MOTOR CORTEX EXCITABILITY DURING BALLISTIC FOREARM AND FINGER MOVEMENTS

In a ballistic forearm flexion movement, a centrally programmed tripha sic 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 magne tic and electrical stimuli, triggered at the onset of the EMG burst, h ave been used to probe cortical and spinal cord excitability during an d after self-paced ballistic finger and forearm movements. in both, th e motor cortex has two phases of increased excitability. The first pha se is coincident with the initial agonist burst. The second phase in b iceps is associated with the second agonist burst, but in the finger m ovement, the raised motor cortical excitability is not associated with any EMG. It is argued that the motor program for the two movements ma y be similar, despite there being large differences in the EMG pattern generated. (C) 1996 John Wiley & Sons, Inc.