What is non-invasive neuromodulation?
Non-invasive neuromodulation techniques, by definition, are options to act on brain structures, modifying, activating or inhibiting their functionality, through non-aggressive devices, with few contraindications and minimal side effects. There are two basic non-invasive brain stimulation treatment techniques: repetitive Transcranial Magnetic Stimulation (rTMS) and Direct Current Electrical Stimulation (tDCS). Recently, other options have emerged, today with fewer consolidated therapeutic indications.
Transcranial Magnetic Stimulation (rTMS)
Transcranial Magnetic Stimulation (TMS) is a form of non-invasive stimulation of the human cerebral cortex. It consists in the production of a very brief electric current which, when passing through a small copper wire coil placed on the scalp, generates a magnetic field of sufficient intensity to penetrate the skull and depolarize the neurons of the cortex located 1.5 – 2 cm below. TMS can be administered in single pulses or, since a few years ago, in the form of trains (series of regular repetitive pulses), of variable frequency and duration. In the latter case it is called Repetitive Transcranial Stimulation (rTMS), this variant being much more capable of stimulating the cerebral cortex in a lasting manner.
Transcranial Direct Current Stimulation (tDCS)
Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that consists of applying a constant low-intensity electrical current to the scalp (between 0.5 -2 mA), between two electrodes, to modulate cortical excitability. Generally speaking, anodal tDCS improves cortical excitability while cathodal tDCS inhibits the stimulated areas, although some factors may have an influence depending on the distance and orientation of the axons and dendrites with respect to the electric field.
Although the mechanisms of action underlying tDCS-induced modulation of neuronal activity are not yet fully understood, it has been shown that the current interferes with the resting membrane potential of neuronal cells, which modulates the spontaneous activity of brain circuits (could have an effect on the strength of neuronal synapses), altering the activity of NMDA and GABA receptors, thus triggering the process of plasticity, such as long-term potentiation (LTP) and long-term inhibition (LTD).
The advantages of using tDCS include its low cost, ease of application, and safety. To date, there is no evidence of serious adverse events after applying tDCS in healthy individuals, as well as in patients with neurological conditions, such as stroke.
This technique has been successfully used for the treatment of some of the most common symptoms suffered by people who have suffered brain damage, whether in the motor, cognitive or emotional sphere. And it has a wide acceptance in the treatment of depression and pain.
In what pathologies is it applied?
Repetitive transcranial magnetic stimulation (rTMS) is a therapeutic reality in post-stroke rehabilitation, since it confers neuroprotective effects, favorably affecting the modulation of neuroplasticity (NP), thus helping the brain in its capacity to readapt neuronal circuits and, with this, the restoration and acquisition of new compensatory skills. Different studies have shown improvement in motor disorders, aphasia, dysarthria, oropharyngeal dysphagia, depression and perceptual-cognitive difficulties that appear in these patients.
It is also applied in neurological disorders such as Parkinson’s syndrome, dystonia, tics, tinnitus, spasticity, pain, either neuropathic or migraines, dementia…
Among the psychiatric disorders of therapeutic application are depression, anxiety, OCD, schizophrenia and post-traumatic stress syndrome.
Numerous specialists in Clinical Neurophysiology offer this therapeutic alternative in several disorders and it has already been approved in some countries in the treatment of depressions refractory to medication. It is reasonable to expect an increasing introduction of this technique in the coming years.
Side effects of Transcranial Magnetic Stimulation (TMS)
The safety of the technique is supported by numerous experts, who state that patients with implanted aneurysm clips or other metallic devices, a pacemaker or hearing aids should not undergo TMS. Or if you are at risk of being pregnant or at risk of becoming pregnant during the sessions, as well as suffering from serious heart or circulatory diseases.
However, the risk of epileptic seizures in healthy subjects is very low. Transient hearing problems are easily solved by placing earplugs in the ears during the technique.
The most frequent side effects are vasovagal syncope due to the tension associated with the procedure. Some patients may also experience isolated discomfort in the form of a post-procedure headache without consequences. Discomfort during the test has been described if there are contractions of the facial musculature or neck pain due to the position maintained during the test if the duration is prolonged.
Isolated cases of mania, psychotic breaks, anxiety, agitation, suicidal ideation and insomnia have been reported.