The motor and premotor function. Primary motor cortex (somatic motor area) are located in precentral gyrus. This region includes the giant pyramidal cells of Betz in layer V; at this site the gray matter is of maximum thickness. The motor area gives rise to impulses that initiate volitional movements on the opposite side of the body. It is subdivided into centers; each of these preferentially controls muscles that govern movements of individual parts of the opposite half of the body. It is somatotopically organized. These are represented in inverted order. Destruction of this area caused paresis or paralysis of the opposite side of the body. This paralysis affects predominantly the distal portions of the extremities, and fine, skilled volitional movements are entirely abolished. Because the larynx, pharynx, palate, trunk muscles, diaphragm, rectum, and bladder are bilaterally innervated, the functions of these structures are little affected with unilateral lesions. The premotor locates anteriorly of the precentral gyrus and effects opposite half of the body motor control. It is involved in the planning of movements. Irritation of the motor (and/or pre-motor) cortex causes focal or jacksonian convulsions.
The frontal motor eye field. Lies anterior to the premotor cortex and controls voluntary movement of the eyes, especially when moving eyes to follow a moving target. Stimulation of this region results in strong, rapid conjugate deviation of the eyes to the opposite side, which may be accompanied by conjugate movement of the head and rotation of the trunk. Destruction of this area is followed by paresis of conjugate gaze to the opposite side.
The motor speech areas. The lower portion of the motor and premotor region is known as Broca's area, or the motor speech area. Destructive lesions of this region produce an oral expressive type of aphasia.
Destruction of the anterior two-thirds of the frontal lobe convexity results in deficits in the following functions: concentration, orientation, abstracting ability, loss of initiative, inappropriative behavior, release of grasping reflexes, gait apraxia and sphicteric incontinenced.