An analysis of the spontaneous rhythmic and non-rhythmic burst discharges in the human thalamus

Abstract

The patterns of spontaneous unitary activities recorded extracellularly in and around the ventralis intermedius nucleus of the human thalamus during the course of stereotaxic surgery on patients with Parkinsonism (PA), cerebral palsy (CP) and with other diseases are described. The discharge patterns were classified into two groups, viz., those which discharged continuously, mostly in random fashion, and those which fired repetitively in bursts. From a statistical pattern analysis, the latter were further classified into rhythmic and non-rhythmic burst discharges. Although the rhythmic burst discharges were found more in alert PA cases, they also existed in anaesthetized CP cases. In PA as well as CP cases, they were recorded mostly in the thalamic area, probably corresponding to the ventralis intermedius nucleus. Maximal effort could be made to alter the pattern of rhythmic burst discharges, but in general, they were not influenced by natural stimuli applied peripherally nor by mental effort on the part of the patient. By contrast, non-rhythmic burst discharges seemed to be abundant in anaesthetized CP cases. They were found in almost the same area as were the rhythmic bursts, sometimes, intermingling with each other. Some of these stopped firing when strong stimuli were applied to the contralateral or ipsilateral limbs. Several points relating to the mechanism of tremor are discussed.