Transcranial Magnetic Stimulation (TMS)

Transcranial magnetic stimulation, also called TMS, is a non-invasive method of brain stimulation that, through a coil - device capable of storing electrical energy generated in a magnetic field. This coil, among biological tissues that have magnetic permeability, penetrates the scalp and skull without causing the magnetic field to suffer a significant decrease, sending electromagnetic stimuli to the brain that generate a reaction in the individual’s body. This reaction that the pulses promote can be used to treat diseases such as depression, Parkinson’s disease and tinnitus, as well as for motor rehabilitation and studies on brain functioning.

Repetitive pulses can be inserted into the brain in an excitatory way, in order to promote an action, or inhibitory, causing an action to stop happening.

TMS, when applied to the motor cortex, passes to pyramidal neurons, which pass to the subcortical region, which cause reactions in the corticospinal tract, reaching motor neurons and, finally, the target muscle.

Depending on the type of coil, its positioning on the scalp and the field strength, restricted areas of the sensorimotor cortex can be stimulated. The point on the scalp where magnetic stimulation constitutes a response of maximum amplitude and most easily in a given target muscle is considered the preferential location, or “hot spot”, for recording the pulse electromagnetic to this muscle.

TMS Neuronavigation

Neuronavigation is a real-time visualization technique, so you can see where to position instruments in relation to neuronal structures, using computerized or magnetic resonance images as a reference. The position of the instruments is monitored in real time using a graphical computer interface. Thus, it is possible to check the positioning of a stimulation coil during TMS.

When guided by neuronavigation, TMS is called nTMS: Navigated Transcranial Magnetic Stimulation, and allows you to consider anatomical differences - eventual differences found in the human form that do not cause any harm to the function of that part - between individuals. It has been shown that using neuronavigation, motor thresholds achieved are more stable, allowing for more accurate and reproducible stimulation.

Variations in coil orientation and rotation may occur throughout a TMS session, which may result instimulation of other than the area of ​​interest. This adversity is overcome by neuronavigation, which allows defining and monitoring the ideal location and orientation of stimulation.

Motor Mapping

It’s a technique of delimiting the area of ​​representation of the target muscle on its cortical surface. This technique is used in studies of brain physiology to assess damage to the motor cortex and corticospinal tract and to evaluate the functional representation of muscle in the brain.

The Motor mapping is used in brain surgeries, enabling greater precision when carrying out the procedure and certainty of the location in which it will be performed. Another advantage is that it reduces the risk of postoperative complications, such as motor deficits.

Repetitive Transcranial Magnetic Stimulation

A rTMS, Repetitive Transcranial Magnetic Stimulation, is abundantly used in the therapeutic area, according to the frequency of the pulse sequence. Applications of rTMS to the cortex can act in an excitatory manner, reactivating regions of little activity, or in an inhibitory manner, reducing very active regions. This therapy process is done in sessions, in the beginning with many of them and over time they decrease, according to the patient’s progress.

Motor Evoked Potential

The most commonly extracted information from the MEP is amplitude and latency. The amplitude peak-to-peak is used to represent signal intensity, being defined as the difference between the maximum and minimum MEP values. Latency is the time interval between the application of the TMS pulse and the start of the MEP. These two characteristics are important because they contain information about cortical structures, the integrity of the corticospinal tract and the muscle fibers recruited.