The use of chronically implanted electrodes for the treatment of pain accompanying terminal carcinoma1has made it possible to investigate some aspects of thalamic function in the unanesthetized human. Following the first use of the stereotactic technique in the human by Kirschner in Germany in 1933, the work of Spiegel and Wycis in this country and of such workers as Leksell in Sweden, Riechert and Hassler in Germany, Talairach in France, and Narabayashi in Japan has well demonstrated the value of this method, not only for the clinical goal of producing discrete lesions in intracerebral structures, but also for investigating those brain functions which can be revealed by direct electrical stimulation. The work of Heath and collaborators2in demonstrating the feasibility of utilizing electrodes left in situ for weeks or months makes it possible to apply in man the principles initiated by Hess during many years of