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Cardiac Artifacts in Magnetoencephalogram

Jousmäki, Veikko; Hari, Riitta

Journal of Clinical Neurophysiology: March 1996 - Volume 13 - Issue 2 - p 172-176
Original Contribution

We studied cardiac contamination of magnetoencephalographic signals in eight healthy volunteers. The signals were recorded in a magnetically shielded room while the subject was sitting under a whole-scalp neuromagnetometer and were averaged time-locked to the R wave of the electrocardiogram. The maximum amplitude of the cardiac artifact varied between the subjects and was on average 130 fT/cm. The number of significantly contaminated channels was higher over the left than the right hemisphere. The electric and magnetic signals varied over time in the same way, implying that the artifacts are generated by cardiac currents, without any significant contribution from blood-flow-related pulsations or body movements. These artifacts may have a considerable effect on unaveraged data, i.e., recordings of spontaneous brain activity, and thus should be taken into account in the analysis.

Low Temperature Laboratory, Helsinki University of Technology, Espoo, Finland

Address correspondence and reprint requests to Mr. V. Jousmäki at Low Temperature Laboratory, Helsinki University of Technology, Otakaari 3A, FIN-02150 Espoo, Finland.

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