Physiological observations made in man offer a unique opportunity to understand the motor thalamus. On the one hand, the patient can describe what he feels when a site is stimulated; on the other, one can observe any induced motor effect, both in 'normal' patients and in those with movement disorders. Finally, all this can be correlated with single unit recordings at the same site. Data has been correlated relative to the motor thalamus from over 10,000 macrostimulation sites and from 114 patients undergoing microstimulation and microrecording, in an attempt to understand something of the function of this part of the brain.