THETA BURST STIMULATION

Overview of Repetitive Transcranial Magnetic Stimulation.

TMS stands for transcranial magnetic stimulation. Transcranial means “through the skull,” and magnetic stimulation means that the magnetic field will penetrate through the skull and cause activation of the brain cells underneath without causing any harm while doing so. Whoever came up with the name transcranial magnetic stimulation was trying to explain how it works. Unfortunately, it made it a little bit confusing for the general public to understand transcranial magnetic stimulation. For this reason, I prefer terminology like magnetic brain therapy. The classical form of transcranial magnetic stimulation applies a magnetic field similar in power and intensity to the magnetic field used in an MRI machine to the area of the brain called the DLPFC or the dorsolateral prefrontal cortex.

Read more on How TMS therapy works.

The magnetic pulses are delivered at a frequency of 10 Hz, meaning that 10 pulses per second. Each train of pulses is delivered for 4 seconds. This means each train of pulses is 40 pulses. A break between the trains of pulses is between 11 to 26 seconds. Then a new train of pulses comes along for another 10Hz X 4 Seconds = 40 pulses. This is repeated for 75 trains. By doing the simple math, we can find out that we deliver 10 (Hz) X 4 (Sec) X 75 (Trains) = 3000 pulses. So technically, the patient is receiving 3000 pulses of stimulation each session. This particular stimulation of the brain cells will activate this area of the brain in the frontal lobe, which is connected to the limbic system.

Learn about the pros and cons of TMS

The limbic system is where we feel emotions, pain, depression, sadness, enjoyment .. etcetera. Waking up the cells that connect to the limbic system could improve depressive symptoms in over half of the patients who are going through TMS. Just like when somebody goes to the gym to build muscle mass, they're not going to lift weight only once and expect to be bodybuilders for the sudden.

Learn more about TMS patient experiences.

They probably would need to do it in sets, and they would need to do it daily for a while before they start building muscle tissue or muscle mass. A similar idea applies to brain stimulation with TMS. You can just use the simulating magnetic pulses for one day and expect that the brain will maintain this stimulation. You will need to do it daily, five days a week, for six weeks, for a total of 30 treatment sessions. The chances of someone with treatment-resistant depression responding to this protocol is about 58%, which is significantly better than medications at this stage of the depression course. 

The question then is how to make TMS even better. The pursuant of a better TMS led us to theta-burst stimulation.

What is theta wave?

Theta wave frequency refers to the frequency of brain waves in the range of 4 to 7 Hz.  Some brain circuits use this particular frequency as an oscillation wave. Theta frequency is the language that the brain circuits used to speak to each other. Mainly it is the oscillation frequency used by the hippocampus to connect to other brain circuits.  Theta frequency is observed when the brain forms memories, deep meditation, or specific sleep phases.  In other words, it seems like when the brain wants to create long-lasting skills; it uses theta frequency. For this reason, it was suggested that by using the same frequency in stimulation, the brain could be more effective and more efficient. 

Learn about TMS for anxiety

What is theta-burst stimulation?

Theta-burst stimulation is a form of transcranial magnetic stimulation that uses theta frequency to stimulate the brain. Using the same frequency that the brain uses to communicate with its internal circuits, we might be more effective and time-efficient.

With theta-burst stimulation, we deliver a triplet of pulses at a frequency of 50 hertz for 200 milliseconds intervals for a train duration of 2 seconds which means a total of 10 triples of pulses in 2 seconds. This is a total of 30 pulses. Because those 10 bursts of pulses are delivered in 2 seconds trains, this gives it a frequency of 5 Hz, which is in the range of what we called above theta wave frequency, the frequency used by the hippocampus to communicate with other circuits of the brain. Because this is more effective in stimulating the brain, we don't need to do it for 75 trains, and we could just get away with 20 trains. Also, the interval between the trains is only 8 seconds, saving even more time. Doing the math here, it means that you were giving 3 (triplet pulse) X 5 (Hz) X 2 (Sec) X 20 (trains) = 600 pulses. 

Success rate of TMS therapy? Click here to learn more.

Similar to rTMS. We need to do iTBS daily, 5 days a week, for 6 weeks, for a total of 30 treatment sessions.

How effective is theta-burst stimulation?

Some researchers believe that theta-burst stimulation is even more effective than 10 Hz repetitive transcranial magnetic stimulation. We know for sure that, at least, iTBS (Intermittent theta burst stimulation) is as effective as rTMS (repetitive transcranial magnetic stimulation). This was proven in a large non-inferiority trial called the TREE-D trial, which resulted in the FDA approval for theta-burst stimulation in 2018. 

The importance of theta-burst stimulation.

Theta burst stimulation opens the door wide open to other modalities of treatment like accelerated TMS. In an accelerated TMS, we can use theta-burst stimulation in multiple sessions a day to achieve the same results that we were achieving over six weeks in just about one week. Theta-burst stimulation can also decrease the cost of TMS. This is because it takes less time to treat patients, which means that one device can treat more patients a day, making the treatment more cost-effective. 

There had been particular interest in theta-burst stimulation for indications other than depression. For example, treatment of bipolar disorder, negative symptoms of schizophrenia,  central pain syndrome, and fibromyalgia.

rTMS vs iTBS

This compassion table breaks down head-to-head repetitive transcranial magnetic stimulation vs. intermittent theta-burst stimulation.