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Removal of the Cardiac Cycle Artefact and Subsequent Coupling Analysis between Cortex and Basal Ganglia
Zitatschlüssel Bock20150
Autor Bock, Antje
Jahr 2013
Notiz Simultaneous Magnetoencephalographic and Intracranial Local Field Potential Recordings in Patients with Movement Disorders undergoing deep Brain Stimulation
Schule Charité Unviersitätsmedizin Berlin
Zusammenfassung Simultaneous magnetoencephalography (MEG) and intracranial local field potential recordings in patients with severe movement disorders undergoing deep brain stimulation (DBS) treatment are a promising tool both for clinical application and basic research. Recordings can be accomplished during the time interval (two to five days) between electrode insertion and its connection to the subcutaneous pulse generator while electrodes are externalised. Thusly, interactions between the DBS targets and cortical areas can be uncovered to understand physiological and pathophysiological loops. DBS target points are the subthalamic nucleus or the caudal zona incerta for Parkinson’s disease patients and the internal globus pallidus for dystonic patients. Coupling measures such as coherence (coh) and the imaginary part of coherency (icohy) have been applied. However, at lower frequencies below 10 Hz strong cardiac cycle artefacts (CCAs) are observed in the MEG signals around the area of the burr holes in the left hemisphere, where both disposable stainless steel electrodes wires leave the skull. The CCA refers to the remanent magnetic field of those wires underneath the MEG sensors, which are moved by local pulsations of the blood vessels. The present thesis essentially aims at accurately identifying the extent of this artefact and providing and comparing three different methods of its removal from the MEG sensor space: (i) Applying principal component analysis and subsequent signal space projection (SSP) method to the CCA in time space (tCCA); (ii) applying independent component analysis; and (iii) applying SSP to the CCA in frequency space (fCCA). Subsequently, solely the ispilateral coh and icohy between the target points located within the basal ganglia and cortical areas of the right hemisphere, which shows less artefacts, were calculated once more. Based on the a priori assumption that the artefact mainly covers coh and icohy below 10 Hz, preferable removal characteristics would be a strong suppression below 10 Hz while preserving or yet uncover coupling above 10 Hz. In particular after applying the tCCA removal method, typical topographic dipolar and bipolar patterns in the α (8 to 12 Hz) and β (13 to 30 Hz) frequency ranges are well preserved, whereas artefactual patterns below 10 Hz are significantly suppressed. Results of disease-specific coupling differences are mostly in line with previous findings. Consequently, over and above the technical feasibility of this highly challenging set-up, especially the tCCA removal method is an appropriate tool and clears the way for more precise and more extensive coupling analyses using similar data sets.
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