Transcranial magnetic stimulation by a permanent magnet (TMSPM)

What is TMS

Following article writes about conventional TMS therapy.

Transcranial Magnetic Stimulation (TMS): A Non-Invasive Approach to Brain Modulation

Transcranial Magnetic Stimulation (TMS) is a cutting-edge, non-invasive neurostimulation technique that has emerged as a significant therapeutic option for various neurological and psychiatric conditions. By utilizing magnetic fields to induce electrical currents in targeted brain regions, TMS offers a unique way to modulate neural activity and alleviate symptoms, particularly for individuals who have not responded to conventional treatments.

What is TMS and How Does It Work?

At its core, TMS operates on the principle of electromagnetic induction. A device called a stimulator generates rapidly changing electric pulses, which are delivered to a magnetic coil placed against the patient’s scalp. This varying electric current creates a pulsed magnetic field that can penetrate the skull and induce a secondary electric current in the underlying brain tissue. This induced electrical current then either excites (depolarizes) or inhibits (hyperpolarizes) nerve cells (neurons) in the targeted brain area, thereby modulating their activity.

The depth of penetration typically ranges from 2 to 4 cm, depending on the coil and intensity used. However, advanced forms like “Deep TMS” (dTMS) can reach up to 6 cm into the brain, stimulating deeper regions.

The effects of TMS can be categorized based on the frequency, duration, and intensity of the stimulation:

  • Single or paired-pulse TMS: These deliver a single pulse or two consecutive pulses, primarily used for diagnostic purposes (e.g., mapping motor cortex activity) or to study cortical excitability.
  • Repetitive TMS (rTMS): This involves delivering repeated magnetic pulses in trains over several minutes, leading to longer-lasting effects on brain activity. Low-frequency rTMS (less than 1 Hz) is generally thought to inhibit cortical firing, while high-frequency rTMS (greater than 1 Hz) is believed to provoke it.

The exact mechanism by which rTMS produces its therapeutic effects is still being actively researched, but it is thought to involve changes in synaptic efficacy, similar to long-term potentiation (LTP) and long-term depression (LTD), which are fundamental processes of learning and memory in the brain. It is also believed to influence the release and balance of neurotransmitters like serotonin and dopamine, which play crucial roles in mood regulation.

Indications for TMS

TMS has gained significant recognition for its efficacy in treating various conditions, particularly those resistant to other forms of therapy. The U.S. Food and Drug Administration (FDA) has approved TMS for:

  • Major Depressive Disorder (MDD): Especially for treatment-resistant depression where patients haven’t found adequate relief from antidepressant medications. TMS typically targets the left dorsolateral prefrontal cortex (DLPFC), an area often underactive in depressed individuals.
  • Obsessive-Compulsive Disorder (OCD): TMS is used to modulate specific brain regions implicated in OCD symptomatology.
  • Smoking Cessation: For individuals struggling to quit smoking.
  • Migraines: As a preventative or acute treatment for certain types of migraines.

Beyond these FDA-approved indications, research continues to explore the potential of TMS for a range of other conditions, including:

  • Post-Traumatic Stress Disorder (PTSD)
  • Tourette Syndrome
  • Chronic Pain Syndrome
  • Generalized Anxiety Disorder (GAD)
  • Bipolar Disorder (though careful monitoring for hypomanic symptoms is necessary)
  • Movement Disorders: Such as Parkinson’s disease, functional tremors, focal epilepsy, cortical myoclonus, and spasticity.
  • Schizophrenia: Particularly for managing negative symptoms and auditory hallucinations.
  • Autism
  • ADHD
  • Speech disorder
  • Stroke
  • Senile dementia

Duration, Frequency, and Dosages

TMS treatment protocols vary depending on the condition being treated and individual patient response.

  • Duration of a single session: A typical TMS session can last anywhere from 20 to 60 minutes. Some newer protocols, like Theta Burst Stimulation (TBS), deliver the same number of pulses in a much shorter timeframe, sometimes as little as 6-10 minutes.
  • Frequency of sessions: For conditions like depression, TMS is commonly administered five days a week (Monday through Friday) for several weeks.
  • Overall course of treatment: A standard course of TMS for depression usually involves 4 to 6 weeks of daily sessions, totaling 20 to 30 sessions. Some individuals may require additional “booster” or maintenance sessions to sustain long-term benefits.
  • Dosage/Intensity: The intensity of the magnetic pulses is crucial for effectiveness. It is typically determined by first identifying the motor threshold (MT), which is the lowest pulse intensity that causes a visible twitch in a specific hand muscle (e.g., thumb) when the motor cortex is stimulated. Therapeutic TMS is then delivered at a percentage of this MT, often around 110-120% of the resting motor threshold for conditions like depression. The total number of pulses delivered over the course of treatment is considered a measure of the overall “dose.” For example, a common protocol might deliver 3,000 pulses per 30-minute session, amounting to 90,000 pulses over a six-week course.

Individualized dosing is crucial, and some research is exploring electric field (E-field) based dosing to reduce variability in stimulation strength across individuals and brain regions.

Side Effects

One of the significant advantages of TMS over other brain stimulation therapies or medications is its generally favorable side effect profile. Most side effects are mild and transient.

Common Side Effects (usually mild and temporary):

  • Headache: This is the most common side effect, often experienced during the first few sessions and typically resolving within a few hours. Over-the-counter pain relievers can help manage it.
  • Scalp discomfort or pain: A sensation of warmth or discomfort at the coil placement site is common. Adjustments to coil placement or intensity can often alleviate this.
  • Lightheadedness: Some individuals may feel lightheaded during or immediately after a session.
  • Muscle twitching: Temporary twitching in facial muscles or the jaw can occur due to the electrical pulses.
  • Fatigue or drowsiness: Approximately one in three individuals may experience tiredness after a session, especially during the initial week.
  • Temporary hearing issues: The TMS machine produces a loud clicking sound. Proper ear protection (earplugs) is essential during every session to prevent this. Some patients may also experience temporary increased sensitivity to sound or, rarely, tinnitus.

It’s important to note that TMS does not cause brain tumors or memory loss. These are common misconceptions often confused with electroconvulsive therapy (ECT), which has a different mechanism and side effect profile.

Conclusion

Transcranial Magnetic Stimulation offers a promising and often effective non-invasive treatment option for individuals struggling with various brain-related conditions, especially those resistant to conventional therapies. Its ability to precisely target and modulate brain activity, coupled with a relatively mild side effect profile, makes it a valuable tool in modern psychiatry and neurology. As research continues to unravel the intricacies of brain function and the mechanisms of TMS, its applications and efficacy are likely to expand, offering hope to many.