A single motor unit recording technique for studying the differential activation of corticospinal volleys by transcranial magnetic stimulation

The purpose of this method is to establish a single motor unit recording technique to study the differential activation of corticospinal volleys by various types of transcranial magnetic stimulation (TMS). TMS is performed with various coil orientations over the hand or leg motor areas and surface EMG, and single motor unit recordings are made either from the studied hand or leg muscle. Transcranial electrical stimulation (TES) is also performed over the motor cortex as well as at the foramen magnum level to determine the latency of D waves. The intensity of stimulation is set just above the motor threshold for each type of stimulation. This method makes it possible to activate some I volleys (especially I1 and I3 waves) preferentially, if not selectively, from the hand and leg motor areas. The obtained results accord well with recent epidural recording studies, which lends support to the validity of this method.