Thalamic potentials evoked by motor point stimulation

We studied thalamic potentials elicited by stimulation of the extensor digi torum communis muscle motor point during stereotactic surgery for movement disorders, in 6 patients with Parkinson's disease and 1 with cerebral palsy , muscle afferent-evoked thalamic potentials (METPs) were recorded in the v entral intermediate (Vim) nucleus. METPs consisted of three peaks with an a verage latency of 11.02 +/- 0.80 ms for initial positive peak (PI), 13.04 /- 0.58 ms for negative (N), and 14.30 +/- 0.87 ms for later positive peak (PII). These METPs were different from those evoked by median nerve stimula tion, No peaks corresponding to the N20 component of the somatosensory evok ed potential were recorded from C3 or C4 scalp electrodes. The METP amplitu des in the ventrolateral (VL) nucleus were markedly lower than those in the Vim nucleus. These findings suggest that METPs in the Vim nucleus are resp onses that occur via the fast conducting group la afferent fibers rather th an somatosensory afferent fibers. (C) 2000 John Wiley & Sons, Inc.