Combining TMS & fMRI » fmri.at | neuroimaging & stimulation

Approaches

Magnetic Resonance Imaging and Transcranial Magnetic Stimulation (TMS) have both immense potential in the field of neuroscience:

Structural and functional MRI allow for mapping cognitive functions to spatial and temporal features of brain activation.
TMS holds the potential to infer on causal relationships between brain areas and cognitive functions.
TMS and fMRI can support each other based on their respective advantages when combined.

MRI can used to improve brain stimulation before, after and during TMS. TMS applied during fMRI allows for the investigation of immediate neural effects — Combining TMS with fMRI. Offline approaches utilise fMRI before TMS to determine stimulation targets and after TMS to investigate lasting changes after rTMS. Finally, in online TMS/fMRI, TMS is applied during fMRI allowing for the investigation of immediate neural effects due to stimulation.

fMRI before, after and during TMS

Magnetic resonance imaging complements TMS in different ways

Anatomical images acquired before TMS can be fed into the neuronavigation software to define the actual stimulation site.
fMRI acquired before TMS allows for functional definition of a stimulation target.
Offline imaging (e.g. fMRI during task or in resting-state) allows for evaluating long-term effects after TMS.
Finally, fMRI during TMS, i.e. concurrent TMS/fMRI, allows for the direct observation of TMS-induced effects.

Concurrent TMS/fMRI

Methods for concurrent use of imaging and TMS were developed to examine TMS evoked responses in detail. This combination allows for the investigation of direct and localized neural effects as well as network effects due to TMS stimulation, yielding studies that go beyond simple observation of behavioural changes. There are, however, a number of challenges that have to be addressed for successful imaging of TMS online effects.

**Advanced TMS/fMRI setup** for whole-brain imaging. In addition to the TMS/fMRI coil array, a second coil on the contralateral side enables whole-brain coverage. This setup further includes an MR-adapted neuronavigation system to guarantee online tracking for evaluation of stimulation efficacy.

Concurrent TMS/fMRI coil array

The ideal concurrent imaging & stimulation setup has a high-density of multi-channel receive coils that are positioned directly on the subject’s scalp to maximise signal to noise ratio.