Simultaneous Application of Transcranial Direct Current Stimulation during Virtual Reality Exposure

The combination of non-invasive brain stimulation with virtual reality presents a novel approach to augment emotional learning and habituation for people seeking treatment for post-traumatic stress and anxiety. This is a highly immersive yet portable approach rooted in neuroscience. The technique could be therapeutically effective and can be tailored to the individual patient.

This non-invasive method can help patients with post-traumatic stress learn that previously anxiety-provoking situations can be safe. Demonstrating the procedure will be Sydney Brigido, a research assistant from my laboratory. Sydney will assist with the various steps of the protocol.

To prepare a participant for transcranial direct current stimulation, after placing the head strap on the participant, stand behind the participant to establish the location for the cathodal electrode using the previously calculated 10%of head circumference and measure this distance out from the inion of the head to the right. Place the cathodal electrode according to the measurements such that it is approximately behind the right ear on the mastoid process. To establish the location for the anodal electrode, measure out the previously calculated 10%of head circumference from the nasion up and the previously calculated 5%of head circumference to the right.

Place the anodal electrode and verify that the anode is touching the 10 to 20 EEG electrode AF3FP1 locations. When the electrodes have been placed, turn on the tDCS device and plug in the electrodes. To load setting A, press the top right button to exit out of study mode and use the top and bottom left buttons to enter the master code of the device.

Click OK and make sure the arrow is pointing at trigger. Use the top right button to move through the settings until load setting appears. Use the left arrows to scroll the arrow to the bottom of the screen using the top right arrow to move through all the settings back to setting A and click the top left arrow to load setting A.Press the top right and bottom left buttons together to check the impedance to confirm that there is adequate contact between the tDCS electrodes and the participant's skull.

Start the stimulation and record the impedance prior, during, and after the stimulation. At the completion of the stimulation, remove the electrodes from the device before turning off the device. Place two self-adhesive disposable electrodermal activity electrode patches on the thenar region of the participant's non-dominant hand and open the electrodermal activity galvanic skin response data acquisition software.

Open the previously generated data acquisition template and click create record to create a new experiment. To calibrate the electrodermal activity signal, attach an electrode to an electrode patch and follow the software instructions to calibrate one electrode at a time. When both the electrodes have been calibrated, ask the participant to take a deep breath in and to hold it for 10 seconds before breathing out to ensure an adequate galvanic skin response signal.

To administer the tDCS, have an assistant turn on the virtual reality system and open the patient application program. Check that the screen resolution is set to 1280 by 720 and click play. Open the clinician controller program and select the driving scenario based on the scene that is most relevant to the participant's deployment.

Under the patient avatar window, select the driver position and set the sound volume to 65%of maximum. With the assistance of the participant, have the assistant place the head-mounted display on the participant's head, taking care that the display does not dislocate the electrodes and check for comfort. Have the assistant place the headphones on the participant's head and check for comfort.

Instruct the participant to sit quietly for two minutes to allow the baseline electrodermal activity data to be collected and press F1 to mark the beginning of the baseline period. After two minutes, press F3 to mark the end of the baseline period. After completion of the baseline electrodermal activity collection, turn on the tDCS device and plug the electrodes back in.

The device should be in study mode for setting B.Click OK to confirm that setting B is programmed and to apply a two milliamp intensity, total of 25 minutes with a 30-second ramp up and 30-second ramp down. Enter the participant-specific randomization code retrieved from the randomization software and click OK.Press the top left button to indicate yes to start the stimulation and click off to start the drive. Ensure that each drive-through starts with at least 30 seconds of driving only in the VR environment.

For the first session, guide the participant through the occurrence of VR events using a verbal prompt during the first drive-through such as, Up ahead, there will be a road ambush in three, two, one, go. You're going to see a road ambush up ahead in three, two, one. While selecting the appropriate scene in the VR menu.

Administer each VR event with a minimum of 10 seconds of driving between each event. While the VR events are being administered, have an assistant press F2 on the keyboard every time a VR event is administered to monitor the skin conductance data acquisition. Based on visual inspection of the skin conductance traces, participant A appears to show signs of between-session habituation from the first VR session to the midpoint of the protocol during the third VR session to the final sixth VR session.

Visual inspection of the raw skin conductance tracing for participant B appears to indicate within-session habituation when comparing the first drive-through to the third drive-through. Visual inspection of raw skin conductance data for participant C appears to show a less stark habituation profile compared to participant A.Nonetheless, participant C demonstrates both between and within-session habituation. Furthermore, and similar to participant A, the skin conductance level is numerically higher during the first VR session compared to the remaining five sessions.

Raw skin conductance data from participant D demonstrates a skin conductance level that can be considered too low for proper analysis with an absence of visually detectable skin conductance responses. Even with the persistence of artifacts and electrode signal loss, the persistently low skin conductance levels and absence of visually detectable skin conductance responses are still apparent for this individual. In the protocol, critical steps are to ensure the tDCS electrodes remain in the correct position, that impedance is within acceptable values, and to watch for participant discomfort for safety.

tDCS can be optimized by individualizing the montage, including the location of electrodes and dosing based on anatomical MRI. MRI can further be used to assess neural changes over time.