Motor cortex excitability during ballistic forearm and finger movements.

In a ballistic forearm flexion movement, a centrally programmed triphasic pattern of electromyogram (EMG) is seen with two bursts in biceps and a single burst in triceps. Rapid abduction of the index finger, in contrast, is achieved with a single agonist burst. Transcranial magnetic and electrical stimuli, triggered at the onset of the EMG burst, have been used to probe cortical and spinal cord excitability during and after self-paced ballistic finger and forearm movements. The first phase is coincident with the initial agonist burst. The second phase in biceps is associated with the second agonist burst, but in the finger movement, the raised motor cortical excitability is not associated with any EMG. It is argued that the motor program for the two movements may be similar, despite there being large differences in the EMG pattern generated.