DIFFERENTIAL VOLUNTARY PROGRAMMING OF FINGERS EXTENSOR COMMANDS REVEALED BY NONINVASIVE TRANSCRANIAL MAGNETIC STIMULATION OF THE HUMAN BRAIN

Slightly suprathreshold magnetic stimuli were delivered over the left scalp while a normal human subject attended a sensory signal which cal led for a motor response of right fingers in a reaction time paradigm. The cortico-motoneuronal systems of the two muscles producing finger extension disclosed a remarkable physiological differentiation. Brain magnetic stimulation delivered just before the subject's motor respons e revealed cortico-motoneuronal facilitation for one extensor muscle a nd concomitant inhibition for the other, depending on the verbal instr uctions that had been given to the subject before the experimental tri al. Thus, during the planning of specific finger manipulatory activiti es, the motor brain systems can achieve significant contrast in the me mbrane excitatory states of the motor cortical pyramidal neurones, eve n for synergic muscles.