Synchronization tomography: Synchronization analysis of MEG current density solutions in patients with Parkinson's disease

Abstract

Introdwtion The genesis of the parkinsonian resting tremor is not yet sufficiently understood. Using magnetoencephalography (MEG) and the magnetic field tomography (MIT) [l] Volkmann et al. [2] were able to localize cerebral activity that is time-locked to the EMG burst onset. Their results suggest that thalamic activity drives the supplementary motor area (SMA) and the premotor cortex (PMC), where both SMA and PMC drive the primary motor cortex (Ml). To analyze the dynamic interaction of cortical activty during epochs of tremor we applied our novel single-run synchronization analysis [3] directly to MEG signals measured in tremordominant PD patients [3]. In patients with alternating tremor we found pathological activity over motor areas in the 10 Hz range. This activity is 1:2 synchronized with the peripheral tremor activity (5 Hz range), whereas the different motor areas engaged in tremor generation are 1: 1 synchronized. The spatial resolution of this study was obvioulsy limited since no inverse modeling was involved. We here combine the two approaches to detect and localize both cortico-cortical and cortico-muscular synchronization processes with our novel synchronization tomography. Methods We simultaneously recorded MEG and EMG activity from 5 patients suffering from an early stage PD during periods of spontaneous tremor activity. MEG signals were recorded with the BTi Magnes 2500 whole-head system. Voxel by voxel we applied our single-run synchronization analysis [3] to the reconstructed cerebral current source density solutions obtained with the magnetic field tomography (MFI) [2]. Results We find a strong cortico-muscular synchronization between premotor areas (PMC, SMA) and sensorimotor areas (mainly Ml) on the one hand and the peripheral muscular activity on the other hand. In Patients with an alternating tremor the cortical activity is in the 10 Hz range, whereas in patients with a coactivation tremor it is in the 5 Hz range. Correspondingly, in patients with an alternating tremor we find a cortico-muscular 1:2 synchronization, and in patients with a coactivation tremor a cortico-muscular 1:l synchronization. The activity in the different motor areas engaged in tremor generation is 1:l synchronized. The strength of the cortico-muscular and cortico-cortical synchronization reflect the time course of the amplitude of the peripheral tremor.