Transcranial magnetic stimulation: types and uses in therapy

There are a large number of disorders and diseases that affect the brain and its function. These disorders can cause or be caused by why different areas of the brain are sometimes not activated enough or function in an altered way. To solve them, different mechanisms and treatments have been elaborated or tried to elaborate with greater or lesser efficacy. One of them, not very well known but which has shown some usefulness, is transcranial magnetic stimulation.

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What is transcranial magnetic stimulation?

The technique known as transcranial magnetic stimulation is a method or type of non-invasive intervention that is based on the application of magnetic fields controlled to stimulate nerve cell activity. This stimulation does not generate pain and allows a control of the activity of the target brain areas.

The principle by which it works is the application of electromagnetic induction, applying electric current to an electromagnet that is placed on the scalp in such a way that the aforementioned magnetic fields are generated (sufficiently attenuated so as not to generate damage).

Thus, these fields influence the transmission of information, facilitating brain activity (although it is not fully understood how it works) and the generation of action potentials through neuronal depolarization. The normal rhythm of activation of these neurons is interrupted, something that can in turn generate delayed effects in those neurons with which those affected by stimulation connect. It has been linked to depression and long-term potentiation.

The studies carried out so far seem to indicate that it is a methodology that has some effectiveness and that it has few risks, although it is usually used as an alternative method or as a support to the treatment carried out and not as a first option (other types of treatment that have shown greater consistency and effectiveness are usually preferred).

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Basic procedure

The basic procedure that is usually followed in the application of transcranial magnetic stimulation is approximately the following. Prior to treatment, a visit to the doctor should be made to check that the patient does not present any type of pathology or element for which this technique is contraindicated.

Regarding the application itself, first of all, after entering the room, the patient will be provided with some kind of barrier element such as earplugs so that they can protect their ears. Previously should or would be recommended explain to the patient what will happen during the session, and it may be necessary to reassure the patient (without using anesthesia or sedatives).

Next, a coil with an electromagnet is placed on the scalp, placing it in the area to be stimulated. It is possible that instead of one, there are two or more elements to be placed, depending on how the stimulation is carried out. The brain mapping or mapping will be carried out, introducing brief pulses to observe and locate the brain areas and their bioelectric functioning. You are likely to notice some sensations and sounds in this phase.

After that, the doctor will proceed to turn on the coil and adjust the intensity of the stimulation, increasing it to the motor threshold (generally to generate the contraction of the fingers). After reaching it, finally, the magnetic field will be allowed to pass for a variable period of time depending on each case. These sessions can vary in number and timing, with around ten sessions being customary.

Types of transcranial magnetic stimulation

There are different ways to apply transcranial magnetic stimulation. Some of the main types are as follows.

1. Single pulse transcranial magnetic stimulation

One of the ways to apply this technique is with simple pulses, through the application of a stimulus every three or more seconds, or with a train of stimuli of varying frequency over the same area for several seconds. Used in research or in the treatment of a specific problem.

2. Transcranial magnetic stimulation of paired pulses

In this case, two stimuli are applied whose intensity can be the same or different from each other, through the same coil and in the same brain region or with two different coils. Typical of the study of corticocortical connectivity.

3. Repetitive transcranial magnetic stimulation

This application is one of the best known. It is based on the emission of repeated pulses, applying a stimulus (of low frequency) or more (being able to reach twenty in the fast or high frequency rTMS) per second or less time. It is usually used in the treatment of neuropsychiatric problems.

In what diseases is it used?

Although not particularly recognized, transcranial magnetic stimulation has been applied to different brain and psychiatric disorders. Some of the best known are the following.

1. Parkinson's and motor syndromes

One of the disorders in which the use of this technique is most frequent is in Parkinson's or in problems related to its symptoms, causing functional improvements and reduction of motor problems.

