Timothy J Gawne1, Jeffrey F Killen2, John M Tracy3, Adrienne C Lahti4. 1. Dept. Optometry and Vision Science, University of Alabama at Birmingham (UAB), Birmingham, AL, USA. Electronic address: tgawne@gmail.com. 2. HSF Neurology, University of Alabama at Birmingham (UAB), Birmingham, AL, USA. 3. Dept. Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham (UAB), Birmingham, AL, USA; Dept. Psychiatry, Vanderbilt University, Nashville, TN, USA. 4. Dept. Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham (UAB), Birmingham, AL, USA.
Abstract
OBJECTIVE: We used a combination of simulation and recordings from human subjects to characterize how saccadic eye movements affect the magnetoencephalogram (MEG). METHODS: We used simulated saccadic eye movements to generate simulated MEG signals. We also recorded the MEG signals from three healthy adults to 5° magnitude saccades that were vertical up and down, and horizontal left and right. RESULTS: The signal elicited by the rotating eye dipoles is highly dependent on saccade direction, can cover a large area, can sometimes have a non-intuitive trajectory, but does not significantly extend above approximately 30Hz in the frequency domain. In contrast, the saccadic spikes (which are primarily monophasic pulses, but can be biphasic) are highly localized to the lateral frontal regions for all saccade directions, and in the frequency domain extend up past 60Hz. CONCLUSIONS: Gamma band saccadic artifact is spatially localized to small regions regardless of saccade direction, but beta band and lower frequency saccadic artifact have broader spatial extents that vary strongly as a function of saccade direction. SIGNIFICANCE: We have here characterized the MEG saccadic artifact in both the spatial and the frequency domains for saccades of different directions. This could be important in ruling in or ruling out artifact in MEG recordings. Copyright Â
OBJECTIVE: We used a combination of simulation and recordings from human subjects to characterize how saccadic eye movements affect the magnetoencephalogram (MEG). METHODS: We used simulated saccadic eye movements to generate simulated MEG signals. We also recorded the MEG signals from three healthy adults to 5° magnitude saccades that were vertical up and down, and horizontal left and right. RESULTS: The signal elicited by the rotating eye dipoles is highly dependent on saccade direction, can cover a large area, can sometimes have a non-intuitive trajectory, but does not significantly extend above approximately 30Hz in the frequency domain. In contrast, the saccadic spikes (which are primarily monophasic pulses, but can be biphasic) are highly localized to the lateral frontal regions for all saccade directions, and in the frequency domain extend up past 60Hz. CONCLUSIONS: Gamma band saccadic artifact is spatially localized to small regions regardless of saccade direction, but beta band and lower frequency saccadic artifact have broader spatial extents that vary strongly as a function of saccade direction. SIGNIFICANCE: We have here characterized the MEG saccadic artifact in both the spatial and the frequency domains for saccades of different directions. This could be important in ruling in or ruling out artifact in MEG recordings. Copyright Â