ORIGIN OF P16 MEDIAN NERVE SEP COMPONENT IDENTIFIED BY DIPOLE SOURCE ANALYSIS - SUBTHALAMIC OR WITHIN THE THALAMOCORTICAL RADIATION

Following median nerve stimulation, several monophasic peaks were reco rded at the scalp in the 15-18 ms time range. Source analysis, using t hree different methods, modelled a source near the centre of the head with an orientation towards the activated hemisphere and a peak activi ty at 16 ms post stimulus. Magnetic recordings detected no signal in t his time range, which confirmed a subcortical location of the source. From dipole localization it was not possible to assign the exact origi n of the P16 source to either the subthalamic level or the thalamo-cor tical radiation, because of the limited spatial resolution at the cent re of the spherical head model. An estimate of the conduction velocity of the medial lemniscus pointed towards a subthalamic origin. The P16 source was preserved in two patients with a lesion of the thalamo-cor tical radiation and the ventral thalamus. Further evidence for a subth alamic location of P16 was derived from the physical mechanisms genera ting far-field potentials.