to grasp. PMDr(F7) PMDr may participate in learning to associate arbitrary sensory stimuli with specific movements or learning arbitrary response rules. In this sense it may resemble the prefrontal cortex more than other motor cortex fields. It may also have some relation to eye movement. Electrical stimulation in the PMDr can evoke eye movements and neuronal activity in the PMDr can be modulated by eye movement. PMVc(F4) PMVc or F4 is often studied with respect to its role in the sensory guidance of movement. Neurons here are responsive to tactile stimuli, visual stimuli, and auditory stimuli. These neurons are especially sensitive to objects in the space immediately surrounding the body, in so-called peripersonal space. Electrical stimulation of these neurons causes an apparent defensive movement as if protecting the body surface. This premotor region may be part of a larger circuit for maintaining a margin of safety around the body and guiding movement with respect to nearby objects. PMVr(F5) PMVr or F5 is often studied with respect to its role in shaping the hand during grasping and in interactions between the hand and the mouth. Electrical stimulation of at least some parts of F5, when the stimulation is applied on a behavioral time scale, evokes a complex movement in which the hand moves to the mouth, closes in a grip, orients such that the grip faces the mouth, the neck turns to align the mouth to the hand, and the mouth opens. Mirror neurons were first discovered in area F5 in the monkey brain by Rizzolatti and colleagues. These neurons are active when the monkey grasps an object. Yet the same neurons become active when the monkey watches an experimenter grasp an object in the same way. The neurons are therefore both sensory and motor. Mirror neurons are proposed to be a basis for understanding the actions of others by internally imitating the actions using one's own motor control circuits. History In the earliest work on the motor cortex, researchers recognized only one cortical field involved in motor control. Campbell in 1905 was the first to suggest that there might be two fields, a "primary" motor cortex and an "intermediate precentral" motor cortex. His reasons were largely based on cytoarchitectonics. The primary motor cortex contains cells with giant cell bodies known as "Betz cells". The Betz cells are rare or absent in the adjacent cortex. On similar criteria Brodmann in 1909