TMS: How Does It Work?

How does it treat depression? What are the risks and benefits?

6 min

TMS is a form of neuromodulation used for treatment-resistant depression. Here is how electricity and magnets come together to make us feel better.

TMS: How Does It Work?

How does it treat depression? What are the risks and benefits?

6 min
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While medications work by adjusting the levels of neurotransmitters, hormones or other substances in the body, brain stimulation methods generally work by directly stimulating or inhibiting areas of brain tissue with electricity. While there is much variation between the different types of brain stimulation, they each offer their own set of pros and cons and should be considered as options for management of MDD. The most commonly used tools in the field of brain stimulation are electo-convulsive therapy (ECT or “shock” therapy) and transcranial magnetic stimulation (TMS). Generally, treatment for newly-diagnosed MDD will initially begin with therapy and/or anti-depressant medications. ECT or TMS are treatments that are typically reserved for those whose depression is resistant to medications, those who have difficulty taking medications, or those who have unique symptoms.

Transcranial Magnetic Stimulation (TMS) is a technology used for treating MDD which has not improved with medications. If you have tried multiple antidepressant medications without significant improvement, your physician may consider TMS as a medication-free approach for your depression.

How it works: TMS works by Faraday’s principle: a rapidly changing magnetic field can create an electrical current in a nearby conductor (like a wire). The neurons in the brain work like insulated wires, and therefore researchers have found that by shifting strong magnets next to the brain, they can create electrical currents in the brain’s neurons, leading to the release of neurotransmitters. Therefore, instead of increasing the amount of neurotransmitters at the synapse by taking medications, a TMS machine stimulates your own neurons to release more of their own neurotransmitters. 

To understand this, imagine the fetal brain as a mound of sand. As the human brain develops, new neural circuits are formed, like the paths carved into the sand as water poured onto the sand flows in various directions. In depression, these circuits can become overly restricted, with too much water going down a deeper valley in the sand and other areas remaining completely dry. TMS allows providers to stimulate the areas of the brain that, like dry land between valleys, become underactive in MDD. Namely, studies have found decreased activity in the dorsolateral prefrontal cortex (frontal cortex near the temples) of those with MDD. Like a flat, dry sand dune between several streams, there is no current here, so the land has dried up. While ECT would wash over the entire environment like a tsunami, repetitiveTMS (or rTMS) is like a hose spraying a new path through a specific, important area of the dry dunes. It is a targeted way of creating a new stream little-by-little. By repeatedly spraying a specific area of the sand dune, we eventually create a few new streams that can begin to catch rainfall and develop into bigger, wider valleys in the future. The mechanism of TMS is therefore to repeatedly stimulate (and release neurotransmitters from) brain circuits between specific areas of the brain that become underactive in MDD.

What to expect: In a TMS treatment, our provider will have us seated comfortably in a chair. They’ll then place something like a swim cap on our head and will take measurements of our head to find certain areas targeted for treatment. Typically, they will use a spot on the left side near our head’s temple. They will then try different electromagnetic strengths until our thumb twitches. This strength is unique to each individual and will help to determine which settings we’ll need for treatment. Once this is determined, the machine will begin its treatment, which will last between a few minutes and a half-hour, depending on which treatment protocol is used.

After treatment: After treatment, we may feel a bit energized or clear-minded. We may have some scalp discomfort under the area that was stimulated, which some describe as a headache.

Since there is no need to swallow and digest any medications, there are none of the bodily side effects that antidepressant medications tend to cause (upset stomach, sexual dysfunction, insomnia, etc.). TMS does not require us to undergo anesthesia (unlike ECT, which requires anesthesia), so it is less risky than ECT. Additionally, there is no memory loss associated with TMS, unlike ECT where memory loss is common.

TMS evidence: In a large study, one-in-two patients who received TMS had improvement in their depression symptoms with one-in-three patients achieving remission (no further symptoms) from their MDD.

Don’t get TMS if: You have any metal in the head, neck, or chest. This may include clips, cochlear implants, stents, nerve stimulators, defibrillators, etc.

TMS summary: TMS is a generally safe and comfortable treatment for those who have MDD that has not been responding to antidepressants. The side effects of TMS are less than those associated with antidepressants and ECT.

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