Brodmann area 4
Brodmann area 4 refers to the primary motor cortex of the human brain, one of the Brodmann areas. It is located in the posterior portion of the frontal lobe.
Brodmann area 4 is part of the precentral gyrus. The borders of this area are: the precentral sulcus in front, the medial [longitudinal fissure] at the top, the central sulcus in back, and the lateral sulcus along the bottom.
This area of cortex, as shown by Wilder Penfield and others, has the pattern of a homunculus. That is, the legs and trunk fold over the midline; the arms and hands are along the middle of the area shown here; and the face is near the bottom of the figure. Because Brodmann area 4 is in the same general location as primary motor cortex, the homunculus here is called the motor homunculus.
The term area 4 of Brodmann-1909 refers to a cytoarchitecturally defined portion of the frontal lobe of the guenon. It is located predominantly in the precentral gyrus. Brodmann-1909 regarded it as topographically and cytoarchitecturally homologous to the human gigantopyramidal area 4 and noted that it occupies a much greater fraction of the frontal lobe in the monkey than in the human.
Distinctive features : the cortex is unusually thick; the layers are not distinct; the cells are relatively sparsely distributed; giant pyramidal (Betz) cells are present in the internal pyramidal layer ; lack of an internal granular layer such that the boundary between the external pyramidal layer and the internal pyramidal layer is indistinct; lack of a distinct External [granular layer (cerebral cortex)|external granular layer] ; a gradual transition from the multiform layer to the subcortical white matter.