Transcranial magnetic stimulation during fMRI; investigating neuronal activation during TMS

Transcranial magnetic stimulation (TMS) is a method that can temporarily alter
brain activity in a safe and non-invasive way. It is currently used in many
different clinical and research settings. However, as of yet there is
restricted knowledge about the TMS induced field patterns and accurate TMS
dosage. Previous research has attempted to predict neuronal activation during
TMS by making electromagnetic models and validating these by mapping TMS
magnetic fields with an MR scanner. However, most studies attempting to map the
magnetic field of TMS coils have used simplifications of current TMS
techniques, making it difficult to generalize these results to a more realistic
TMS setup. Recently, our group has developed a new TMS-MRI setup that makes it
possible to accurately map TMS magnetic fields using a realistic TMS setup as
often used both in clinical and research settings. Using this setup, we can
validate electromagnetic models of TMS coils and correct guidance and dosimetry
for concurrant TMS-MRI, so that more crude methods such as the motor threshold
to determine individual TMS dosage is no longer needed.

The objective of the current study is to validate computational models that
predict neuronal activation during TMS.

We aim to observe the effect of TMS on the healthy brain by having 10 healthy
adults undergo one session of concurrent TMS stimulation and an MRI scan, and
one session of MRI without concurrent TMS. During the session with concurrent
TMS and MRI we will also use the scanner*s default ECG apparatus, normally used
for heart rate measurement during MR scans, to measure TMS-induced thumb
movement of the hand. This measurement will be repeated outside the scanner
with a dedicated EMG device at a later visit.
In the MRI, we will stimulate two of the most important locations in the brain
for TMS research; M1 in the motor cortex and the left dorsolateral prefrontal
cortex (DLPFC), and the temporo-parietal junction (TPJ).
This is an observational study in which healthy participants will undergo
concurrent TMS stimulation ,fMRI measurements, DTI measurements and MR phase
mapping methods in order to evaluate the TMS field.
The total duration of study participation will be approximately five hours.

The risk associated with participating in an fMRI-TMS experiment is minimal. It
is not considered greater than when fMRI or TMS is applied in isolation. The
potential risks of bringing a TMS coil into the bore of an MRI scanner have
been eliminated by the special setup that is designed by our research group. A
comparable setup was used in a previous study by our group, which has been used
in x participants without any adverse events. The setup currently developed
even has an extra safety built in, controlling not only the opening but also
the closing of the relay. For known potential hazards of fMRI and TMS, the
usual precautions are taken such as careful screening of participants.