Involvement of human thalamus in the preparation of self-paced movement.

Cortical areas participating in the preparation of voluntary movements have been studied extensively. There is emerging evidence that subcortical structures, particularly the basal ganglia, also contribute to movement preparation. The thalamus is connected to both the basal ganglia and the cerebellar pathways, but its role in movement preparation has not been studied extensively in humans. We studied seven patients who underwent deep brain stimulation (DBS) electrode implantation in the thalamus for treatment of tremor (six patients) and myoclonus-dystonia (one patient). We recorded from the DBS contacts and scalp simultaneously, while patients performed self-paced wrist extension movements. Post-surgical MRI was used for precise localization of the DBS contacts in six patients. Back-averaging of the scalp recordings showed a slow negative movement-related potential (MRP) in all patients (onset 1846 +/- 189 ms prior to electromyography onset), whereas DBS electrode recordings showed pre-movement MRP in five out of seven patients. The thalamic MRP preceded both contralateral and ipsilateral wrist movements. There was no significant difference between the onset time of thalamic MRP (-2116 +/- 607 ms) and cortical MRP. Neither the scalp nor the thalamus showed pre-movement potentials with passive wrist extensions in two patients. In four patients with postoperative MRI who had thalamic MRP, the maximum amplitude or phase reversal occurred at contacts located in the ventral lateral nucleus. Frequency analysis was performed in the five patients with thalamic MRP. The medial frontocentral scalp contacts and the thalamic contacts with maximum MRP amplitude showed two discrete frequency bands in the alpha (mean peak 9 Hz) and beta (mean peak 17 Hz) range. Both frequency bands showed pre-movement event-related desynchronization (ERD). In the grand average, alpha and beta ERD in the scalp and beta ERD in the thalamus began 2.5-2.8 s prior to the onset of movement. However, the thalamic alpha ERD began considerably later, at 1.2 s before EMG onset. The beta band showed cortico-thalamic coherence from the beginning of the baseline period until approximately 0.5 s before the onset of movement. There was no cortico-thalamic coherence in the alpha band. Our findings suggest that the cerebellar thalamus is involved early in the process of movement preparation. Different cortico-subcortical circuits may mediate alpha and beta oscillations. During movement preparation, the motor thalamus and the supplementary motor area predominantly interact in the beta band.

Localization of clinically effective stimulating electrodes in the human subthalamic nucleus on magnetic resonance imaging.

OBJECT: The authors sought to determine the location of deep brain stimulation (DBS) electrodes that were most effective in treating Parkinson disease (PD). METHODS: Fifty-four DBS electrodes were localized in and adjacent to the subthalamic nucleus (STN) postoperatively by using magnetic resonance (MR) imaging in a series of 29 patients in whom electrodes were implanted for the treatment of medically refractory PD, and for whom quantitative clinical assessments were available both pre- and postoperatively. A novel MR imaging sequence was developed that optimized visualization of the STN. The coordinates of the tips of these electrodes were calculated three dimensionally and the results were normalized and corrected for individual differences by using intraoperative neurophysiological data (mean 5.13 mm caudal to the midcommissural point [MCP], 8.46 mm inferior to the anterior commissure-posterior commissure [AC-PC], and 10.2 mm lateral to the midline). Despite reported concerns about distortion on the MR image, reconstructions provided consistent data for the localization of electrodes. The neurosurgical procedures used, which were guided by combined neuroimaging and neurophysiological methods, resulted in the consistent placement of DBS electrodes in the subthalamus and mesencephalon such that the electrode contacts passed through the STN and dorsally adjacent fields of Forel (FF) and zona incerta (ZI). The mean location of the clinically effective contacts was in the anterodorsal STN (mean 1.62 mm posterior to the MCP, 2.47 mm inferior to the AC-PC, and 11.72 mm lateral to the midline). Clinically effective stimulation was most commonly directed at the anterodorsal STN, with the current spreading into the dorsally adjacent FF and ZI. CONCLUSIONS: The anatomical localization of clinically effective electrode contacts provided in this study yields useful information for the postoperative programming of DBS electrodes.