In the human brain, the premotor cortex consists of interconnected areas within the primary motor cortex, which is located in the frontal lobe of the brain. The word “motor” refers to function of the areas, which is to send messages that direct movements of the body to accomplish specific tasks. The premotor cortex has a lateral and medial area. Each of the two areas is connected by neural pathways, which function like a series of electrical wires, to the primary motor cortex. The lateral area directs physical movement in response to external stimulus, while the medial area responds to internal stimulus from the brain itself and relays the intent to perform a particular physical act.
Neurons are the basic structural units of the nervous system. The majority of the neurons in the lateral area are thought to be linked to the occurrence of motor functions such as grasping an object. Research involving monkeys has generally supported this conclusion. When monkeys were trained to reach in different directions following a visual cue, the neurons in the lateral area began to “fire,” or transmit information, more rapidly in the time between the cue and the physical act of reaching. This indicated that the physical movement was in response to the external stimulus of the cue.
The medial area of the premotor cortex is also involved with body movement and motor skills. This area, however, is thought to operate on internal instead of external stimulus. Researchers point to the fact that monkeys with the medial area removed show a marked reduction in the amount of physical movements initiated by the monkeys themselves. At the same time, physical movement in response to external cues stayed the same. This indicated that the stored information in the medial area relies on its own encoding to perform specific movements.
Imaging studies suggest that the medial area functions much the same way in humans. The medial area activates when test subjects perform motor tasks from memory. This is true even in the absence of any visual cues or written or verbal instructions.
Studies of the human brain also support the connection between the motor cortex and physical movement. Patients with damage to the frontal lobe have difficulty learning to select a specified movement based on visual cues. This difficulty arises even when the patient understands the instructions and eventually performs the correct movement. Individuals with premotor cortex lesions may also show difficulty in following visual or verbal commands to perform a movement prompted externally.
