Technical Details of Online Circuit Engagement Using TMS inside MRI Scanner

A variety of approaches to interleave functional MRI with TMS have been accomplished and yield complementary evidence for circuit engagement and modulation. The include gaps between TRs to prevent corruption of images, throwing out corrupted fMRI volumes if acquired concurrently with TMS, and even inter-slice TMS delivery. Triggering the scanner and the TMS box can be managed with a single host computer running a variety of software (psychopy, eprime, matlab, etc.). Controlling for non-specific effects of stimulation is typically carried out by comparing other active stimulation sites given that there is no commercially available sham TMS compatible with the MRI environment. Using fMRI to guide TMS positioning extends beyond the TMS/fMRI environment but is an important consideration in deciding how to do a valid TMS/fMRI experiment. Considerations including the strength of the evidence for the target, the amount and type of imaging data, weighting individualized targets based on atlases or coordinates from the imaging literature, as well as practical considerations such as the likelihood of causing scalp pain at a particular location and the distance of the brain from the scalp. The audience will be shown several fMRI ‘blobs’ from a real participant and will be polled on which target they would choose. This will be compared with the target we actually selected from the experiment along with a rationale for the choice.