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.
The responses of neurons in the ventrolateral nucleus (VL) of the thalamus were studied in humans during performance of voluntary motor tests; recordings were made with microelectrodes during stereotaxic operations in patients with Parkinson's disease. Two previously classified types of polyvalent neurons (A, B) were found to show different patterns of responses during the functional stages of carrying out a voluntary movement (preparation, initiation, performance). A and B neurons showed concordant changes in the dynamics of ongoing network activity in the form of linked (activation-inhibition) and synergic (activation) response patterns, correlating with the preparation-trigger and performance phases of movements. It is suggested that the simultaneous activity of both types of neuron, with their common functional nature, reflects integrative processes occurring in the ventrolateral nucleus and associated with programming and processing of general signal parameters but not with the performance of any particular movement. The anterior (Voa nucleus) and posterior (Vop) parts of the ventrolateral nucleus were found to have different roles in organizing voluntary movements, associated with differences in their cellular organization and mechanisms of transmitting motor signals. It is suggested that the concordant changes in the activities of the two types of neurons in these areas seen during the performance of voluntary movements gives the ventrolateral nucleus a key role in the motor control system in humans.
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