Subthalamic prelemniscal radiation stimulation for the treatment of Parkinson's disease: Electrophysiological characterization of the area

Background. Previous reports have provided evidence of a reticulo-thalamic system, extending from the mesencephalic reticular formation (MRF) to the v entrolateral thalamus (VL), involved in the production of tremor. In humans , a funnel of fibers in the posterior subthalamus named the prelemniscal ra diations (Raprl) has been described as an exquisite target to treat tremor in cases of Parkinson's disease. Methods. In the present study, a group of 14 patients suffering from Parkin son's disease, with prominent unilateral tremor and rigidity, were implante d with tetrapolar depth brain stimulation (DBS) electrodes in Raprl to perf orm chronic electrical stimulation (ES) for the treatment of patient sympto ms. Electrodes were left externalized to corroborate their placement throug hout MRT studies and also to perform the following electrophysiological bat tery: (a) recording of somatosensory-evoked responses (SEP) through differe nt electrode contacts and scalp by means of a paradigm to study the attenti on process; Cb) evoking scalp EEG responses by stimulation with low (3 cps, 6 cps) and high (60-120 cps) frequencies with stimuli delivered through di fferent electrode contacts, and (c) studying recovery cycle (RC) potentials in the Raprl while the upper MRF was being stimulated and, conversely, the RC in MRF while Raprl was being stimulated, before and after subacute Rapr l stimulation. Thereafter, the electrodes were internalized and connected t o a pulse generator (IPG) to carry on chronic ES, while the effects of stim ulation were determined through a quantitative evaluation that measured pha sic and tonic muscular activity with EMG recordings during different motor tasks. Results. Results indicate the following: (a) that late, but not early, SEP components were recorded in Raprl and modulated in different attentive cond itions; (b) that bilateral recruiting responses and spike and wave complexe s were elicited by Raprl through low-frequency stimulation, while bilateral positive DC shifts induced by high-frequency stimulation were recorded, si milar to those obtained in animals from MRF, and (c) that Raprl-ES induced RC inhibition at Raprl, but Raprl ES did not change MRF-RC. Long-term Raprl -ES induced a significant decrease in tremor and rigidity. Conclusions. It was concluded that Raprl represents a subthalamic circuit e lectrophysiologically related to MRF in the genesis of tremor and rigidity and in the process of selective attention. Raprl-ES induced a significant i mprovement in tremor and rigidity by causing inhibition of the stimulated a rea. (C) 2000 IMSS. Published by Elsevier Science Inc.