The effect of saccadic eye movements on the sensor-level magnetoencephalogram

- The MEG signal elicited by the rotating eye dipoles is band-limited to below 30 Hz.
- The MEG signal created by the extraocular muscles are primarily monophasic pulses but they can be biphasic.
- For real data independent components need not clearly isolate the saccadic artifact.

ObjectiveWe used a combination of simulation and recordings from human subjects to characterize how saccadic eye movements affect the magnetoencephalogram (MEG).MethodsWe 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.ResultsThe 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 30 Hz 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 60 Hz.ConclusionsGamma 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.SignificanceWe 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.