Evaluation of conduction in central motor pathways: techniques, pathophysiology, and clinical interpretation

This communication summarizes the highlights of this symposium and reviews our current understanding of the clinical neurophysiology of conduction in central motor pathways produced by transcranial or direct brain stimulation. Direct (D wave) and indirect (I wave) volleys of descending impulses in the pyramidal system result from motor cortex stimulation and determine the measured responses. The advantages and disadvantages of the electrical and the magnetic stimulating modalities are assessed. The increased latency produced by magnetic as opposed to electrical stimulation is considered. Present clinical applications are discussed. The safety record is encouraging, but has aspects that must be addressed. Potential problems of the interpretation of motor evoked potentials in patients with central nervous system disease are emphasized in light of the pathophysiological mechanism underlying these potentials.