Name: Functional Mapping with Simultaneous MEG and EEG (Video) | JoVE Journal
Uploaded: 2010-06-14T19:00:00.000+00:00
Duration: 6 min 4 s
Description: Learn simultaneous MEG and EEG techniques to map sensory processing brain regions in healthy individuals and epilepsy patients. This protocol reveals neural mechanisms underlying perception and informs clinical surgical decisions.

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5 minutes

1. Check system tuning and data quality
<ol>
<li>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.</li>
<li>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.</li>
</ol>
2. Set up the stimuli and data acquisition parameters.
<ol>
<li>Set up the somatosensory, auditory, and visual stimuli using a stimulus computer, projector installed outside the shield room, and a somatosensory electric stimulator (Grass Model S88).</li>
</ol>
3. Subject preparation
<ol>
<li>Before an MEG/EEG study, each subject must fill out several forms regarding safety and consent.</li>
<li>Check that subject is free of magnetic materials. Bring the subject into the shielded room and start MEG data acquisition to check that the data does not contain signs of magnetic artifacts. If necessary, use a degausser to reduce artifacts from magnetic objects in the body such as dental work.</li>
<li>Put on EEG cap, inject conducting gel, and check the impedances. The impedances should be below 10 kOhms.</li>
<li>Put on EOG electrodes and the reference electrode.</li>
<li>Put on head-position indicator (HPI) coils. Position the four HPI coils so that they will be under the area covered by the MEG sensor array and far away from each other.</li>
<li>Digitize fiducial landmarks, HPI coils, EEG electrodes, and head shape.</li>
<li>Move the subject into the scanner.</li>
</ol>
4. Data acquisition for each sensory modality
<ol>
<li>Set up stimulation protocols on the stimulus computer. For the somatosensory median-nerve stimulation, attach the electrodes on the left and right wrists and gradually increase the stimulus intensity so that the stimulus level exceeds the motor threshold. For the auditory stimulation, insert the earphones and check that the stimulus level is appropriate. For the visual stimulation, position the back-projection screen in front of the subject and check that the stimulus is correctly presented.</li>
<li>Start data acquisition and check data quality. On the raw data display, check that all channels are functioning properly and do not contain any artifacts.</li>
<li>Measure the head position. Invoke the head position measurement from the acquisition console and check that the results meet the specifications imposed by the software.</li>
<li>Start saving of raw data and on-line averaging.</li>
<li>Start stimulus delivery</li>
<li>Once all stimuli have been presented, save raw data and on-line averages.</li>
</ol>
5. Data analysis
In the data analysis, we will use anatomical MRI data for visualization of the results, for determining the shapes of tissue compartments for forward modeling, and for constraining the lMEG/EEG data to the cortical surface. We use both the current dipole model and a distributed cortically constrained minimum-norm solution in the analysis. The workflow of the distributed source analysis is shown in Figure 1. 
<img src="/files/ftp_upload/1668/1668fig1.jpg" alt="MEG/EEG source analysis workflow diagram; MRI/MEG data, cortical geometry, inverse operator." data-altupdatedat="1788235205000" data-alt="figure 1"> Figure 1. Overall workflow for analyzing MEG/EEG using cortically-constrained minimum-norm estimates.

<ol><li>Hämäläinen, M., Hari, R., Ilmoniemi, R., Knuutila, J., Lounasmaa, O. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Magnetoencephalography+-+theory%2C+instrumentation%2C+and+applications+to+noninvasive+studies+of+the+working+human+brain%5BTitle%5D)+AND+%22Reviews+of+Modern+Physics%22%5BJournal%5D)">Magnetoencephalography - theory, instrumentation, and applications to noninvasive studies of the working human brain.</a> Reviews of Modern Physics. 65, 413-497 (1993).</li>
<li>Hämäläinen, M., Hari, R. Brain Mapping, The Methods. Toga, A. W., Mazziotta, J. C. , Academic Press. 227-253 (2002).</li>
<li>Sharon, D., Hämäläinen, M., Tootell, R. B., Halgren, E., Belliveau, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+advantage+of+combining+MEG+and+EEG%3A+Comparison+to+fMRI+in+focally+stimulated+visual+cortex%5BTitle%5D)+AND+%22Neuroimage%22%5BJournal%5D)">The advantage of combining MEG and EEG: Comparison to fMRI in focally stimulated visual cortex.</a> Neuroimage. 36, 1225-1235 (2007).</li>
<li>Mäkelä, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Three-dimensional+integration+of+brain+anatomy+and+function+to+facilitate+intraoperative+navigation+around+the+sensorimotor+strip%5BTitle%5D)+AND+%22Human+Brain+Mapping%22%5BJournal%5D)">Three-dimensional integration of brain anatomy and function to facilitate intraoperative navigation around the sensorimotor strip.</a> Human Brain Mapping. 12, 180-192 (2001).</li>
</ol>

