TMS – Transcranial Magnetic Stimulation
Transcranial magnetic stimulation (TMS) is a magnetic method used to stimulate specific regions of the brain. During a TMS procedure, a magnetic field generator, or “coil,” is placed near the head of the person receiving the treatment. Through electromagnetic induction, the coil delivers small electric currents into the focused brain area. The coil is connected to a pulse generator, or stimulator, that delivers electric current to the coil.
Single TMS is used diagnostically to measure the connection between the brain and a muscle to evaluate damage from stroke, multiple sclerosis, amyotrophic lateral sclerosis, movement disorders, motor neuron disease and injuries.
rTMS – Repetitive Transcranial Magnetic Stimulation
Using rTMS evidence suggests the efficacy of the technique for neuropathic pain (brain area focus: motor) and treatment-resistant major depressive disorder (left Cortex PreFrontoDorsoLateral).
The greatest risks of TMS are the rare occurrence of syncope (fainting) and even less commonly, induced seizures. Other adverse effects of TMS include discomfort or pain, transient induction of hypomania, transient cognitive changes, transient hearing loss, transient impairment of working memory, and induced currents in electrical circuits in implanted devices.
The effect of rTMS on the cortex depends on stimulation frequency. When the motor cortex is the target, frequencies above 1 Hz lead to local excitation, whereas frequencies below 1 Hz trigger inhibition. Stimulation depth seems to depend on the shape of the coil. A figure-of-eight coil only allows for very superficial stimulation (2 cm), whereas a double-cone coil results in deeper stimulation.
In recent years, the PFC has been the main target in trials of rTMS in OCD, based on the hypothesis of right PFC hypermetabolism in anxiety disorders and depression. In accordance with this hypothesis, several studies have been carried out either with low-frequency stimulation of the right PFC or high-frequency stimulation of the left PFC, with conflicting findings.