Interruption of a relay of corticospinal excitation by a spinal lesion at C6-C7

In a patient with a limited lesion of the spinal cord at the C6-C7 junction , ulnar and superficial radial-induced modulations of the motor evoked pote ntials (MEP) and of ongoing electromyographic (EMG) activity were observed in the biceps (above the lesion) but not in the triceps (below the lesion). This suggests an interruption of the axons of cervical propriospinal neuro ns. This relay transmits an indirect (disynaptic) component of corticospina l excitation to human upper limb motoneurons. Changes in it might be involv ed in compensatory mechanisms following central motor disorders. (C) 2001 J ohn Wiley & Sons, Inc.