Background spike activity of 235 cells of the integrative subcortical motor center, i.e., the ventrolateral nucleus of the thalamus, were analyzed in nonanesthetized human brains during stereotaxic surgery in patients with various forms of Parkinson's disease. Previous data on the existence of two major types of neurons with convergent properties in the ventrolateral nucleus were confirmed. These cell types are: 1) cells with irregular occasional activity, with a tendency for spikes to group into the frequency ranges 5 +/- 1 and 10-30 Hz (type A cells, 74%), and 2) cells with constant rhythmic (3-6 Hz) generation of short volleys of discharges, with an interval structure similar to that of low-threshold Ca(2+)-dependent volley activity (type B, 26%). This is the first report demonstrating that changes in the functional state of the brain (after repeated movement trials, in transient anesthesia) are accompanied by transiently occurring transformations of the initial irregular activity of A cells into a rhythmic, volley-like pattern whose interval structure was in some cases similar to the spike activity of B cells. Differences in the localizations of A and B neurons in the ventrolateral nucleus are described, along with differences in the correlation characteristics of their background spike activity with the pathological features of Parkinson's disease (tremor, rigidity). The nature of the two types of convergent neurons in the ventrolateral nucleus is discussed, and a basis is laid for the importance of the functional factor in understanding the transformation of their background spike activity, due to the properties of cell membranes and intercellular and interstructure interactions in conditions of the living nonanesthetized human brain.