When transcranial magnetic stimulation (TMS) technology was first developed in 1985, its effectiveness and reach into the brain was limited. While it first began to explore the possibility of using magnetism in psychiatric medicine, as a pain-free and non-invasive way to physically affect the brain, much progress has been made since in terms of speed, consistency, and reliability.
Among the improvements made over the decades, one of the advancements with the greatest impact include the introduction of deep transcranial magnetic stimulation (dTMS), which more than doubles the effective reach of transcranial magnetic waves, to the theoretical limit of what would still be effective in terms of depth and distance.
But to understand how dTMS improves upon older forms of TMS technology, including the dominant repetitive transcranial magnetic stimulation (rTMS), it’s critical to understand what TMS is and how it uses our modern understanding of inductance and induction, and electromagnetics to affect the human brain in a safe way.
What is TMS Technology?
First developed over three decades ago, TMS technology makes use of magnetic waves to affect the state of neurons in the brain, effectively triggering the cells to fire in a certain way. The magnetic waves affect the electric impulses through which cells communicate – this principle of bioelectricity traces back to the days of experimenting with dead frog legs and electrical currents.
Today, we know that everything from the muscles in our body to the thoughts we have are transmitted through chemical reactions and electrical impulses, and that magnets affect how electricity moves by pulling and pushing electrons. Harmless, completely non-invasive magnetic waves – the same kind produced by an MRI machine – are used to go beyond the skin and skull to affect the action potential of our neurons, essentially changing how and when they fire.
This helps doctors effectively try and mechanically change some of the portions of the brain associated with symptoms of mental illness – chiefly major depressive disorder (MDD) and obsessive-compulsive disorder (OCD).
Because these waves must be of a specific and constant intensity in order to be strong enough to affect the brain, there’s always been a severe limitation on how far they could penetrate through the scalp before running into technical issues. This has changed with dTMS technology.
The Difference Between rTMS and dTMS
Repetitive transcranial magnetic stimulation and deep transcranial magnetic stimulation are set apart from one another due to the type of coils used when setting up the treatment process.
TMS technology involves the use of a specialized machine attached to headgear, which is built to house a coil that sends generated magnetic waves through the coil, past the hair and scalp, into the brain. Repetitive transcranial magnetic stimulation uses a figure-eight coil. The maximum penetration into the brain with rTMS technology lies at about 1.5cm (half an inch). Each treatment session takes about 40 minutes.
Deep transcranial magnetic stimulation utilizes a completely different coil design, which allows for magnetic waves to reach further into the brain, for about 4 cm (over one and a half inches).
This enables not only increased efficacy of the treatment (meaning it’s more effective for more people), but it also allows for shorter treatment sessions (about 20 minutes, half the time of an rTMS treatment session) and enables a TMS specialist to target other previously inaccessible portions of the brain, thus unlocking the ability to target other disorders such as OCD.
When is TMS Used for Depression Treatment?
While TMS technology is proven effective for depression treatment, much of the research surrounding it is specifically aimed at its ability to treat people who are treatment-resistant – in other words, patients who have tried multiple different forms of talk therapy and antidepressant medication, and still struggle with severe depressive symptoms.
TMS therapy can be pricey, but it is largely covered by insurance if you have proven that first line depression treatment is ineffective in your case.
Once you have been approved for TMS treatment, the exact nature of the treatment will depend on a doctor’s decision. TMS technology is usually used to target the dorsolateral prefrontal cortex on one side of the brain, so a technician and medical professional will be present during each session to properly administer the treatment.
Because it is painless and non-invasive, there is no need for sedation, anesthesia, or prior medication. Speak to your psychiatrist and doctor about your medical history before getting TMS treatment, to avoid potential complications.
Why So Many Sessions?
TMS treatment usually requires about 20 to 30 sessions, at a rate of about five sessions per week, for four to six weeks. Each session varies in length, but typically, they last less than half an hour.
The reason so many sessions are needed is because the effects of TMS require adaptation – the brain has to take into account the changes that have occurred and adjust accordingly. Different people require different amounts of treatment, and the rate at which treatment begins to affect a person’s mental state is also varied. Some people respond faster than others, and some don’t respond until the treatment has concluded.
The more sessions you take, the more your brain begins to get used to the changes made during each session. It is, in effect, like training a muscle – by progressively training the muscle and placing it under a certain amount of stress, you prompt your body to redirect resources to building it up, making it more resilient and more able to handle similar stresses in the future.
The analogy isn’t perfect, but it is meant to illustrate the point that, just like muscle building, TMS takes time. Sadly, it isn’t always effective. While more than half of patients who have attempted TMS treatment have had positive results on a significant level, there are also many who did not see lasting or meaningful changes or didn’t see any changes at all.
TMS addresses a number of different potential factors for depression, but it is not a perfect solution to this often incredibly complex disorder, and it helps to try and receive antidepressant treatment concurrently while undergoing TMS therapy.
As research continues into unraveling the neurological aspects of depressive disorders and other forms of mental illness, treatments like TMS will continue to be vital in affecting the right changes in the brain, without risk of adverse effects as in other forms of neuromodulation.