Central motor loop oscillations in parkinsonian resting tremor revealed magnetoencephalography

Abstract

A variety of clinical and experimental findings suggest that parkinsonian resting tremor results from the involuntary activation of a central mechanism normally used for the production of rapid voluntary alternating movements. However, such central motor loop oscillations have never been directly demonstrated in parkinsonian patients. Using magnetoencephalography, we recorded synchronized and tremor-related neuromagnetic activity over wide areas of the frontal and parietal cortex. The spatial and temporal organization of this activity was studied in seven patients suffering from early-stage idiopathic Parkinson's disease (PD). Single equivalent current dipole (ECD) analysis and fully three-dimensional distributed source solutions (magnetic field tomography, MFT) were used in this analysis. ECD and MFT solutions were superimposed on high-resolution MRI. The findings indicate that 3 to 6 Hz tremor in PD is accompanied by rhythmic subsequent electrical activation at the diencephalic level and in lateral premotor, somatomotor, and somatosensory cortex. Tremor-evoked magnetic activity can be attributed to source generators that were previously described for voluntary movements. The interference of such slow central motor loop oscillations with voluntary motor activity may therefore constitute a pathophysiologic link between tremor and bradykinesia in PD.

High Thalamocortical Theta Coherence in Patients with Parkinson's Disease

“…The pathophysiological effects of PD on the thalamus thus lead to a slowing of scalp EEG in PD patients (Soikkeli et al, 1991;Stanzione et al, 1996;Tanaka et al, 2000). Our results support the notion that the PD symptomatology originates from a disturbance in the thalamocortical interplay (Llinas, 1984;Volkmann et al, 1992Volkmann et al, , 1996Llinas and Pare, 1994;Jeanmonod et al, 1996;Llinas et al, 1999).…”

“…(5) In the final step, positive symptoms are produced (e.g., tremor) (Volkmann et al, 1992(Volkmann et al, , 1996. This step is thought to be related to the reciprocal corticocortical inhibition mediated by GABAergic interneurons, which is a general feature of cortical organization (Fig.…”

Enhanced frontal low and high frequency power and synchronization in the resting EEG of parkinsonian patients

“…The main output of the basal ganglia is indeed via the pallidothalamic tract into the thalamus. Due to a reduction of dopamine in the striatum, increased neuronal activity of the internal part of the globus pallidus (GPi) (Albin et al, 1989;Beric et al, 1996;DeLong, 1990;Hutchison et al, 1994;Lozano et al, 1998;Magnin et al, 2000;Sterio et al, 1994), causes a tonic overinhibition of the pallidal-recipient thalamic relay cells leading to a thalamocortical dysrhythmic interplay, named thalamocortical dysrhythmia (TCD), characterized by an overproduction of thalamic low threshold calcium spike bursts and an increase in low and high frequency EEG power (Jeanmonod et al, 1996Llinas, 1984;Llinas and Pare, 1994;Llinás et al, 2001;Llinás et al, 1999;Magnin et al, 2000;Volkmann et al, 1992Volkmann et al, , 1996.…”

Coherence and Source Localizationof Parkinsonian Resting Tremor

“…Network locations have been examined by EEG and MEG in patients with PD, however, the tremor origin has not been accurately located. It has been shown by MEG that a tremor correlates with cortical activities 14 . Hellwig et al 9 also showed tremor-correlated cortical activities in EEG recordings indicating significant coherency to the unilateral tremor in the contralateral motor cortex area.…”