19Gamma synchronization increases during movement and scales with kinematic parameters.
20Here, disease-specific characteristics of this synchronization and the dopamine-dependence of with symptom severity. In the dopamine-depleted state, gamma power and burst rate 28 significantly decreased, particularly when peak velocity was slower than ON medication.
29Burst amplitude and duration were unaffected by the medication state. We propose that
Primary dystonia has been associated with an underlying dysfunction of a wide network of brain regions including the motor cortex, basal ganglia, cerebellum, brainstem and spinal cord. Dystonia can be effectively treated by pallidal deep brain stimulation although the mechanism of this effect is not well understood. Here, we sought to characterize cortico-basal ganglia functional connectivity using a frequency-specific measure of connectivity-coherence. We recorded direct local field potentials from the human pallidum simultaneously with whole head magnetoencephalography to characterize functional connectivity in the cortico-pallidal oscillatory network in nine patients with idiopathic dystonia. Three-dimensional cortico-pallidal coherence images were compared to surrogate images of phase shuffled data across patients to reveal clusters of significant coherence (family-wise error P < 0.01, voxel extent 1000). Three frequency-specific, spatially-distinct cortico-pallidal networks have been identified: a pallido-temporal source of theta band (4-8 Hz) coherence, a pallido-cerebellar source of alpha band (7-13 Hz) coherence and a cortico-pallidal source of beta band (13-30 Hz) coherence over sensorimotor areas. Granger-based directionality analysis revealed directional coupling with the pallidal local field potentials leading in the theta and alpha band and the magnetoencephalographic cortical source leading in the beta band. The degree of pallido-cerebellar coupling showed an inverse correlation with dystonic symptom severity. Our data extend previous findings in patients with Parkinson's disease describing motor cortex-basal ganglia oscillatory connectivity in the beta band to patients with dystonia. Source coherence analysis revealed two additional frequency-specific networks involving the temporal cortex and the cerebellum. Pallido-cerebellar oscillatory connectivity and its association with dystonic symptoms provides further confirmation of cerebellar involvement in dystonia that has been recently reported using functional magnetic resonance imaging and fibre tracking.
The understanding of the interaction between muscle control and cortical areas and between subcortical and cortical areas is important for the effective treatment of patients with movement disorders. The combination of coherence (COH) and the imaginary part of coherency (iCOH) is applied here to electrophysiological data from patients with a movement disorder and to data from healthy subjects performing finger movements. The COH and iCOH between magnetoencephalographic (MEG) and electromyographic (EMG) signals of the healthy subjects yields the expected result for cortico-muscular coupling. Based on this the COH and iCOH between sub-thalamic nucleus local field potentials (STN-LFP) and MEG signals are assessed for deep brain stimulation patients with externalized LFP electrodes. The results suggest interactions in the 10 to 20 Hz range. Artificially mimicking volume conduction by re-referencing the STN electrodes to a surface EEG electrode leads to large changes in the COH and iCOH. This suggests that volume conduction is not important for the analysis of interactions between MEG and bipolar STN electrodes.
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