TMS and the Dorsolateral Prefrontal Cortex

Transcranial magnetic stimulation (TMS) is a non-invasive method of brain stimulation used for therapeutic purposes and to study brain function. The dorsolateral prefrontal cortex, or DLPFC, is a region in the brain’s frontal lobes that is a frequent target for this technique. The application of TMS to the DLPFC has become a significant area of research and clinical practice, particularly for treating conditions that involve mood and cognitive regulation.

Understanding the Dorsolateral Prefrontal Cortex

The dorsolateral prefrontal cortex is located on the upper and outer surface of the brain’s frontal lobes. Its placement makes it accessible to non-invasive stimulation techniques.

This brain region is central to cognitive processes known as executive functions. These processes include working memory, which allows for holding and manipulating information, and cognitive flexibility, the ability to switch between tasks. The DLPFC also contributes to planning complex actions and exercising inhibitory control, the capacity to suppress automatic responses.

Beyond cognition, the DLPFC has a recognized role in mood regulation. It is a component of larger brain circuits connecting emotional processing with higher-order thought. Dysregulation within these circuits is thought to contribute to symptoms seen in various psychiatric conditions.

Principles of Transcranial Magnetic Stimulation

Transcranial magnetic stimulation operates on the principle of electromagnetic induction. A device containing a magnetic coil is placed against the scalp, where it generates brief magnetic pulses. These pulses pass through the scalp and skull without requiring incisions.

Once the magnetic field reaches the brain, it induces small electrical currents in the neural tissue. Depending on the stimulation’s parameters, such as frequency and intensity, the activity of the targeted brain cells can be either increased or decreased.

For therapeutic purposes, a technique called repetitive TMS (rTMS) is used. Unlike single-pulse TMS, which is often used for research, rTMS delivers a series of pulses over a session to produce longer-lasting changes in brain activity.

Therapeutic Applications for DLPFC-TMS

In conditions like depression, certain brain networks connected to the DLPFC are observed to be underactive. The goal of TMS is to modulate the activity in these circuits, aiming to restore a more typical level of function.

The most established therapeutic application for TMS targeting the DLPFC is for Major Depressive Disorder (MDD). Treatment protocols for depression often involve high-frequency stimulation of the left DLPFC to increase its excitability. This approach is based on findings that show reduced activity in this area in individuals with depression.

While MDD is the primary condition for which DLPFC-TMS is approved, it is also an approved treatment for Obsessive-Compulsive Disorder (OCD). Further investigations are exploring its potential benefits for anxiety disorders, post-traumatic stress disorder (PTSD), and smoking cessation.

The treatment’s effectiveness can lead to significant improvements in depressive symptoms. The induced changes in the DLPFC are thought to propagate through connected brain regions, including deeper areas involved in emotion like the anterior cingulate cortex.

What to Expect During Treatment

The treatment process begins with a mapping session where a clinician identifies the precise location on the patient’s head corresponding to the DLPFC. They also determine the correct stimulation intensity by finding the motor threshold, the minimum power required to cause a small twitch in the hand muscles.

During a treatment session, the patient is awake and seated comfortably in a chair. When the device is active, it produces clicking sounds and the patient will feel a tapping sensation on their scalp. Each session lasts between 20 and 40 minutes.

A standard course of treatment involves daily sessions, five days a week, for four to six weeks. After the initial course is complete, some individuals may benefit from periodic maintenance sessions to sustain the therapeutic effects.

Common side effects are mild and temporary. They can include:

• Headaches
• Lightheadedness
• Discomfort at the stimulation site
• Twitching in facial muscles during the pulse delivery

A rare but more serious risk is the potential to induce a seizure, though treatment protocols are designed to minimize this risk.