Topographical Distribution of the Evoked Potentials on Thalamic Ventrolateral and Dorsolateral Nuclei Stimulation

The purpose of the present study was to detect the existence of the different topographical distribution of the evoked potentials of the scalp EEG driven by the stimulation of the Ventro-lateral and Dorso-lateral nuclei of the thalamus respectively. Data were obtained from ten patients of Parkinsonism and other involuntary movement disorders. Stimulation electrodes were bipolar, with interelectrode distance of 1 to 2 mm, 0.1 to 1.0 mm in diameter. Stimulations of 0.05 to 1.0 msec, 10 to 50 V and 2 to 2.5 cps were applied. The evoked potentials were recorded from 24 to 48 needle electrodes inserted in the whole scalp with the indifferent electrode on the nose. Scalp electrodes were led to the ink-writing electroencephalogram, connected to the data recorder. The computer of average transients was used for analysis. Spacio-temporal maps were drawn. 1) Stimulation of either VL or DL produced the clear evoked potentials; the distribution of the maximal amplitude of the first negative-positive wave corresponds to the precentral motor cortex on the ipsilateral hemisphere. 2) DL stimulation produced the maximal potentials rather medially, while VL stimulation evoked the maximal potentials rather antero-laterally on the ipsilateral hemisphere. The same study was performed on CM stimulation in four patients with intractable pain. Stimulation of the parvocellular portion did evoke potentials but not so high as to be able to make spacio-temporal maps, while that of the magnocellular portion produced the clear evoked potentials.