CENTRAL MOTOR LOOP OSCILLATIONS IN PARKINSONIAN RESTING TREMOR REVEALED BY MAGNETOENCEPHALOGRAPHY

A variety of clinical and experimental findings suggest that parkinson ian resting tremor results from the involuntary activation of a centra l mechanism normally used for the production of rapid voluntary altern ating movements. However, such central motor loop oscillations have ne ver been directly demonstrated in parkinsonian patients. Using magneto encephalography, we recorded synchronized and tremor-related neuromagn etic activity over wide areas of the frontal and parietal cortex. The spatial and temporal organization of this activity was studied in seve n patients suffering from early-stage idiopathic Parkinson's disease ( PD). Single equivalent current dipole (ECD) analysis and fully three-d imensional distributed source solutions (magnetic field tomography, MF T) were used in this analysis. ECD and MFT solutions were superimposed on high-resolution MRI. The findings indicate that 3 to 6 Hz tremor i n PD is accompanied by rhythmic subsequent electrical activation at th e diencephalic level and in lateral premotor, somatomotor, and somatos ensory cortex. Tremor-evoked magnetic activity can be attributed to so urce generators that were previously described for voluntary movements . The interference of such slow central motor loop oscillations with v oluntary motor activity may therefore constitute a pathophysiologic li nk between tremor and bradykinesia in PD.