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2. Mood disorders

Perhaps the best known psychiatric application of this technique is in major depression. With a running partly similar to electroconvulsive therapy but without its side effects, it has been observed that this treatment contributes to reduce depressive symptoms if applied in the left dorsolateral prefrontal bone, although it requires further investigation

It has also been applied in the treatment of Bipolar disorder, although in this case there is a risk of inducing manic episodes. That is why in this disorder it is necessary to take special precaution.

3. Neurorehabilitation

Another application area is in neurorehabilitation, using stimulation as a way to generate neuronal activation and to try to improve functionality after a brain injury. It is applied among others in trauma, heart attacks, spinal cord injuries, neglect syndromes, hemiparesis or cognitive difficulties.

4. Epilepsy

Epilepsy is a disorder in which this type of treatment has sometimes been used. It can allow the stimulation of some relevant brain areas in order to alleviate deterioration generated by this condition, and can even facilitate the appearance of epileptic seizures in order to locate the area that generates the seizures and assess the possibility of other therapeutic options.

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5. Pain disorders

The use of transcranial magnetic stimulation has been considered in the treatment of problems that occur with pain, such as neuropathies and neuralgias, or phantom hand pain (in amputees), fibromyalgia, or even migraine.

6. Neurodevelopmental disorders

There is research that suggests the use of this therapy in autism and ADHD, using stimulation on the nuclei that govern attention to provoke improvements in the symptoms of these neurodevelopmental disorders and stimulating their attentional capacity. However, much more research is still needed in this regard.

7. Schizophrenia and psychotic problems

Depending on the use and the areas stimulated, it is possible to find a utility of this technique in the case of schizophrenia and psychotic disorders. This is especially useful in stimulating the mesocortical pathways, so that negative symptoms are reduced. Also in some cases it can be used in the treatment of positive symptoms by altering the brain mechanism that produces them (although there is a risk of generating psychotic outbreaks).

Contraindications and side effects

As we have said, transcranial magnetic stimulation is generally considered an option. non-invasive and low-risk therapy, with no major complications in most cases. cases. However, this does not mean that it cannot have annoying side effects or even be contraindicated in specific cases.

When it comes to side effects, generally patients who undergo this treatment may experience headaches and dizziness, ants, and paresthesias on the face and scalp or even some small involuntary spasms. Occasionally, however, more serious disturbances such as hearing loss, seizures, and manic episodes can occur. That is why, although apparently low risk, caution must be exercised with its use.

With regard to people who have transcranial magnetic stimulation contraindicated or who are required, consult or inform their doctor of the presence of characteristics Before undergoing it, those who have implants or have some metallic element lodged in their body that could be altered by stimulation stand out. magnetic. Especially relevant is the case of pacemakers (which the stimulation could alter to the point of causing death), infusion pumps, elements and valves implanted in the nervous system or cochlear implants. Something as simple as dental implants can also pose a certain danger, as well as shrapnel or metal elements present in the body due to some type of accident or trauma.

People suffering from brain injuries such as strokes also require special caution. recent (although it is sometimes used as a rehabilitation of its effects, it is not advisable to apply it in infarcted). Although it is used as therapy in some cases of bipolarity or schizophrenia, special caution should be taken in these cases since if the subject's condition is not controlled the appearance of psychotic outbreaks or manic episodes can be favored. The same goes for epilepsy. Those who consume any type of medication (whether or not psychotropic) should consult their doctor first. Finally, pregnant women are also contraindicated this treatment.

Bibliographic references

• Ibiricu, M.A. & Morales, G. (2009). Transcranial magnetic stimulation. Anales del Sistema Sanitario de Navarra, 32 (Suppl. 3). Pamplona.
• López-Ibor, J.J.; Pastrana, J.I.; Cisneros, S. & López-Ibor, M.I. (2010). Efficacy of transcranial magnetic stimulation in depression. Naturalistic study. Acts Esp. Psychiatry, 38 (2): 87-93.
• Pascual-Leone, A. and Tormos-Muñoz, J.M. (2008). Transcranial magnetic stimulation: fundamentals and potential of modulation of specific neural networks. Rev. Neurol., 46 (Suppl 1): S3-S10.