Transcranial Magnetic Stimulation (TMS) is a non-invasive therapy specifically targets brain regions that are implicated in different mental illnesses. The TMS coils that we use at Clear Path Psychiatry are configured to provide broad-based, deep stimulation. We use Brainsway H coils, including the H1 coil and the H7 coil. The H1 coil targets both dorsolateral prefrontal cortices (DLPFCs), with a preference for the left DLPFC; the H1 coil is FDA-cleared for the treatment of major depressive disorder and has an expanded FDA indication for treatment of “anxious depression.” The H7 coil targets the medial prefrontal cortex (MPFC) and anterior cingulate cortex (ACC), midline structures in the front of the brain. The H7 coil is FDA-cleared for treatment of obsessive-compulsive disorder and major depressive disorder.
These brain regions are interconnected and can be thought of as a circuit—we can selectively target distinct parts of the circuit to alleviate symptoms of depression or OCD.
A course of conventional TMS with the H1 coil typically consists of one 20-minute treatment per day, 5 days per week, for four weeks (20 sessions), followed by two treatments per week for an additional twelve weeks, for a total of 44 treatments. With once-daily TMS, most people notice benefit by the 3rd or 4th week, and improvement gradually continues through the twice-weekly phase. The conventional, once-daily TMS protocol using the H7 coil for treatment of OCD is 29 treatments: once-daily 18-minute treatments, five days per week, for 5 weeks, followed by 4 treatments in the final week.
The first day of treatment, your provider will perform a mapping procedure and assess your “motor threshold.” During the mapping, the coil will be moved around to determine the optimal spot that causes a part of your body to twitch. For the H1 coil, we move the coil to find the best spot to induce a twitch in your right hand or thumb. For the H7 coil, we move the coil around to find the best location to cause a twitch in your feet (either foot). After finding the best location, the intensity of the impulse is adjusted until it causes the body part to twitch 50% of the time. This intensity is known as your motor threshold and differs between individuals. TMS is administered at an intensity related to your individual motor threshold. After the mapping procedure is complete and motor threshold assessed, the coil is moved to the treatment location. Most TMS protocols for depression stimulate the left dorsolateral prefrontal cortex (LDLPFC), a region that has been shown to be underactive in depression. An alternative TMS protocol for depression inhibits an overactive right dorsolateral prefrontal cortex (RDLPFC). The H7 coil stimulates the medial prefrontal cortex and anterior cingulate cortex to alleviate symptoms of depression and/or obsessive-compulsive disorder (OCD). Your provider will assess your symptoms and determine which coil, target, and protocol are best suited to treat your depression or OCD.
The DLPFC is connected to several brain circuits implicated in depression: the salience network, which helps to focus attention on some things and ignore others; the default mode network, which is active when a person is not engaged in any particular task and is active when the mind wanders; and the executive network, which is involved in planning, decision-making and impulse control. Scientists think that abnormal communication between neural networks, or circuits, can lead to constant rumination, self-criticism, and tendency to focus on negative aspects of life that people with depression often experience. TMS can help reset faulty circuits. The LDLPFC is also extensively interconnected with various subcortical regions (deep brain regions), including the “limbic system,” which is comprised of the amygdala, hippocampus, and striatum. The limbic system is the emotional center of the brain. The LDLPFC-limbic circuit is heavily involved in emotion processing and regulation. TMS protocols that stimulate an underactive LDLPFC have consistently demonstrated antidepressant efficacy. Another less commonly utilized TMS protocol targets the right dorsolateral prefrontal cortex, or RDLPFC, which has been shown to be overactive in depression. The parameters of a TMS coil can be adjusted such that they suppress an overactive RDLPFC.
Studies have shown that TMS can stimulate neurons to sprout new dendrites, the branched appendages that receive signals from other neurons. Using magnetic fields to stimulate the brain, TMS induces a remarkable phenomenon known as neuroplasticity. This process involves the brain’s innate ability to rewire and adapt to changes in the environment.
In the context of mental illness, TMS targets regions associated with mood regulation, cognition, and emotional processing. Through carefully calibrated magnetic pulses, TMS encourages neurons to forge new connections and enhance communication between brain regions.
Appendix
ACC = anterior cingulate cortex
DLPFC = dorsolateral prefrontal cortex
MPFC = medial prefrontal cortex