Movement-related cortical potentials.

Movement-related cortical potentials represent averaged electroencephalographic activity before and after a voluntary movement. They begin with a slowly rising negativity, called the Bereitschaftspotential (BP), and progress to a steeper, later negativity starting about 400 msec before the onset of movement, called the negativity slope (NS'). They are followed by the motor potential, which is seen partly before and partly after the movement. The initial slope of motor potential (isMP) occurs just before the onset of electromyographic (EMG) activity, is focal topographically over the primary motor cortex, and probably represents activation of the primary motor cortex. This contralateral focal negativity persists for 30 to 50 msec after the onset of EMG activity, when it then drops off in the central and parietal regions, an event called the parietal peak of motor potential (ppMP). Subsequently, the peak negativity shifts toward the anterior contralateral area, where it reaches the highest negativity of the recording, called the frontal peak of motor potential (fpMP). The fpMP appears to represent feedback from the movement and may originate, in part, from the supplementary motor area. In patients with congenital mirror movements, the isMP occurs bilaterally. In patients with Parkinson's disease and cerebellar disease, the isMP is more diffuse and the fpMP is more posterior than normal. Movement-related cortical potentials are useful research tools, but are not yet appropriate for clinical applications.