Ankle Toes The premotor area, also shown in Figure 1, lies 1 to 3 centimeters anterior to the primary motor cortex. It extends inferiorly into the sylvian fissure and superiorly into the longitudinal fissure, where it abuts the supplementary motor area, which has functions similar to those of the premotor area. The topographical organization of the premotor cortex is roughly the same as that of the primary motor cortex, with the mouth and face areas located most laterally; as one moves upward, the hand, arm, trunk, and leg areas are encountered.
Fig1. Motor and somatosensory functional areas of the cerebral cortex. The numbers 4, 5, 6, and 7 are Brodmann’s cortical areas, as explained in Chapter 48.
Nerve signals generated in the premotor area cause much more complex “patterns” of movement than the discrete patterns generated in the primary motor cortex. For instance, the pattern may be to position the shoulders and arms so that the hands are properly oriented to perform specific tasks. To achieve these results, the most anterior part of the premotor area first develops a “motor image” of the total muscle movement that is to be per formed. Then, in the posterior premotor cortex, this image excites each successive pattern of muscle activity required to achieve the image. This posterior part of the premotor cortex sends its signals either directly to the primary motor cortex to excite specific muscles or, often, by way of the basal ganglia and thalamus back to the primary motor cortex.
A special class of neurons called mirror neurons becomes active when a person performs a specific motor task or when he or she observes the same task performed by others. Thus, the activity of these neurons “mirrors” the behavior of another person as though the observer was performing the specific motor task. Brain imaging studies indicate that these neurons transform sensory representations of acts that are heard or seen into motor representations of these acts. Many neurophysiologists believe that these mirror neurons may be important for understanding the actions of other people and for learning new skills by imitation. Thus, the premotor cortex, basal ganglia, thalamus, and primary motor cortex constitute a complex overall system for the control of complex patterns of coordinated muscle activity.
