Functional Mapping with Simultaneous MEG and EEG

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.