Assessing Corticospinal Pathways Using Transcranial Magnetic Stimulation

Begin with a seated participant, with electrodes positioned on the leg muscles, the tibialis anterior, and the soleus muscles.

Fix a tracker to monitor the head position.

Place the transcranial magnetic stimulation or TMS coil over the brain’s motor cortex region that controls leg muscles.

Apply a magnetic stimulus to one hemisphere of the brain.

The signal travels from the brain through the corticospinal tract within the spinal cord to the contralateral leg, producing a muscle response.

Determine the lowest TMS intensity that evokes a consistent muscle response.

Then, apply a higher TMS intensity while the participant remains relaxed, and record the baseline corticomotor response or CMR.

Next, repeat the TMS delivery at the same intensity while the participant pulls their foot upward, and record the CMR.

Compared to rest, an increased CMR during activity allows assessment of the corticospinal pathways controlling the leg muscles.

Begin tonic voluntary activation testing by first determining the maximum voluntary isometric contraction of each muscle bilaterally. For each motion, instruct the subject to maximally contract the contralateral examined muscle four times. Next, verify the positio