ANALYSIS OF SPONTANEOUS ACTIVITY PATTERNS OF HUMAN THALAMIC VENTROLATERAL NEURONS AND THEIR MODIFICATIONS DUE TO FUNCTIONAL BRAIN CHANGES

In the human thalamic ventralis lateralis nucleus the spontaneous acti vity of 235 single units during 38 stereotactic operations in locally anaesthetized parkinsonian patients was analysed. Two basic cell types (A and B) were shown to exist in this nucleus: (i) with unitary irreg ular (2-40/s) discharges characterized by a tendency to spike grouping in the range of 4-6 Hz and 10-30 Hz (A-type, 74%), (ii) with bursting discharges firing in short trains (5-30 ms) characterized by an unsta ble rhythmic 3-6 Hz pattern similar to a low-threshold Ca2+ intrinsic burst structure of discharges (B-type, 26%). The functional brain chan ges after a motor tests performance were accompanied by the appearance of two different transient modifications of activity of A-cells patte rn into rhythmic burst discharges: (i) in the range of 3-6 Hz. similar to the bursts found for B-cells and recorded mainly in the anterior v entrolateral region in rigid patients, (ii) in the range of 5 +/- 1 Hz , characterized by other interspike interval and recorded in the poste rior ventrolateral region in patients with tremor. Modifications durin g short-term anaesthesia resulted in 10-15 Hz burst discharges that we re associated with gradual disappearance of A-cells activity. In contr ast to what happens for A-cells, the activity of bursting B-units was characterized by an invariant intrinsic structure of discharges irresp ective of the Functional brain changes or the forms of parkinsonian pa thology. The nature of A- anti B-units as well as the mechanisms of tr ansient modifications of their spontaneous activity patterns due to th e functional brain changes are discussed. (C) 1998 IBRO. Published by Elsevier Science Ltd.