Magnetic vestibular stimulation can be used for studying vestibular cognitive interactions in healthy people and also in vestibular patients. This method quantifies the influence of magnetic vestibular stimulation on perception and cognition by assessing eye movements subjective self motion reports and the orientation of the inner ear in the MRI scanner. Generally, tilting the head forward during MRI scans can help to reduce dizziness making the scanning less unpleasant.
The effects of magnetic vestibular stimulation can be useful for clinical research. To begin, connect the experimental and eye tracking computer with a crossover ethernet cable. To enable the synchronization of data collection.
Switch on the projector connected to the experimental computer. Connect the magnetometer device to the magnetometer computer by plugging it into the USB connector. Connect the eye tracking goggles to the eye tracking computer with a shielded fire wire cable.
Then open the eye tracking software to prepare the participant for entering the magnetic resonance imaging or MRI scanner. Confirm that the participant does not meet MRI exclusion criteria. Provide MRI safe clothing and remove metallic objects.
Remove contact lenses, eyeshadow, mascara and clean the eyes for better eye tracking. Put an elastic headband and EEG cap on the participant's head. Then fix the magnetometer behind one ear by pulling it under the elastic headband and the EEG cap with adhesive tape.
Let the participant insert the ear plugs. Put on the eye tracking goggles over the EEG cap. Then adjust the focus on the goggles before adjusting the eye tracking parameters on the goggles and in the software to ensure good tracking, let the participants sit one meter in front of the calibration stimuli and measure the eye stimulus distance with a measuring tape.
Adjust the eye tracking parameter as described earlier. Press record to start data acquisition. Let the participant look at every dot for one second with verbal instruction of left, down, mid, up and right then press stop.
To stop data acquisition. Put the goggles cover on and ensure that the participant cannot see any light. Adjust the eye tracking parameters.
Press start recording to measure the eye movements for 30 seconds. After the acquisition, press stop recording and take the goggles cover off. Adjust the head tilt position of the participant according to the first condition in supine by using appropriate cushions.
Place the mirror over the participant's head and adjust it so the screen is inside the participant's field of view. Then give the participant the response buttons for each hand. If necessary, fix the button with tape.
Next, let the participant practice putting on and taking off the cover of the goggles so that this can be done in the dark. Inside the bore. Adjust the MRI beds starting position with the help of the MRI scanners.
Laser cross, such that the participants'inner ear structure is in the center of the bore during the experiment. Before the run, instruct the participant about the run. Start the self motion perception paradigm by pressing run and entering the participant and trial information in the software on the computer.
Start the eye tracking measurements by pressing record in the eye tracking software. Instruct the participant to open their eyes widely. Then start the magnetometer measurements by pressing record in the magnetometer software.
After instructing the participant that the run is starting move the participant into the bore and measure the eye movements of participant while entering the magnetic field. After three minutes, percepts of self motion should have vanished in most participants. Therefore, tell the participants to take the goggles cover off if visual stimuli need to be presented.
If applicable, present a self motion questionnaire or a cognitive task on the screen by starting it by pressing run on the computer and letting the participant answer via response buttons. Instruct the participant to put the goggles cover on. Move the the participant out of the scanner.
Let the participant take off the covers of the goggles. Then repeat the procedure for a self motion questionnaire on the screen. Switch the head position to the other head position using the appropriate cushions and repeat the same procedure.
Remove the mirror and goggles without replacing the magnetometer. Replace the magnetometer probe with a pipette filled with water without displacing the cover of the magnetometer. Then install the head coil.
Place the participant's head inside the head coil without displacing the magnetometer and move the participant into the scanner. Acquire a three-dimensional cyst sequence for structural inner ear imaging. Move the participant out of the MRI scanner.
The eye tracking data showed the captured horizontal and vertical eye movements. Calibration recordings were used to transform units from pixels to degrees. The data were of good quality.
If a steady tracking with 100 hertz is reached and the extracted data show only minor tracking artifacts. Data from the three dimensional magnetometer. Moving into the bore showed a maximum field strength of almost seven Tesla.
After approximately 27 seconds the tracked data appeared to be smooth and showed no alterations in field strengths in each rotation axis. After reaching the inside of the bore from the three-dimensional CYS images the three-dimensional surface models of magnetometer orientation and the right and left inner ears were extracted. The surface model allows for extracting the orientation of the semi semi-circular canals for the magnetometer orientation and the Z axis of the magnetic field.
The results can give us an insight into the interaction between vestibular inflammation and cognitive processes in spatial cognition and the immersions of self motion perception on the conflicting sensory information Assessing the effects of magnetic vestibular stimulation in the MRI requires a careful planning and has to be adjusted to the research side. Ultra highfield MRI imaging of the inner ear adds very helpful information about the orientation of the vestibular system in the magnetic field.
