Our protocol, investigators can design and validate novel virtual reality tools to assist in the diagnosis and characterization of unilateral spatial neglect. This technique provides a broad array of data sets for the study of unilateral spatial neglect. It also avoids possible confounding effects seen in studies of patients with acquired brain injury.
Better characterization of unilateral spatial neglect can facilitate the delivery of therapy to patients with subtle but still debilitating deficits and potentially improve their overall recovery. Demonstrating the procedure will be Sam Cason and Peter Schwab, researchers from my laboratory. To perform the Line Bisection test have the subject sit at a table directly across from the tester and provide the subject with a writing utensil and the stimulus sheet ensuring that the sheet is placed directly in front of the subject.
Instruct the subject to quickly and accurately bisect each line printed on the stimulus sheet as close to the middle of each line as possible while keeping their head and shoulders centered as much as possible. To perform the Bells Test provide the subject with the Bells Test stimuli sheet and instruct the subject to circle or cross out all of the bells on the sheet as quickly and accurately as possible while keeping their head and shoulders as centered. To perform the star cancellation test present the subject with the stimulus sheet ensuring that it is placed directly in front of them and instruct the subject to circle or cross out all of the stars on the stimulus sheet as quickly and accurately as possible with their head and shoulders centered.
To perform the Otas circle cancellation test provide the subject with the Otas circle cancellation stimulus sheet and instruct the subject to cross out or circle all of the open incomplete circles as quickly and as accurately as possible with their head and shoulders as centered. Before the first TMS session upload the subject's 3TT1 MRI scan into the neuro navigational software and create a 3D representation of the subject's brain. During the first session, have the subject sit in front of an optical tracking camera and use a headband or glasses to place a tracker on the subject.
Attach one disposable disc electrode on the subject's right dorsal interosseous, one disc electrode to the subject's second knuckle on the right pointer finger and one ground electrode to the subject's right wrist, right hand, and wrist. Plug the electrodes into an electrode adapter that inputs into an MEP tracking software program and select, new online session to open the subject's project within the neuro navigational software. Select the targets to be stimulated in this session and using a pointer registered to the neuro navigational software touch the subject's face in the same locations that the landmarks were placed.
Open the validation tab in the software and use the pointer to touch the subject in various spots on the head, ensuring that the cross hairs on the screen line up with the spot being pointed to on the subject. Plug a handheld TMS coil into the TMS machine and turn on the TMS machine. Set the instrument to single pulse and set an appropriate stimulation intensity.
Placing the handheld TMS coil on the left side of the subject's head, deliver stimuli to the motor cortex using TMS single pulses. To identify the location that stimulates the first dorsal interosseous. Alter the stimulation intensity until the stimulation elicits MEP's of at least 50 millivolts exactly five out of 10 times.
This intensity is considered the resting motor threshold. Replace the handheld coil with an air cooled TMS coil with a built-in cooling system targeting the SMG or STG for active sessions or the vertex for sham sessions and set the stimulation parameters to repetitive TMS at a rate of one Hertz for 20 minutes at a 110%intensity of the resting motor threshold. Then start stimulation of the target of interest.
To perform the virtual reality behavior test place the VR headset onto the seated subject's head with the straps secured tightly but comfortably. Give the subject both controllers and ensure that both eyes are visible by visually confirming they are centered in the pupil core software camera feeds. In the unity editor, open the virtual reality task and press the play button.
Ask the subject to look straight ahead and click the tear camera button. Click the begin tutorial button and wait for the subject to complete the tutorial. When subject is finished, click the calibrate eye tracking button and click next trial to begin the first trial.
When the subject has completed the trial click the play button again to end the task. In this analysis the average head angle was examined to determine whether the virtual reality task was sensitive enough to identify a difference between the SMG and STG groups. ANCOVA analysis of head angle differences between groups revealed a significant difference in head angle change scores between the pre and post TMS groups.
This finding from the virtual reality task is consistent with the results of the traditional paper and pencil task as both demonstrated a pattern in which the SMG group may have had a subtle neglect and looked more toward the right compared to the STG group. To specifically assess for signs of allocentric neglect on an individual target level flowers can be separated by which side of the flower contains the defective petals. In this analysis, participants in the SMG group had a tendency to look further to the right at a higher flower to head angle when searching for the short petal on the right side of the flower compared to the angle observed when the short petals were on the left side of the flower.
When the average number of seconds that participants looked at each flower were analyzed no significant difference in mean head angle change score was observed between the SMG and STG groups. This method is limited by the subtle clinical effects achieved with repetitive transcranial magnetic stimulation. So proper stimulation parameters in cortical region targeting are critical.
