The impulse activity of 183 multiunits was recorded from the premotor
cortex, the caudate nucleus, the globus pallidus, and the thalamus in
15 Parkinson's disease patients bearing inert gold electrodes implante
d for diagnosis and therapy. The patients performed a task in which st
imulus triplets (each consisting of two informational and one trigger
stimulus) were presented. The patients initiated or inhibited actions
(naming or counting) depending on the particular informational stimuli
, thus allowing discrimination between different components of multiun
it responses associated with attention and preparatory set and with di
sengagement from these states. The data indicate the existence of two
overlapping circuits: one responsible for preparation for and assessme
nt of the behavioral meaning of the stimulus and the other responsible
for preparation for and performance of verbal action.