TMS is a neuromodulatory technique which applies magnetic pulses to the brain via a ‘coil.’ An electric current is delivered to the coil, which acts as the magnetic field generator in the procedure. The generated magnetic field induces an electrical current in the brain. Different coil types are used to elicit different magnetic field patterns, and using more focal points can elicit a deeper magnetic field to stimulate deeper cortical layers. Stimulation is typically applied at a sufficient intensity to trigger action potentials in proximate neurons. For example, TMS over the motor cortex can result in a finger twitch. Applying several pulses of TMS in a row is called repetitive TMS or “rTMS.” The timing of the pulses can determine how the brain changes in response. rTMS can sometimes disrupt how a brain region is working, leading to what is called a “functional lesion.” This selective interference gives it credence in therapies aiming to modulate the relative excitability of a brain region. Additionally, when combined with other neuroimaging techniques, TMS can be used to map behavior related circuitry with spatial and temporal precision.1 rTMS can lead to lasting changes in brain function which is why it is used for treatment. Long-term potentiation (LTP) and long-term depression (LTD) are the implicated cellular mechanisms behind rTMS. Some areas TMS is currently being explored include: stroke rehabilitation, parkinson’s, depression, migraine, pain management, and auditory hallucination.
What is the TMS device look like?
A TMS stimulator is the size of mini-fridge and has a power cable. It will have various controls on it to adjust stimulation parameters such as pulse intensity, number of pulses, and pulse frequency. The coil looks like one or more loops. For example, a “figure-8 coil” is two touching loops. A cable connects the coil to the stimulator. The coil is held over the head (the part to be stimulated) by the hand of the operator, or by a mechanical arm.
What does TMS feel like? What are the side-effects?
Common side-effects effects of TMS stimulation are related to discomfort on the scalp. This discomfort should go away after the TMS session. Rarely, someone might faint or have a seizure while undergoing stimulation. Other potential side effects include: a transient confusion related to disruptions in cognition, hearing, or vision.
Where can I get TMS?
In the United State rTMS has been approved by the FDA for the treatment of some kinds of depression.
1Siebner, H. R., Bergmann, T. O., Bestmann, S., Massimini, M., Johansen-Berg, H., Mochizuki, H., … & Pascual-Leone, A. (2009). Consensus paper: combining transcranial stimulation with neuroimaging. Brain stimulation, 2(2), 58-80.