into two parts one ventrolateral and one mediodorsal VImM. The premotor cortex sends axons electively to VImM and VO

Central complex

ubthalamic nucleus

Cortical

Physiology

Mirror neurons are cells located in the premotor cortex, the part of the brain relevant to the planning, selection and execution of actions. It is a part of the Cerebral cortex.

References

*Bucy, P.C. (ed)(1949) The precentral motor cortex. 2d ed. Univ. Illinois Press Urbana
*Rizzolati, G., Luppino, G. and Matelli, M. (1998) The organization of the cortical motor system: new concepts. EEG Clin. Neurophysiol. 106:283-296
*von Bonin, G. (1949) Architecture of the precentral motor cortex and some adjacent areas. in Bucy, P.C. (ed)(1949) The precentral motor cortex. 2d ed. Univ. Illinois Press Urbana. pp.7-82