TMS

Transcranial Magnetic Stimulation (TMS) is a non-invasive procedure that uses magnetic fields to modulate cells in the brain. Our system is the DuoMAG XT-100 (see here), and the manual can be found here. We have the capability to run Repetitive, Burst and Single-Pulse research protocols. This can be used in conjunction with our Neuro-Navigation system (BrainSight) using participant MRI or template space, alongside sequential recording of other modalities (MRI or EEG).

Brain stimulation techniques such as TMS can be guided by neuro-navigation techniques that use the participants native space (i.e. anatomical MRI) or template space (e.g. MNI152) to target a region of interest.

../_images/Stim1.jpg

Prescreening

The TMS Safety Questionnaire must be filled in by research participants before they can undergo stimulation. Once your participant has filled it in, it is your responsibility to go through the questions carefully with them to check that they are safe to participate. Verify with a supervisor before accepting participant.

TMS Safety Questionnaire

Important

Please take notice of these requirements when recruiting participants: Neurological Conditions; Previous Head Traumas; Piercings and Tattoos; Medication; Any metals inside the body;

Motor Thresholds

Most protocols will require a Motor Threshold (Active or Resting) calculation for each participant to ensure appropriate stimulation output. This must be done prior to the stimulation. Please see this video on how to implement this within the GUI.

Setting Up EMG

The system comes with a built-in Electromyography (EMG) module to record Motor-evoked potentials during threshold calculation/single pulse protocols.

  1. Ensure batteries for EMG headbox are charged (If empty, TMS protocols will not run)

  2. Prep skin on (dominant) hand with alcohol wipe

  3. Place the Ground strap onto the wrist/arm

  4. Black electrode should be placed on the belly of dorsal interosseous muscle (Contract thumb into hand to tense)

  5. Red electrode should be placed below middle joint of the index finger

  6. Plug in connectors to the EMG headbox (colour coded)

  7. Check signal quality on GUI readout on MEP/MT MODE

Calculating Thresholds

Ensure you have selected which threshold type and the target value you desire (settings) before calculation.

Approximating the hand-knob within motor cortex:

  1. Measure nasion to inion, take 50% value, mark it

  2. Measure 2cm out from mark (contralateral to dominant hand), mark it

For Resting MT:

  1. Ensure participant is as relaxed as possible (with potential limb support)

  2. Enable TMS coil (start at 40% stimulator output)

  3. Deliver single-pulse TMS over motor cortex

  4. Dial up/down intensity of stimulation until MEPs are evident (between 50-100 microvolts) at least 50% of the time

For Active MT:

  1. Ask participant to make a voluntary contraction at maximum output pressing their thumb and index finger together

  2. Select ‘Ch1’ to log maximum

  3. Ask participant to go back to resting (values should be as close as possible to target)

  4. Enable TMS coil (start at 40% stimulator output)

  5. Deliver single-pulse TMS over motor cortex

  6. Dial up/down intensity of stimulation until MEPs are evident (between 50-100 microvolts) at least 50% of the time

Important

Please ensure that participants are static (except relevant hand) during this procedure by using either a head or chin rest.