Transcranial Direct Current Stimulation and Simultaneous Functional Magnetic Resonance Imaging

The overall goal of the following experiment is to illustrate the implementation of transcranial direct current stimulation or TDCS during simultaneous functional magnetic resonance imaging. To assess how the stimulation affects human brain functions, the first step involves assembling the necessary equipment, which includes MRI, compatible cables, electrodes, and filter boxes. As a second step, the TDCS equipment needs to be set up inside and outside of the scanner.

Next, the participant is screened and prepared for intra scanner TDCS. After the participant has been moved into the scanner bore, the stimulation is turned on and the FMRI experiment commences. Ultimately, the results of participants scanned during A-T-D-C-S are compared in a, within subjects design to results obtained during a separate sham TDCS session to reveal the impact of the stimulation on functional brain activity.

The main advantage of intra disease compared to purely behavioral TS protocols that it allows studying the neuronal mechanism underlying the simulation effects. In addition, compared to other neuro imaging techniques like E-E-G-F-M-R-I offers superior spatial resolution and also allows verification of the electrode position on thecal. The combined use of FMRI and TDCS can help unravel the neural mechanisms associated with TDCS action in the healthy brain, and also in a number of different pathological conditions like stroke or dementia.

Understanding how TDCS works in the brain may, may eventually improve clinical applications of this technique Because a number of critical steps need to be executed in the correct order in a time sensitive manner. Good planning and familiarization with these steps is necessary for successful implementation. If properly executed, the technique poses only minimal risk to participants.

However, researchers have to make sure to follow established MRI and TDCF safety guidelines. The experimental design consists of two FMRI segments performed during T-D-C-S-A five minute resting state sequence and an 11 minute overt semantic word generation task. The 20 minute at TDCS begins approximately one to two minutes prior to the scans, covers the entire duration of the two functional scans, and also short breaks and instructions in between scans.

Additional structural scans are acquired following the resting and task F MRIs. The sham stimulation session consists of 30 seconds of TDCS prior to the resting state FMRI with no TDCS during the remainder of the protocol for the language task, use stimulus presentation software to project a visual image of various semantic categories to a screen inside of the scanner. The projection is accomplished via a projector and a system of mirrors connected to the computer.

An MRI compatible microphone is used for transmission of overt verbal responses. To set up the TDCS device program, the device to deliver a constant direct current of one milliamp for 20 minutes ensure that the stimulator is sufficiently charged. Otherwise, it may shut down during the experiment, assemble all of the equipment, cables, and electrodes necessary for the TDCS as described in the text protocol.

In the MRI control room, place the outer filter box close to the RF filter tube that is used to pass cables into the scanner room. Note that the outer filter box is clearly labeled. The inner and outer filter box must not be mixed up.

Next, connect the stimulator to the outer box using the stimulator cable. Measure the length of box cable required to connect the inner and outer filter boxes, allowing enough cable to run along the walls of the scanner room. Insert the box cable into the RF filter tube and connect it to the outer filter box in the scanner room.

Place the inner filter box inside the rear end of the scanner bore and use adhesive tape to keep it in place. Attach the box cable to the walls with an adhesive tape and connect it to the inside scanner Filter box, avoiding any loops in any cables as these may induce RF heating.Thoroughly. Screen participants for MRI and TDCS contraindications, such as pacemakers, middle in the body, and claustrophobia.

After explaining the procedure, obtain informed as with conventional TDCS setups to prepare for electrode placement. Inspect the participant's skin for any pre-existing lesions and move any hair away. Then clean the skin with alcohol to improve skin condition.

After soaking the sponge pockets with saline solution, insert the MRI compatible electrodes into the pockets using a pen that leaves non faro magnetic traces. First, mark the intersection of T three F three and F seven C3 on the subject's head, and then mark the midpoint between F seven and F three. Now mark the center of a line connecting those two points and place the anode at this point.

Then place the cathode over the right supraorbital position and attach both electrodes with a rubber band. After a final safety check outside of the scanner, guide the participant inside the scanner room and then close to the scanner to connect the electrode cable to the inner filter box. Next, turn on the stimulator and test the impedance, for example, by pressing the upper right and lower left button of the stimulator simultaneously.

Impedances are typically higher during this procedure compared to standard T DS S protocols because of higher resistance of cable length and filter boxes, so it's critical to test impedances prior to commencement of scanning. If the impedance limits are reached, then the stimulator stops automatically if this occurs. Possible remedies include ensuring that the electrodes have contact with the scalp, cleaning the skin, again, applying more saline solution to the sponges.

Position the participant on the scanner gantry. Make sure that the electrodes are still in the correct position. Then feed the electrode cable through the lower left part of the head coil and secure the cable to ensure that it will not catch on the gantry.

As the gantry is moved. Close the head coil after that and hand the emergency button to the participant. Then slide the participant into the scanner.

Bore next, reach for the electrode cable from the rear end of the scanner and connect it to the inner filter box and leave the room. Use the scanner intercom to inform the participant about the start of the scanning session. Start the structural localizer scan using the scanning console after the end of the acquisition period.

Inspect the localizer scan for high frequency artifacts by double clicking on the localizer scan and adjusting the contrast by holding the right mouse button while moving the mouse to the left and right. Use the scanner intercom to communicate to the subject that the stimulation will commence and that he or she might feel a tingling sensation on the scalp for a short time. Then repeat the instructions for the first functional scan.

For the resting state scan, instruct the participant to keep his or her eyes closed for the duration of the five minute scan. To move as little as possible and to think of nothing in particular. Also, make sure that the projector is turned off manually.

Start the TDCS approximately one to two minutes prior to the start of the resting state functional scan. Use the scanner console to load the resting state sequence. Double click on the resting state sequence to open the field of view and adjust the position to cover the entire brain and to align approximately with the anterior posterior commissure.

Now, start the first scan. Monitor the impedance throughout the experiment using a second researcher when performing double blind studies while the resting state sequence is running. Load the second functional imaging sequence, which is the language task, and adjust the field of view as before using the scanner console to reduce the time required in between scans.

After the end of the resting state sequence, turn on the projector to allow for the visual display of the experimental stimuli during the language task. Double click on the presentation software icon and load the language paradigm. Use the scanner intercom to repeat the instructions for the task related FMRI paradigm and commence with the task at the end of the stimulation and FMRI experiment.

Continue with the planned structural scans. At the end of the experiment, disconnect the electrode cable from the inner filter box before moving the participant out of the scanner bore. Then detach the head coil and ask the participant to sit up and remove the electrodes carefully.

FMRI studies during a semantic word generation task showed reduced activity in the ventral portion of the inferior frontal gyrus in both younger and older adults who received A-T-D-C-S as compared to when the same subjects were scanned during sham stimulation. No significant differences were found in the left dorsal inferior frontal gyrus and FMRI. Resting state scan performed during A-T-D-C-S as compared to a resting state scan acquired in the same 18 participants during a separate sham TDCS session illustrates brain regions showing enhanced connectivity during A-T-D-C-S indicated in red and regions showing reduced connectivity indicated in blue.

In the future, this new technique may be used in clinical populations to enhance the effectiveness of existing interventions or to develop new scientifically grounded protocols. To further our understanding of the underpinning effects of TT CS, this technique could complemented by other techniques such as EEG TT S in order to exploit the superior temporal resolution of these techniques. After watching this video, you should have a good understanding of the technical requirements, the implementation, and the safety considerations of the combined use of TDCS and MRI.