Functional Mapping with Simultaneous MEG and EEG

Summary

We use magnetoencephalography (MEG) and electroencephalography (EEG) to map brain areas involved in the processing of simple sensory stimuli.

Abstract

We use magnetoencephalography (MEG) and electroencephalography (EEG) to locate and determine the temporal evolution in brain areas involved in the processing of simple sensory stimuli. We will use somatosensory stimuli to locate the hand somatosensory areas, auditory stimuli to locate the auditory cortices, visual stimuli in four quadrants of the visual field to locate the early visual areas. These type of experiments are used for functional mapping in epileptic and brain tumor patients to locate eloquent cortices. In basic neuroscience similar experimental protocols are used to study the orchestration of cortical activity. The acquisition protocol includes quality assurance procedures, subject preparation for the combined MEG/EEG study, and acquisition of evoked-response data with somatosensory, auditory, and visual stimuli. We also demonstrate analysis of the data using the equivalent current dipole model and cortically-constrained minimum-norm estimates. Anatomical MRI data are employed in the analysis for visualization and for deriving boundaries of tissue boundaries for forward modeling and cortical location and orientation constraints for the minimum-norm estimates.

Protocol

1. Check system tuning and data quality

1. Check the tuning of the MEG system. Use the tuning and noise measurement software provided with the MEG system to check that all channels are properly tuned and that the average noise level is below 3 fT/cm or 3 fT on planar gradiometer and magnetometer MEG channels, respectively.
2. Collect a segment of empty room data. Acquire data with the shielded room void of subject for 5 minutes for quality assurance and noise estimation.

2. Set up the stimuli and data acquisition parameters.

1. Set up the somatosensory, auditory, and visual stimuli using a stimulus comput....

Discussion

Magnetoencephalography (MEG) and electroencephalography (EEG) are the only non-invasive methods to record brain activity with a fine temporal resolution. MEG is especially well suited for studying cortical activity. This article demonstrates combined MEG/EEG data acquisition and analysis to determined brain activity associated with the processing of simple sensory stimuli. These type of experiments are used both in basic neuroscience and clinical studies. If the brain activation is focal, the current dipole model applies.......