This month, we will explore another method for treating neurological disorders through neurotechnology: transcranial magnetic stimulation (TMS). In contrast to deep brain stimulation, which we explored last month, TMS does not require a surgically-placed electrode. Rather, it consists of a set of electrical wires contained in an insulated coil held at the surface of the skull, that deliver short pulses with a strong magnetic field. This magnetic field leads to a charge, which produces a subsequent current in the neural tissue below the area of the skull where the device was placed, although some devices are able to induce pulses that spread further. The procedure is usually administered daily for 20-45 minutes for a period of 4-6 weeks. In order to determine where exactly to place the device, professionals make use of fMRI images and frameless stereotaxic software.
The stimulation frequency lies between 1-30 Hz and the device acts as a neuromodulator that can either excite or inhibit brain activity. This neuromodulating ability allows for this technique to have multiple uses: it can be used as treatment for a variety of neurological disorders, such as schizophrenia, depression, or obsessive compulsive disorder; for research, to explore the types of connections that occur in the human brain; or for diagnosis of spinal cord and motor neuron diseases such as multiple sclerosis or stroke. One of the main focuses of study has been the effects of TMS on major depressive disorder. Antidepressant medication has many negative side effects, one of them being sleep deprivation. It has been found that patients that suffer from depression that take antidepressant medication can be treated with TMS to reduce the side effects of the medication and increase their quality of life. Beyond this, researchers are investigating the effects of TMS on sleep itself. For instance, in a study conducted in 2013, 120 patients that suffered from chronic primary insomnia were treated with TMS and the researchers concluded that TMS improved the quality of sleep, especially in stage III of the sleep cycle and REM sleep. Some potential uses for TMS that require further experimentation are TMS as an alternative treatment for Parkinson’s disease or the potential for neural enhancement. Previous experiments with TMS have shown patients that experienced greater finger-reaction time or higher memory, abstract thinking, motor learning, and color perception skills.
The long-term impact of TMS is another factor under investigation. The efficiency and long-term effects of TMS rely on the specific part of the brain that requires the stimulation and the duration and intensity of the stimulation. To this day, all the positive and negative effects of TMS have been very short-lived. And, even though it is less invasive than DBS because it does not require the insertion of an electrode in the brain, there have been very few controlled studies carried out that show that TMS is indeed an effective treatment for all the disorders outlined above. In addition, the exposure to such strong magnetic fields, especially if the treatment is administered multiple times for long periods of time, could potentially be damaging for the brain itself. Treatments that require internal or external brain stimulation require more studies and trials before their effectiveness can be concluded, however, scientists are getting closer to increasing their efficacy and decreasing their side effects with success.