Synchrony of rest tremor in multiple limbs in Parkinson's disease: evidence for multiple oscillators

Recent evidence points to involvement of central nervous system oscillators in Parkinson's disease (PD) rest tremor. It remains unknown whether one or multiple oscillators cause tremor in multiple limbs. Based on the predicti on that multiple oscillators would cause low coherence even with similar av erage frequency, we studied 22 PD patients using accelerometers on multiple limbs. Records were digitized and spectral analysis was performed. Peak fr equencies in the arms, legs, and chin were similar, indicating that biomech anical factors did not determine the frequency. Coherence between different axes of individual accelerometers and between different segments of the sa me limb was high. However, coherence between tremor in different limbs was low. There was no consistent pattern across patients of ipsi- vs. contralat eral predominance of coherence. These data suggest that tremor in PD is gen erated by multiple oscillatory circuits, which operate on similar frequenci es.