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...

functional mapping with simultaneous meg and eeg

Functional Mapping with Simultaneous MEG and EEG

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.

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

We use magnetoencephalography (MEG) and electroencephalography (EEG) to locate and determine the temporal evolution in brain areas involved in the ...

Hi, I am Markham from the Martino Center at Massachusetts General Hospital. Hi, I'm Han Liu, also from the Martino Center. Today we'll show you a protocol for collecting and analyzing MEC and EC data using auditory somatosensory.And this was stimulated to locate the primary sensory COIs. We use this procedure in our lab to study both the healthy volunteers and the AP epilepsy patients who are candidates for surgery. So let's begin.Begin by checking the tuning of the MEG system. Ensure that all channels are properly tuned and that the average noise level is below three femto Teslas per centimeter on Plano gradiometer channels, and below three femto Teslas on magnetometer channels. Next, collect a segment of empty room data for five minutes to obtain an estimate of background noise.Now set up the somatosensory auditory and visual stimuli that will be presented to the subject during the experiment. This is achieved with a stimulus computer, a projector installed outside the shield room and a somatosensory electric stimulator. To prepare the subject for the experiment first, ensure that they are free of magnetic materials, and then bring them into a shielded room and acquire some MEG data to check that there are no signs of magnetic artifacts.Now that the subject is free of any artifacts, place the EEG cap on the subject's head and inject conducting gel into each electrode. Once the cap is in place and ready, attach the EOG electrodes and the reference electrode and check that the impedances of EEG and all the other electrodes are below 10 kilo rooms. Next place the head position indicator or HPI coils position them so that they will be under the area covered by the MEG sensor array and far away from each other.Now digitize the fiduciary landmarks, HPI coils, EEG electrodes and head shape. This step is done outside the magnetically shielded room, containing the MEG system using a 3D digitizer device. Finally, place the subject into the scanner.With preparations finished, let's begin acquiring data. To begin set up the stimulation protocols on the stimulus computer for somatosensory median nerve stimulation. Attach the stimulation electrodes to the left and right wrist of the subject, and gradually increase the stimulus intensity under the level exceeds the motor threshold for auditory stimulation.Place earphones onto the subject's ears and check that the volume is appropriate for visual stimulation. Position the back projection screen in front of the subject and check that the stimulus is correctly presented. Now begin acquiring data on the raw data display.Check that all the channels are functioning properly and do not contain any artifacts. Present the stimuli to the subject and then save the raw data on online averages. In the data analysis, we use anatomical MRI data to determine the shapes of tissue compartments for forward modeling and to constrain the M-E-E-G-E-E-G data to the cortical surface.We use both the current dipole model and a distributed cortically constrained minimum norm solution. Locating the brain areas, responding to the stimulation. We have just shown you how to collect and analyze EG and EG data in response to visual, auditory, and some other sensory ti.We have demonstrated how these data can be analyzed to locate the primary sensory corsis. So that's it. Thank you for watching and good luck in your experiments.

functional-mapping-with-simultaneous-meg-and-eeg

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Learn simultaneous MEG and EEG techniques to map sensory processing brain regions in healthy individuals and epilepsy patients. This protocol reveals neural mechanisms underlying perception and informs clinical surgical decisions.

Functional Mapping with Simultaneous MEG and EEG

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