Participation of primary motor cortex in the programming of muscle activity during catching of a falling object

A sitting person has been exposed to transcranial magnetic stimulation (TMS) of the primary motor cortex shortly before and during increasing anticipatory grip force, while an object was falling into a cup held between the thumb and index finger of the subject. Comparison of the changes in the electrical activity of adductor pollicis brevis and the first dorsal interosseous muscles and of TMS response in these muscles revealed, on the one hand, a strong increase in TMS response not long before enhancement of muscle activity and, on the other hand, an insignificant increase in the response amplitude during substantial increase in muscle activity. An increase in the TMS response prior to initiation of motor activity suggests that the excitability of the primary motor cortex is enhanced due to specific processes caused by the direct involvement of the cortex in the programming of motor activity.