Magnetic stimulation-induced modulations of motor unit firings extracted from multi-channel surface EMG

The noninvasive assessment of motor unit (MU) firing patterns on the basis of topographical information from 128-channel high-density surface electrom yography (SEMG) is reported. First, multi-channel MU action potential (MUAP ) templates are obtained by clustering detected firing events according to the surface topography of the MUAP. Second, a template-matching algorithm i s used to find all firings of a MU, including the superimpositions of MUAPs . From a single recording, the firing pattern of up to five MUs could be de rived. The modulation of MU firing by transcranial magnetic stimulation was analyzed in peri-stimulus time histograms, The results are similar to prev ious results of transcranial magnetic stimulation (TMS) obtained by needle electromyographic (EMG) recordings. The method can be used to investigate M U firing patterns in patients with central motor disorders. An additional a dvantage of the technique, apart from its noninvasiveness, is the structura l and functional information that it provides on the MUs, which is not obta ined by needle EMG. (C) 2000 John Wiley & Sons, Inc.